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ARM (stylised in lowercase as arm, formerly an acronym for Advanced RISC Machines and originally Acorn RISC Machine) is a family of
reduced instruction set computer In computer engineering, a reduced instruction set computer (RISC) is a computer designed to simplify the individual instructions given to the computer to accomplish tasks. Compared to the instructions given to a complex instruction set comp ...
(RISC)
instruction set architecture In computer science, an instruction set architecture (ISA), also called computer architecture, is an abstract model of a computer. A device that executes instructions described by that ISA, such as a central processing unit (CPU), is called an ...
s for computer processors, configured for various environments.
Arm Ltd. Arm is a British semiconductor and software design company based in Cambridge, England. Its primary business is in the design of ARM processors (CPUs). It also designs other chips, provides software development tools under the DS-5, RealView ...
develops the architectures and licenses them to other companies, who design their own products that implement one or more of those architectures, including
system on a chip A system on a chip or system-on-chip (SoC ; pl. ''SoCs'' ) is an integrated circuit that integrates most or all components of a computer or other electronic system. These components almost always include a central processing unit (CPU), memor ...
(SoC) and
system on module A system on a module (SoM) is a board-level circuit that integrates a system function in a single module. It may integrate digital and analog functions on a single board. A typical application is in the area of embedded systems. Unlike a si ...
(SOM) designs, that incorporate different components such as memory, interfaces, and radios. It also designs cores that implement these
instruction set architecture In computer science, an instruction set architecture (ISA), also called computer architecture, is an abstract model of a computer. A device that executes instructions described by that ISA, such as a central processing unit (CPU), is called an ...
s and licenses these designs to many companies that incorporate those core designs into their own products. There have been several generations of the ARM design. The original ARM1 used a
32-bit In computer architecture, 32-bit computing refers to computer systems with a processor, memory, and other major system components that operate on data in 32- bit units. Compared to smaller bit widths, 32-bit computers can perform large calculati ...
internal structure but had a 26-bit
address space In computing, an address space defines a range of discrete addresses, each of which may correspond to a network host, peripheral device, disk sector, a memory cell or other logical or physical entity. For software programs to save and retrieve s ...
that limited it to 64 MB of
main memory Computer data storage is a technology consisting of computer components and recording media that are used to retain digital data. It is a core function and fundamental component of computers. The central processing unit (CPU) of a comput ...
. This limitation was removed in the ARMv3 series, which has a 32-bit address space, and several additional generations up to ARMv7 remained 32-bit. Released in 2011, the ARMv8-A architecture added support for a
64-bit In computer architecture, 64-bit integers, memory addresses, or other data units are those that are 64 bits wide. Also, 64-bit CPUs and ALUs are those that are based on processor registers, address buses, or data buses of that size. A ...
address space and 64-bit arithmetic with its new 32-bit fixed-length instruction set. Arm Ltd. has also released a series of additional instruction sets for different rules; the "Thumb" extension adds both 32- and 16-bit instructions for improved
code density In computer science, an instruction set architecture (ISA), also called computer architecture, is an abstract model of a computer. A device that executes instructions described by that ISA, such as a central processing unit (CPU), is called an ...
, while
Jazelle Jazelle DBX (direct bytecode execution) is an extension that allows some ARM processors to execute Java bytecode in hardware as a third execution state alongside the existing ARM and Thumb modes. Jazelle functionality was specified in the ARMv5TEJ ...
added instructions for directly handling
Java bytecode In computing, Java bytecode is the bytecode-structured instruction set of the Java virtual machine (JVM), a virtual machine that enables a computer to run programs written in the Java programming language and several other programming langua ...
. More recent changes include the addition of
simultaneous multithreading Simultaneous multithreading (SMT) is a technique for improving the overall efficiency of superscalar CPUs with hardware multithreading. SMT permits multiple independent threads of execution to better use the resources provided by modern proces ...
(SMT) for improved performance or
fault tolerance Fault tolerance is the property that enables a system to continue operating properly in the event of the failure of one or more faults within some of its components. If its operating quality decreases at all, the decrease is proportional to the ...
. Due to their low costs, minimal power consumption, and lower heat generation than their competitors, ARM processors are desirable for light, portable, battery-powered devices, including
smartphone A smartphone is a portable computer device that combines mobile telephone and computing functions into one unit. They are distinguished from feature phones by their stronger hardware capabilities and extensive mobile operating systems, whi ...
s,
laptop A laptop, laptop computer, or notebook computer is a small, portable personal computer (PC) with a screen and alphanumeric keyboard. Laptops typically have a clam shell form factor with the screen mounted on the inside of the upper li ...
s and
tablet computer A tablet computer, commonly shortened to tablet, is a mobile device, typically with a mobile operating system and touchscreen display processing circuitry, and a rechargeable battery in a single, thin and flat package. Tablets, being com ...
s, and other
embedded system An embedded system is a computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is ''embedded ...
s."Some facts about the Acorn RISC Machine"
Roger Wilson posting to comp.arch, 2 November 1988. Retrieved 25 May 2007.
However, ARM processors are also used for desktops and
server Server may refer to: Computing *Server (computing), a computer program or a device that provides functionality for other programs or devices, called clients Role * Waiting staff, those who work at a restaurant or a bar attending customers and su ...
s, including the world's fastest
supercomputer A supercomputer is a computer with a high level of performance as compared to a general-purpose computer. The performance of a supercomputer is commonly measured in floating-point operations per second ( FLOPS) instead of million instructio ...
( Fugaku) from 2020 to 2022. With over 230 billion ARM chips produced, , ARM is the most widely used family of
instruction set architecture In computer science, an instruction set architecture (ISA), also called computer architecture, is an abstract model of a computer. A device that executes instructions described by that ISA, such as a central processing unit (CPU), is called an ...
s (ISA) and the ISAs produced in the largest quantity. Currently, the widely used Cortex cores, older "classic" cores, and specialised SecurCore cores variants are available for each of these to include or exclude optional capabilities.


History


BBC Micro

Acorn Computers Acorn Computers Ltd. was a British computer company established in Cambridge, England, in 1978. The company produced a number of computers which were especially popular in the UK, including the Acorn Electron and the Acorn Archimedes. Acorn's ...
' first widely successful design was the BBC Micro, introduced in December 1981. This was a relatively conventional machine based on the
MOS Technology 6502 The MOS Technology 6502 (typically pronounced "sixty-five-oh-two" or "six-five-oh-two") William Mensch and the moderator both pronounce the 6502 microprocessor as ''"sixty-five-oh-two"''. is an 8-bit microprocessor that was designed by a small te ...
CPU but ran at roughly double the performance of competing designs like the
Apple II The Apple II (stylized as ) is an 8-bit home computer and one of the world's first highly successful mass-produced microcomputer products. It was designed primarily by Steve Wozniak; Jerry Manock developed the design of Apple II's foam-m ...
due to its use of faster
dynamic random-access memory Dynamic random-access memory (dynamic RAM or DRAM) is a type of random-access semiconductor memory that stores each bit of data in a memory cell, usually consisting of a tiny capacitor and a transistor, both typically based on metal-ox ...
(DRAM). Typical DRAM of the era ran at about 2 MHz; Acorn arranged a deal with
Hitachi () is a Japanese multinational conglomerate corporation headquartered in Chiyoda, Tokyo, Japan. It is the parent company of the Hitachi Group (''Hitachi Gurūpu'') and had formed part of the Nissan ''zaibatsu'' and later DKB Group and Fuyo G ...
for a supply of faster 4 MHz parts. Machines of the era generally shared memory between the processor and the
framebuffer A framebuffer (frame buffer, or sometimes framestore) is a portion of random-access memory (RAM) containing a bitmap that drives a video display. It is a memory buffer containing data representing all the pixels in a complete video frame. Mode ...
, which allowed the processor to quickly update the contents of the screen without having to perform separate
input/output In computing, input/output (I/O, or informally io or IO) is the communication between an information processing system, such as a computer, and the outside world, possibly a human or another information processing system. Inputs are the signals ...
(I/O). As the timing of the video display is exacting, the video hardware had to have priority access to that memory. Due to a quirk of the 6502's design, the CPU left the memory untouched for half of the time. Thus by running the CPU at 1 MHz, the video system could read data during those down times, taking up the total 2 MHz bandwidth of the RAM. In the BBC Micro, the use of 4 MHz RAM allowed the same technique to be used, but running at twice the speed. This allowed it to outperform any similar machine on the market.


Acorn Business Computer

1981 was also the year that the
IBM Personal Computer The IBM Personal Computer (model 5150, commonly known as the IBM PC) is the first microcomputer released in the IBM PC model line and the basis for the IBM PC compatible de facto standard. Released on August 12, 1981, it was created by a tea ...
was introduced. Using the recently introduced
Intel 8088 The Intel 8088 ("''eighty-eighty-eight''", also called iAPX 88) microprocessor is a variant of the Intel 8086. Introduced on June 1, 1979, the 8088 has an eight-bit external data bus instead of the 16-bit bus of the 8086. The 16-bit registers and ...
, a
16-bit 16-bit microcomputers are microcomputers that use 16-bit microprocessors. A 16-bit register can store 216 different values. The range of integer values that can be stored in 16 bits depends on the integer representation used. With the two ...
CPU compared to the 6502's
8-bit In computer architecture, 8-bit integers or other data units are those that are 8 bits wide (1 octet). Also, 8-bit central processing unit (CPU) and arithmetic logic unit (ALU) architectures are those that are based on registers or data buses ...
design, it offered higher overall performance. Its introduction changed the desktop computer market radically: what had been largely a hobby and gaming market emerging over the prior five years began to change to a must-have business tool where the earlier 8-bit designs simply could not compete. Even newer
32-bit In computer architecture, 32-bit computing refers to computer systems with a processor, memory, and other major system components that operate on data in 32- bit units. Compared to smaller bit widths, 32-bit computers can perform large calculati ...
designs were also coming to market, such as the
Motorola 68000 The Motorola 68000 (sometimes shortened to Motorola 68k or m68k and usually pronounced "sixty-eight-thousand") is a 16/32-bit complex instruction set computer (CISC) microprocessor, introduced in 1979 by Motorola Semiconductor Products Secto ...
and
National Semiconductor NS32016 The NS32000, sometimes known as the 32k, is a series of microprocessors produced by National Semiconductor. The first member of the family came to market in 1982, briefly known as the 16032 before becoming the 32016. It was the first 32-bit gener ...
. Acorn began considering how to compete in this market and produced a new paper design named the
Acorn Business Computer The Acorn Business Computer (ABC) was a series of microcomputers announced at the end of 1983 by the British company Acorn Computers. The series of eight computers was aimed at the business, research and further education markets. Demonstrated at t ...
. They set themselves the goal of producing a machine with ten times the performance of the BBC Micro, but at the same price. This would outperform and underprice the PC. At the same time, the recent introduction of the
Apple Lisa Lisa is a desktop computer developed by Apple, released on January 19, 1983. It is one of the first personal computers to present a graphical user interface (GUI) in a machine aimed at individual business users. Its development began in 1978. ...
brought the
graphical user interface The GUI ( "UI" by itself is still usually pronounced . or ), graphical user interface, is a form of user interface that allows users to interact with electronic devices through graphical icons and audio indicator such as primary notation, ins ...
(GUI) concept to a wider audience and suggested the future belonged to machines with a GUI. The Lisa, however, cost $9,995, as it was packed with support chips, large amounts of memory, and a
hard disk drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with mag ...
, all very expensive then. The engineers then began studying all of the CPU designs available. Their conclusion about the existing 16-bit designs was that they were a lot more expensive and were still "a bit crap", offering only slightly higher performance than their BBC Micro design. They also almost always demanded a large number of support chips to operate even at that level, which drove up the cost of the computer as a whole. These systems would simply not hit the design goal. They also considered the new 32-bit designs, but these cost even more and had the same issues with support chips. According to
Sophie Wilson Sophie Mary Wilson (born Roger Wilson; June 1957) is an English computer scientist, who helped design the BBC Micro and ARM architecture. Wilson first designed a microcomputer during a break from studies at Selwyn College, Cambridge. She ...
, all the processors tested at that time performed about the same, with about a 4 Mbit/second bandwidth. Two key events led Acorn down the path to ARM. One was the publication of a series of reports from the
University of California, Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public land-grant research university in Berkeley, California. Established in 1868 as the University of California, it is the state's first land-grant un ...
, which suggested that a simple chip design could nevertheless have extremely high performance, much higher than the latest 32-bit designs on the market. The second was a visit by
Steve Furber Stephen Byram Furber (born 21 March 1953) is a British computer scientist, mathematician and hardware engineer, currently the ICL Professor of Computer Engineering in the Department of Computer Science at the University of Manchester, UK. A ...
and Sophie Wilson to the
Western Design Center The Western Design Center (WDC), located in Mesa, Arizona, is a company which develops intellectual property for, and licenses manufacture of, MOS Technology 65xx based microprocessors, microcontrollers (µCs), and related support devices. W ...
, a company run by
Bill Mensch William David Mensch, Jr. (born February 9, 1945) is an American electrical engineer born in Quakertown, Pennsylvania. He was a major contributor to the design of the Motorola 6800 8-bit microprocessor and was part of the team led by Chuck Pedd ...
and his sister, which had become the logical successor to the MOS team and was offering new versions like the WDC 65C02. The Acorn team saw high school students producing chip layouts on Apple II machines, which suggested that anyone could do it. In contrast, a visit to another design firm working on modern 32-bit CPU revealed a team with over a dozen members which were already on revision H of their design and yet it still contained bugs. This cemented their late 1983 decision to begin their own CPU design, the Acorn RISC Machine.


Design concepts

The original Berkeley RISC designs were in some sense teaching systems, not designed specifically for outright performance. To the RISC's basic register-heavy and load/store concepts, ARM added a number of the well-received design notes of the 6502. Primary among them was the ability to quickly serve interrupts, which allowed the machines to offer reasonable
input/output In computing, input/output (I/O, or informally io or IO) is the communication between an information processing system, such as a computer, and the outside world, possibly a human or another information processing system. Inputs are the signals ...
performance with no added external hardware. To offer interrupts with similar performance as the 6502, the ARM design limited its physical
address space In computing, an address space defines a range of discrete addresses, each of which may correspond to a network host, peripheral device, disk sector, a memory cell or other logical or physical entity. For software programs to save and retrieve s ...
to 64 MB of total addressable space, requiring 26 bits of address. As instructions were 4 bytes (32 bits) long, and required to be aligned on 4-byte boundaries, the lower 2 bits of an instruction address were always zero. This meant the
program counter The program counter (PC), commonly called the instruction pointer (IP) in Intel x86 and Itanium microprocessors, and sometimes called the instruction address register (IAR), the instruction counter, or just part of the instruction sequencer, i ...
(PC) only needed to be 24 bits, allowing it to be stored along with the eight bit
processor flag A status register, flag register, or condition code register (CCR) is a collection of status flag bits for a processor. Examples of such registers include FLAGS register in the x86 architecture, flags in the program status word (PSW) register in ...
s in a single 32-bit register. That meant that upon receiving an interrupt, the entire machine state could be saved in a single operation, whereas had the PC been a full 32-bit value, it would require separate operations to store the PC and the status flags. This decision halved the interrupt overhead. Another change, and among the most important in terms of practical real-world performance, was the modification of the
instruction set In computer science, an instruction set architecture (ISA), also called computer architecture, is an abstract model of a computer. A device that executes instructions described by that ISA, such as a central processing unit (CPU), is called an ...
to take advantage of
page mode DRAM Dynamic random-access memory (dynamic RAM or DRAM) is a type of random-access semiconductor memory that stores each bit of data in a memory cell, usually consisting of a tiny capacitor and a transistor, both typically based on metal-oxide ...
. Recently introduced, page mode allowed subsequent accesses of memory to run twice as fast if they were roughly in the same location, or "page", in the DRAM chip. Berkeley's design did not consider page mode and treated all memory equally. The ARM design added special vector-like memory access instructions, the "S-cycles", that could be used to fill or save multiple registers in a single page using page mode. This doubled memory performance when they could be used, and was especially important for graphics performance. The Berkeley RISC designs used
register window In computer engineering, register windows are a feature which dedicates registers to a subroutine by dynamically aliasing a subset of internal registers to fixed, programmer-visible registers. Register windows are implemented to improve the perfo ...
s to reduce the number of register saves and restores performed in procedure calls; the ARM design did not adopt this. Wilson developed the instruction set, writing a simulation of the processor in BBC BASIC that ran on a BBC Micro with a second 6502 processor. This convinced Acorn engineers they were on the right track. Wilson approached Acorn's CEO,
Hermann Hauser Hermann Maria Hauser, KBE, FRS, FREng, FInstP, CPhys (born 1948) is an Austrian-born entrepreneur, venture capitalist and inventor who is primarily associated with the Cambridge technology community in England. Education and early life W ...
, and requested more resources. Hauser gave his approval and assembled a small team to design the actual processor based on Wilson's ISA. The official Acorn RISC Machine project started in October 1983.


ARM1

Acorn chose VLSI Technology as the "silicon partner", as they were a source of ROMs and custom chips for Acorn. Acorn provided the design and VLSI provided the layout and production. The first samples of ARM silicon worked properly when first received and tested on 26 April 1985. Known as ARM1, these versions ran at 6 MHz. The first ARM application was as a second processor for the BBC Micro, where it helped in developing simulation software to finish development of the support chips (VIDC, IOC, MEMC), and sped up the CAD software used in ARM2 development. Wilson subsequently rewrote BBC BASIC in ARM
assembly language In computer programming, assembly language (or assembler language, or symbolic machine code), often referred to simply as Assembly and commonly abbreviated as ASM or asm, is any low-level programming language with a very strong correspondence b ...
. The in-depth knowledge gained from designing the instruction set enabled the code to be very dense, making ARM BBC BASIC an extremely good test for any ARM emulator.


ARM2

The result of the simulations on the ARM1 boards led to the late 1986 introduction of the ARM2 design running at 8 MHz, and the early 1987 speed-bumped version at 10 to 12 MHz. A significant change in the underlying architecture was the addition of a Booth multiplier, whereas formerly multiplication had to be carried out in software. Further, a new Fast Interrupt reQuest mode, FIQ for short, allowed registers 8 through 14 to be replaced as part of the interrupt itself. This meant FIQ requests did not have to save out their registers, further speeding interrupts. The ARM2 was roughly seven times the performance of a typical 7 MHz 68000-based system like the Commodore Amiga or
Macintosh SE The Macintosh SE is a personal computer designed, manufactured, and sold by Apple Computer, from March 1987 to October 1990. It marked a significant improvement on the Macintosh Plus design and was introduced by Apple at the same time as the Ma ...
. It was twice as fast as an
Intel 80386 The Intel 386, originally released as 80386 and later renamed i386, is a 32-bit microprocessor introduced in 1985. The first versions had 275,000 transistorsVAX-11/784 superminicomputer. The only systems that beat it were the
Sun SPARC SPARC (Scalable Processor Architecture) is a reduced instruction set computer (RISC) instruction set architecture originally developed by Sun Microsystems. Its design was strongly influenced by the experimental Berkeley RISC system developed in ...
and
MIPS R2000 The R2000 is a 32-bit microprocessor chip set developed by MIPS Computer Systems that implemented the MIPS I instruction set architecture (ISA). Introduced in January 1986, it was the first commercial implementation of the MIPS architecture and the ...
RISC-based
workstation A workstation is a special computer designed for technical or scientific applications. Intended primarily to be used by a single user, they are commonly connected to a local area network and run multi-user operating systems. The term ''workst ...
s. Further, as the CPU was designed for high-speed I/O, it dispensed with many of the support chips seen in these machines; notably, it lacked any dedicated
direct memory access Direct memory access (DMA) is a feature of computer systems and allows certain hardware subsystems to access main system memory independently of the central processing unit (CPU). Without DMA, when the CPU is using programmed input/output, it is ...
(DMA) controller which was often found on workstations. The graphics system was also simplified based on the same set of underlying assumptions about memory and timing. The result was a dramatically simplified design, offering performance on par with expensive workstations but at a price point similar to contemporary desktops. The ARM2 featured a
32-bit In computer architecture, 32-bit computing refers to computer systems with a processor, memory, and other major system components that operate on data in 32- bit units. Compared to smaller bit widths, 32-bit computers can perform large calculati ...
data bus In computer architecture, a bus (shortened form of the Latin '' omnibus'', and historically also called data highway or databus) is a communication system that transfers data between components inside a computer, or between computers. This ...
,
26-bit In computer architecture, 26-bit integers, memory addresses, or other data units are those that are 26 bits wide, and thus can represent unsigned values up to 67,108,863. Two examples of computer processors that featured 26-bit memory address ...
address space and 27 32-bit registers, of which 16 are accessible at any one time (including the PC). The ARM2 had a
transistor count The transistor count is the number of transistors in an electronic device (typically on a single substrate or "chip"). It is the most common measure of integrated circuit complexity (although the majority of transistors in modern microprocessors ...
of just 30,000, compared to Motorola's six-year-older 68000 model with around 68,000. Much of this simplicity came from the lack of
microcode In processor design, microcode (μcode) is a technique that interposes a layer of computer organization between the central processing unit (CPU) hardware and the programmer-visible instruction set architecture of a computer. Microcode is a la ...
, which represents about one-quarter to one-third of the 68000's transistors, and the lack of (like most CPUs of the day) a cache. This simplicity enabled the ARM2 to have low power consumption, yet offer better performance than the
Intel 80286 The Intel 80286 (also marketed as the iAPX 286 and often called Intel 286) is a 16-bit microprocessor that was introduced on February 1, 1982. It was the first 8086-based CPU with separate, non- multiplexed address and data buses and also the ...
. A successor, ARM3, was produced with a 4 KB cache, which further improved performance. The address bus was extended to 32 bits in the ARM6, but program code still had to lie within the first 64 MB of memory in 26-bit compatibility mode, due to the reserved bits for the status flags.


Advanced RISC Machines Ltd. – ARM6

In the late 1980s,
Apple Computer Apple Inc. is an American multinational technology company headquartered in Cupertino, California, United States. Apple is the largest technology company by revenue (totaling in 2021) and, as of June 2022, is the world's biggest company ...
and VLSI Technology started working with Acorn on newer versions of the ARM core. In 1990, Acorn spun off the design team into a new company named Advanced RISC Machines Ltd., which became ARM Ltd. when its parent company,
Arm Holdings Arm is a British semiconductor and software design company based in Cambridge, England. Its primary business is in the design of ARM processors (CPUs). It also designs other chips, provides software development tools under the DS-5, RealView ...
plc, floated on the
London Stock Exchange London Stock Exchange (LSE) is a stock exchange in the City of London, England, United Kingdom. , the total market value of all companies trading on LSE was £3.9 trillion. Its current premises are situated in Paternoster Square close to St Pau ...
and
NASDAQ The Nasdaq Stock Market () (National Association of Securities Dealers Automated Quotations Stock Market) is an American stock exchange based in New York City. It is the most active stock trading venue in the US by volume, and ranked second ...
in 1998. The new Apple-ARM work would eventually evolve into the ARM6, first released in early 1992. Apple used the ARM6-based ARM610 as the basis for their
Apple Newton The Newton is a series of personal digital assistants (PDAs) developed and marketed by Apple Computer, Inc. An early device in the PDA category (the Newton originated the term), it was the first to feature handwriting recognition. Apple started ...
PDA.


Early licensees

In 1994, Acorn used the ARM610 as the main
central processing unit A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, a ...
(CPU) in their RiscPC computers. DEC licensed the ARMv4 architecture and produced the StrongARM. At 233  MHz, this CPU drew only one watt (newer versions draw far less). This work was later passed to Intel as part of a lawsuit settlement, and Intel took the opportunity to supplement their i960 line with the StrongARM. Intel later developed its own high performance implementation named XScale, which it has since sold to Marvell. Transistor count of the ARM core remained essentially the same throughout these changes; ARM2 had 30,000 transistors, while ARM6 grew only to 35,000.


Market share

In 2005, about 98% of all mobile phones sold used at least one ARM processor. In 2010, producers of chips based on ARM architectures reported shipments of 6.1 billion ARM-based processors, representing 95% of
smartphone A smartphone is a portable computer device that combines mobile telephone and computing functions into one unit. They are distinguished from feature phones by their stronger hardware capabilities and extensive mobile operating systems, whi ...
s, 35% of
digital television Digital television (DTV) is the transmission of television signals using digital encoding, in contrast to the earlier analog television technology which used analog signals. At the time of its development it was considered an innovative adva ...
s and
set-top box A set-top box (STB), also colloquially known as a cable box and historically television decoder, is an information appliance device that generally contains a TV-tuner input and displays output to a television set and an external source of s ...
es, and 10% of mobile computers. In 2011, the 32-bit ARM architecture was the most widely used architecture in mobile devices and the most popular 32-bit one in embedded systems. In 2013, 10 billion were produced and "ARM-based chips are found in nearly 60 percent of the world's mobile devices".


Licensing


Core licence

Arm Ltd.'s primary business is selling IP cores, which licensees use to create
microcontroller A microcontroller (MCU for ''microcontroller unit'', often also MC, UC, or μC) is a small computer on a single VLSI integrated circuit (IC) chip. A microcontroller contains one or more CPUs ( processor cores) along with memory and programmabl ...
s (MCUs),
CPU A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, a ...
s, and systems-on-chips based on those cores. The
original design manufacturer An original design manufacturer is a company that designs and manufactures a product that is eventually rebranded by another firm for sale. Such companies allow the firm that owns or licenses the brand to produce products while having to engage i ...
combines the ARM core with other parts to produce a complete device, typically one that can be built in existing
semiconductor fabrication plant In the microelectronics industry, a semiconductor fabrication plant (commonly called a fab; sometimes foundry) is a factory where devices such as integrated circuits are manufactured. Fabs require many expensive devices to function. Estimates ...
s (fabs) at low cost and still deliver substantial performance. The most successful implementation has been the ARM7TDMI with hundreds of millions sold.
Atmel Atmel Corporation was a creator and manufacturer of semiconductors before being subsumed by Microchip Technology in 2016. Atmel was founded in 1984. The company focused on embedded systems built around microcontrollers. Its products included mi ...
has been a precursor design center in the ARM7TDMI-based embedded system. The ARM architectures used in smartphones, PDAs and other
mobile device A mobile device (or handheld computer) is a computer small enough to hold and operate in the hand. Mobile devices typically have a flat LCD or OLED screen, a touchscreen interface, and digital or physical buttons. They may also have a physica ...
s range from ARMv5 to . In 2009, some manufacturers introduced netbooks based on ARM architecture CPUs, in direct competition with netbooks based on
Intel Atom Intel Atom is the brand name for a line of IA-32 and x86-64 instruction set ultra-low-voltage processors by Intel Corporation designed to reduce electric consumption and power dissipation in comparison with ordinary processors of the Intel Co ...
. Arm Ltd. offers a variety of licensing terms, varying in cost and deliverables. Arm Ltd. provides to all licensees an integratable hardware description of the ARM core as well as complete software development toolset (
compiler In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs tha ...
, debugger,
software development kit A software development kit (SDK) is a collection of software development tools in one installable package. They facilitate the creation of applications by having a compiler, debugger and sometimes a software framework. They are normally specific ...
), and the right to sell manufactured
silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ...
containing the ARM CPU. SoC packages integrating ARM's core designs include Nvidia Tegra's first three generations, CSR plc's Quatro family, ST-Ericsson's Nova and NovaThor, Silicon Labs's Precision32 MCU, Texas Instruments's
OMAP The OMAP (Open Multimedia Applications Platform) family, developed by Texas Instruments, was a series of image/ video processors. They are proprietary system on chips (SoCs) for portable and mobile multimedia applications. OMAP devices generally ...
products, Samsung's Hummingbird and
Exynos Exynos, formerly Hummingbird (), is a series of ARM-based system-on-chips developed by Samsung Electronics' System LSI division and manufactured by Samsung Foundry. It is a continuation of Samsung's earlier S3C, S5L and S5P line of SoCs. E ...
products, Apple's A4, A5, and A5X, and
NXP NXP Semiconductors N.V. (NXP) is a Dutch semiconductor designer and manufacturer with headquarters in Eindhoven, Netherlands. The company employs approximately 31,000 people in more than 30 countries. NXP reported revenue of $11.06 billion in 2 ...
's i.MX. Fabless licensees, who wish to integrate an ARM core into their own chip design, are usually only interested in acquiring a ready-to-manufacture verified
semiconductor intellectual property core In electronic design, a semiconductor intellectual property core (SIP core), IP core, or IP block is a reusable unit of logic, cell, or integrated circuit layout design that is the intellectual property of one party. IP cores can be licensed t ...
. For these customers, Arm Ltd. delivers a gate netlist description of the chosen ARM core, along with an abstracted simulation model and test programs to aid design integration and verification. More ambitious customers, including integrated device manufacturers (IDM) and foundry operators, choose to acquire the processor IP in synthesizable RTL ( Verilog) form. With the synthesizable RTL, the customer has the ability to perform architectural level optimisations and extensions. This allows the designer to achieve exotic design goals not otherwise possible with an unmodified netlist ( high clock speed, very low power consumption, instruction set extensions, etc.). While Arm Ltd. does not grant the licensee the right to resell the ARM architecture itself, licensees may freely sell manufactured products such as chip devices, evaluation boards and complete systems. Merchant foundries can be a special case; not only are they allowed to sell finished silicon containing ARM cores, they generally hold the right to re-manufacture ARM cores for other customers. Arm Ltd. prices its IP based on perceived value. Lower performing ARM cores typically have lower licence costs than higher performing cores. In implementation terms, a synthesisable core costs more than a hard macro (blackbox) core. Complicating price matters, a merchant foundry that holds an ARM licence, such as Samsung or Fujitsu, can offer fab customers reduced licensing costs. In exchange for acquiring the ARM core through the foundry's in-house design services, the customer can reduce or eliminate payment of ARM's upfront licence fee. Compared to dedicated semiconductor foundries (such as
TSMC Taiwan Semiconductor Manufacturing Company Limited (TSMC; also called Taiwan Semiconductor) is a Taiwanese multinational semiconductor contract manufacturing and design company. It is the world's most valuable semiconductor company, the world' ...
and UMC) without in-house design services, Fujitsu/Samsung charge two- to three-times more per manufactured
wafer A wafer is a crisp, often sweet, very thin, flat, light and dry biscuit, often used to decorate ice cream, and also used as a garnish on some sweet dishes. Wafers can also be made into cookies with cream flavoring sandwiched between them. They ...
. For low to mid volume applications, a design service foundry offers lower overall pricing (through subsidisation of the licence fee). For high volume mass-produced parts, the long term cost reduction achievable through lower wafer pricing reduces the impact of ARM's NRE ( non-recurring engineering) costs, making the dedicated foundry a better choice. Companies that have developed chips with cores designed by Arm include Amazon.com's
Annapurna Labs Annapurna Labs is an Israeli microelectronics company. Since January 2015 it has been a subsidiary of Amazon.com. Amazon reportedly acquired the company for its Amazon Web Services division for US$350–370M. History Annapurna Labs, named after t ...
subsidiary,
Analog Devices Analog Devices, Inc. (ADI), also known simply as Analog, is an American multinational semiconductor company specializing in data conversion, signal processing and power management technology, headquartered in Wilmington, Massachusetts. The ...
,
Apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple trees are cultivated worldwide and are the most widely grown species in the genus '' Malus''. The tree originated in Central Asia, where its wild ancest ...
,
AppliedMicro Applied Micro Circuits Corporation (also known as AppliedMicro, AMCC or APM) was a fabless semiconductor company designing network and embedded Power ISA (including a Power ISA license), and server processor ARM (including an ARMv8-A license), ...
(now: MACOM Technology Solutions),
Atmel Atmel Corporation was a creator and manufacturer of semiconductors before being subsumed by Microchip Technology in 2016. Atmel was founded in 1984. The company focused on embedded systems built around microcontrollers. Its products included mi ...
, Broadcom, Cavium,
Cypress Semiconductor Cypress Semiconductor was an American semiconductor design and manufacturing company. It offered NOR flash memories, F-RAM and SRAM Traveo microcontrollers, PSoC programmable system-on-chip solutions, analog and PMIC Power Management ICs, Ca ...
,
Freescale Semiconductor Freescale Semiconductor, Inc. was an American semiconductor manufacturer. It was created by the divestiture of the Semiconductor Products Sector of Motorola in 2004. Freescale focused their integrated circuit products on the automotive, em ...
(now
NXP Semiconductors NXP Semiconductors N.V. (NXP) is a Dutch semiconductor designer and manufacturer with headquarters in Eindhoven, Netherlands. The company employs approximately 31,000 people in more than 30 countries. NXP reported revenue of $11.06 billion in 2 ...
),
Huawei Huawei Technologies Co., Ltd. ( ; ) is a Chinese multinational technology corporation headquartered in Shenzhen, Guangdong, China. It designs, develops, produces and sells telecommunications equipment, consumer electronics and various sma ...
,
Intel Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California. It is the world's largest semiconductor chip manufacturer by revenue, and is one of the developers of the x86 ser ...
, Maxim Integrated,
Nvidia Nvidia CorporationOfficially written as NVIDIA and stylized in its logo as VIDIA with the lowercase "n" the same height as the uppercase "VIDIA"; formerly stylized as VIDIA with a large italicized lowercase "n" on products from the mid 1990s to ...
,
NXP NXP Semiconductors N.V. (NXP) is a Dutch semiconductor designer and manufacturer with headquarters in Eindhoven, Netherlands. The company employs approximately 31,000 people in more than 30 countries. NXP reported revenue of $11.06 billion in 2 ...
,
Qualcomm Qualcomm () is an American multinational corporation headquartered in San Diego, California, and incorporated in Delaware. It creates semiconductors, software, and services related to wireless technology. It owns patents critical to the 5G, ...
,
Renesas is a Japanese semiconductor manufacturer headquartered in Tokyo, Japan, initially incorporated in 2002 as Renesas Technology, the consolidated entity of the semiconductor units of Hitachi and Mitsubishi excluding their dynamic random-access memo ...
,
Samsung Electronics Samsung Electronics Co., Ltd. (, sometimes shortened to SEC and stylized as SΛMSUNG) is a South Korean multinational electronics corporation headquartered in Yeongtong-gu, Suwon, South Korea. It is the pinnacle of the Samsung chaebol, acc ...
, ST Microelectronics,
Texas Instruments Texas Instruments Incorporated (TI) is an American technology company headquartered in Dallas, Texas, that designs and manufactures semiconductors and various integrated circuits, which it sells to electronics designers and manufacturers globa ...
, and
Xilinx Xilinx, Inc. ( ) was an American technology and semiconductor company that primarily supplied programmable logic devices. The company was known for inventing the first commercially viable field-programmable gate array (FPGA) and creating the fi ...
.


Built on ARM Cortex Technology licence

In February 2016, ARM announced the Built on ARM Cortex Technology licence, often shortened to Built on Cortex (BoC) licence. This licence allows companies to partner with ARM and make modifications to ARM Cortex designs. These design modifications will not be shared with other companies. These semi-custom core designs also have brand freedom, for example Kryo 280. Companies that are current licensees of Built on ARM Cortex Technology include
Qualcomm Qualcomm () is an American multinational corporation headquartered in San Diego, California, and incorporated in Delaware. It creates semiconductors, software, and services related to wireless technology. It owns patents critical to the 5G, ...
.


Architectural licence

Companies can also obtain an ARM ''architectural licence'' for designing their own CPU cores using the ARM instruction sets. These cores must comply fully with the ARM architecture. Companies that have designed cores that implement an ARM architecture include Apple, AppliedMicro (now: Ampere Computing), Broadcom, Cavium (now: Marvell),
Digital Equipment Corporation Digital Equipment Corporation (DEC ), using the trademark Digital, was a major American company in the computer industry from the 1960s to the 1990s. The company was co-founded by Ken Olsen and Harlan Anderson in 1957. Olsen was president un ...
, Intel, Nvidia, Qualcomm, Samsung Electronics,
Fujitsu is a Japanese multinational information and communications technology equipment and services corporation, established in 1935 and headquartered in Tokyo. Fujitsu is the world's sixth-largest IT services provider by annual revenue, and the la ...
, and NUVIA Inc. (acquired by Qualcomm in 2021).


ARM Flexible Access

On 16 July 2019, ARM announced ARM Flexible Access. ARM Flexible Access provides unlimited access to included ARM
intellectual property Intellectual property (IP) is a category of property that includes intangible creations of the human intellect. There are many types of intellectual property, and some countries recognize more than others. The best-known types are patents, co ...
(IP) for development. Per product licence fees are required once a customer reaches foundry tapeout or prototyping. 75% of ARM's most recent IP over the last two years are included in ARM Flexible Access. As of October 2019: * CPUs: Cortex-A5,
Cortex-A7 The ARM Cortex-A7 MPCore is a 32-bit microprocessor core licensed by ARM Holdings implementing the ARMv7-A architecture announced in 2011. Overview It has two target applications; firstly as a smaller, simpler, and more power-efficient success ...
, Cortex-A32, Cortex-A34, Cortex-A35, Cortex-A53, Cortex-R5, Cortex-R8, Cortex-R52,
Cortex-M0 The ARM Cortex-M is a group of 32-bit RISC ARM processor cores licensed by Arm Holdings. These cores are optimized for low-cost and energy-efficient integrated circuits, which have been embedded in tens of billions of consumer devices. Though ...
, Cortex-M0+, Cortex-M3, Cortex-M4,
Cortex-M7 The ARM Cortex-M is a group of 32-bit RISC ARM processor cores licensed by Arm Holdings. These cores are optimized for low-cost and energy-efficient integrated circuits, which have been embedded in tens of billions of consumer devices. Though ...
,
Cortex-M23 The ARM Cortex-M is a group of 32-bit RISC ARM processor cores licensed by Arm Holdings. These cores are optimized for low-cost and energy-efficient integrated circuits, which have been embedded in tens of billions of consumer devices. Though ...
, Cortex-M33 * GPUs: Mali-G52, Mali-G31. Includes Mali Driver Development Kits (DDK). * Interconnect: CoreLink NIC-400, CoreLink NIC-450, CoreLink CCI-400, CoreLink CCI-500, CoreLink CCI-550, ADB-400 AMBA, XHB-400 AXI-AHB * System Controllers: CoreLink GIC-400, CoreLink GIC-500, PL192 VIC, BP141 TrustZone Memory Wrapper, CoreLink TZC-400, CoreLink L2C-310, CoreLink MMU-500, BP140 Memory Interface * Security IP: CryptoCell-312, CryptoCell-712, TrustZone True Random Number Generator * Peripheral Controllers: PL011 UART, PL022 SPI, PL031 RTC * Debug & Trace: CoreSight SoC-400, CoreSight SDC-600, CoreSight STM-500, CoreSight System Trace Macrocell, CoreSight Trace Memory Controller * Design Kits: Corstone-101, Corstone-201 * Physical IP: Artisan PIK for Cortex-M33 TSMC 22ULL including memory compilers, logic libraries, GPIOs and documentation * Tools & Materials: Socrates IP ToolingARM Design Studio, Virtual System Models * Support: Standard ARM Technical support, ARM online training, maintenance updates, credits toward onsite training and design reviews


Cores

Arm provides a list of vendors who implement ARM cores in their design (application specific standard products (ASSP), microprocessor and microcontrollers).


Example applications of ARM cores

ARM cores are used in a number of products, particularly
PDA PDA may refer to: Science and technology * Patron-driven acquisition, a mechanism for libraries to purchase books *Personal digital assistant, a mobile device * Photodiode array, a type of detector * Polydiacetylenes, a family of conducting po ...
s and
smartphone A smartphone is a portable computer device that combines mobile telephone and computing functions into one unit. They are distinguished from feature phones by their stronger hardware capabilities and extensive mobile operating systems, whi ...
s. Some
computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes, and development of both hardware and software. Computing has scientific, ...
examples are
Microsoft Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washi ...
's first generation Surface, Surface 2 and
Pocket PC A Pocket PC (P/PC, PPC) is a class of personal digital assistant (PDA) that runs the Windows Mobile or Windows Embedded Compact operating system that has some of the abilities of modern desktop PCs. The name was introduced by Microsoft in 200 ...
devices (following
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),
Apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple trees are cultivated worldwide and are the most widely grown species in the genus '' Malus''. The tree originated in Central Asia, where its wild ancest ...
's
iPad The iPad is a brand of iOS and iPadOS-based tablet computers that are developed by Apple Inc., Apple Inc. The iPad was conceived before the related iPhone but the iPhone was developed and released first. Speculation about the development, ...
s, and Asus's Eee Pad Transformer
tablet computer A tablet computer, commonly shortened to tablet, is a mobile device, typically with a mobile operating system and touchscreen display processing circuitry, and a rechargeable battery in a single, thin and flat package. Tablets, being com ...
s, and several
Chromebook A Chromebook (sometimes stylized in lowercase as chromebook) is a laptop or tablet running the Linux-based ChromeOS as its operating system. Initially designed to heavily rely on web applications for tasks using the Google Chrome browser, Chrome ...
laptops. Others include Apple's iPhone
smartphone A smartphone is a portable computer device that combines mobile telephone and computing functions into one unit. They are distinguished from feature phones by their stronger hardware capabilities and extensive mobile operating systems, whi ...
s and
iPod The iPod is a discontinued series of portable media players and multi-purpose mobile devices designed and marketed by Apple Inc. The first version was released on October 23, 2001, about months after the Macintosh version of iTunes wa ...
portable media player A portable media player (PMP) (also including the related digital audio player (DAP)) is a portable consumer electronics device capable of storing and playing digital media such as audio, images, and video files. The data is typically stored o ...
s, Canon PowerShot
digital camera A digital camera is a camera that captures photographs in digital memory. Most cameras produced today are digital, largely replacing those that capture images on photographic film. Digital cameras are now widely incorporated into mobile devices ...
s,
Nintendo Switch The is a hybrid video game console developed by Nintendo and released worldwide in most regions on March 3, 2017. The console itself is a tablet that can either be docked for use as a home console or used as a portable device, making it a ...
hybrid, the
Wii The Wii ( ) is a home video game console developed and marketed by Nintendo. It was released on November 19, 2006, in North America and in December 2006 for most other regions of the world. It is Nintendo's fifth major home game console, ...
security processor and 3DS
handheld game console A handheld game console, or simply handheld console, is a small, portable self-contained video game console with a built-in screen, game controls and speakers. Handheld game consoles are smaller than home video game consoles and contain the co ...
s, and
TomTom TomTom N.V. is a Dutch multinational developer and creator of location technology and consumer electronics. Founded in 1991 and headquartered in Amsterdam, TomTom released its first generation of satellite navigation devices to market in 2004 ...
turn-by-turn navigation systems. In 2005, Arm took part in the development of
Manchester University , mottoeng = Knowledge, Wisdom, Humanity , established = 2004 – University of Manchester Predecessor institutions: 1956 – UMIST (as university college; university 1994) 1904 – Victoria University of Manchester 1880 – Victoria Univer ...
's computer
SpiNNaker A spinnaker is a sail designed specifically for sailing off the wind on courses between a reach (wind at 90° to the course) to downwind (course in the same direction as the wind). Spinnakers are constructed of lightweight fabric, usually ny ...
, which used ARM cores to simulate the
human brain The human brain is the central organ of the human nervous system, and with the spinal cord makes up the central nervous system. The brain consists of the cerebrum, the brainstem and the cerebellum. It controls most of the activities of ...
. ARM chips are also used in Raspberry Pi, BeagleBoard, BeagleBone,
PandaBoard The PandaBoard was a low-power single-board computer development platform based on the Texas Instruments OMAP4430 system on a chip (SoC). The board has been available to the public at the subsidized price of US$174 since 27 October 2010. It is ...
, and other
single-board computer A single-board computer (SBC) is a complete computer built on a single circuit board, with microprocessor(s), memory, input/output (I/O) and other features required of a functional computer. Single-board computers are commonly made as demonstrat ...
s, because they are very small, inexpensive, and consume very little power.


32-bit architecture

The 32-bit ARM architecture (ARM32), such as Armv7-A (implementing AArch32; see section on Armv8-A for more on it), was the most widely used architecture in mobile devices . Since 1995, various versions of the ''ARM Architecture Reference Manual'' (see ) have been the primary source of documentation on the ARM processor architecture and instruction set, distinguishing interfaces that all ARM processors are required to support (such as instruction semantics) from implementation details that may vary. The architecture has evolved over time, and version seven of the architecture, ARMv7, defines three architecture "profiles": * A-profile, the "Application" profile, implemented by 32-bit cores in the
Cortex-A The ARM Cortex-A is a group of 32-bit and 64-bit RISC ARM processor cores licensed by Arm Holdings. The cores are intended for application use. The group consists of 32-bit only cores: ARM Cortex-A5, ARM Cortex-A7, ARM Cortex-A8, ARM Cortex-A9, ...
series and by some non-ARM cores * R-profile, the "Real-time" profile, implemented by cores in the Cortex-R series * M-profile, the "Microcontroller" profile, implemented by most cores in the
Cortex-M The ARM Cortex-M is a group of 32-bit RISC ARM processor cores licensed by Arm Holdings. These cores are optimized for low-cost and energy-efficient integrated circuits, which have been embedded in tens of billions of consumer devices. Though ...
series Although the architecture profiles were first defined for ARMv7, ARM subsequently defined the ARMv6-M architecture (used by the Cortex M0/ M0+/ M1) as a subset of the ARMv7-M profile with fewer instructions.


CPU modes

Except in the M-profile, the 32-bit ARM architecture specifies several CPU modes, depending on the implemented architecture features. At any moment in time, the CPU can be in only one mode, but it can switch modes due to external events (interrupts) or programmatically. * ''User mode:'' The only non-privileged mode. * ''FIQ mode:'' A privileged mode that is entered whenever the processor accepts a
fast interrupt request Fast interrupt request (FIQ) is a specialized type of interrupt request, which is a standard technique used in computer CPUs to deal with events that need to be processed as they occur, such as receiving data from a network card, or keyboard or mo ...
. * ''IRQ mode:'' A privileged mode that is entered whenever the processor accepts an interrupt. * ''Supervisor (svc) mode:'' A privileged mode entered whenever the CPU is reset or when an SVC instruction is executed. * ''Abort mode:'' A privileged mode that is entered whenever a prefetch abort or data abort exception occurs. * ''Undefined mode:'' A privileged mode that is entered whenever an undefined instruction exception occurs. * ''System mode (ARMv4 and above):'' The only privileged mode that is not entered by an exception. It can only be entered by executing an instruction that explicitly writes to the mode bits of the Current Program Status Register (CPSR) from another privileged mode (not from user mode). * ''Monitor mode (ARMv6 and ARMv7 Security Extensions, ARMv8 EL3):'' A monitor mode is introduced to support TrustZone extension in ARM cores. * ''Hyp mode (ARMv7 Virtualization Extensions, ARMv8 EL2):'' A hypervisor mode that supports
Popek and Goldberg virtualization requirements The Popek and Goldberg virtualization requirements are a set of conditions sufficient for a computer architecture to support system virtualization efficiently. They were introduced by Gerald J. Popek and Robert P. Goldberg in their 1974 article "F ...
for the non-secure operation of the CPU. * ''Thread mode (ARMv6-M, ARMv7-M, ARMv8-M):'' A mode which can be specified as either privileged or unprivileged. Whether the Main Stack Pointer (MSP) or Process Stack Pointer (PSP) is used can also be specified in CONTROL register with privileged access. This mode is designed for user tasks in RTOS environment but it's typically used in bare-metal for super-loop. * ''Handler mode (ARMv6-M, ARMv7-M, ARMv8-M):'' A mode dedicated for exception handling (except the RESET which are handled in Thread mode). Handler mode always uses MSP and works in privileged level.


Instruction set

The original (and subsequent) ARM implementation was hardwired without
microcode In processor design, microcode (μcode) is a technique that interposes a layer of computer organization between the central processing unit (CPU) hardware and the programmer-visible instruction set architecture of a computer. Microcode is a la ...
, like the much simpler
8-bit In computer architecture, 8-bit integers or other data units are those that are 8 bits wide (1 octet). Also, 8-bit central processing unit (CPU) and arithmetic logic unit (ALU) architectures are those that are based on registers or data buses ...
6502 processor used in prior Acorn microcomputers. The 32-bit ARM architecture (and the 64-bit architecture for the most part) includes the following RISC features: * Load–store architecture. * No support for unaligned memory accesses in the original version of the architecture. ARMv6 and later, except some microcontroller versions, support unaligned accesses for half-word and single-word load/store instructions with some limitations, such as no guaranteed atomicity. * Uniform 16 × 32-bit
register file A register file is an array of processor registers in a central processing unit (CPU). Register banking is the method of using a single name to access multiple different physical registers depending on the operating mode. Modern integrated circuit- ...
(including the program counter, stack pointer and the link register). * Fixed instruction width of 32 bits to ease decoding and pipelining, at the cost of decreased
code density In computer science, an instruction set architecture (ISA), also called computer architecture, is an abstract model of a computer. A device that executes instructions described by that ISA, such as a central processing unit (CPU), is called an ...
. Later, the Thumb instruction set added 16-bit instructions and increased code density. * Mostly single clock-cycle execution. To compensate for the simpler design, compared with processors like the Intel 80286 and Motorola 68020, some additional design features were used: * Conditional execution of most instructions reduces branch overhead and compensates for the lack of a
branch predictor In computer architecture, a branch predictor is a digital circuit that tries to guess which way a branch (e.g., an if–then–else structure) will go before this is known definitively. The purpose of the branch predictor is to improve the flow ...
in early chips. * Arithmetic instructions alter condition codes only when desired. * 32-bit
barrel shifter A barrel shifter is a digital circuit that can shift a data word by a specified number of bits without the use of any sequential logic, only pure combinational logic, i.e. it inherently provides a binary operation. It can however in theory also ...
can be used without performance penalty with most arithmetic instructions and address calculations. * Has powerful indexed addressing modes. * A
link register A link register (LR for short) is a register which holds the address to return to when a subroutine call completes. This is more efficient than the more traditional scheme of storing return addresses on a call stack, sometimes called a machine s ...
supports fast leaf function calls. * A simple, but fast, 2-priority-level interrupt subsystem has switched register banks.


Arithmetic instructions

ARM includes integer arithmetic operations for add, subtract, and multiply; some versions of the architecture also support divide operations. ARM supports 32-bit × 32-bit multiplies with either a 32-bit result or 64-bit result, though Cortex-M0 / M0+ / M1 cores don't support 64-bit results.Cortex-M0 r0p0 Technical Reference Manual; Arm Holdings.
/ref> Some ARM cores also support 16-bit × 16-bit and 32-bit × 16-bit multiplies. The divide instructions are only included in the following ARM architectures: * Armv7-M and Armv7E-M architectures always include divide instructions. * Armv7-R architecture always includes divide instructions in the Thumb instruction set, but optionally in its 32-bit instruction set. * Armv7-A architecture optionally includes the divide instructions. The instructions might not be implemented, or implemented only in the Thumb instruction set, or implemented in both the Thumb and ARM instruction sets, or implemented if the Virtualization Extensions are included.


Registers

Registers R0 through R7 are the same across all CPU modes; they are never banked. Registers R8 through R12 are the same across all CPU modes except FIQ mode. FIQ mode has its own distinct R8 through R12 registers. R13 and R14 are banked across all privileged CPU modes except system mode. That is, each mode that can be entered because of an exception has its own R13 and R14. These registers generally contain the stack pointer and the return address from function calls, respectively. Aliases: * R13 is also referred to as SP, the stack pointer. * R14 is also referred to as LR, the
link register A link register (LR for short) is a register which holds the address to return to when a subroutine call completes. This is more efficient than the more traditional scheme of storing return addresses on a call stack, sometimes called a machine s ...
. * R15 is also referred to as PC, the
program counter The program counter (PC), commonly called the instruction pointer (IP) in Intel x86 and Itanium microprocessors, and sometimes called the instruction address register (IAR), the instruction counter, or just part of the instruction sequencer, i ...
. The Current Program Status Register (CPSR) has the following 32 bits. * M (bits 0–4) is the processor mode bits. * T (bit 5) is the Thumb state bit. * F (bit 6) is the FIQ disable bit. * I (bit 7) is the IRQ disable bit. * A (bit 8) is the imprecise data abort disable bit. * E (bit 9) is the data endianness bit. * IT (bits 10–15 and 25–26) is the if-then state bits. * GE (bits 16–19) is the greater-than-or-equal-to bits. * DNM (bits 20–23) is the do not modify bits. * J (bit 24) is the Java state bit. * Q (bit 27) is the sticky overflow bit. * V (bit 28) is the overflow bit. * C (bit 29) is the carry/borrow/extend bit. * Z (bit 30) is the zero bit. * N (bit 31) is the negative/less than bit.


Conditional execution

Almost every ARM instruction has a conditional execution feature called predication, which is implemented with a 4-bit condition code selector (the predicate). To allow for unconditional execution, one of the four-bit codes causes the instruction to be always executed. Most other CPU architectures only have condition codes on branch instructions. Though the predicate takes up four of the 32 bits in an instruction code, and thus cuts down significantly on the encoding bits available for displacements in memory access instructions, it avoids branch instructions when generating code for small if statements. Apart from eliminating the branch instructions themselves, this preserves the fetch/decode/execute pipeline at the cost of only one cycle per skipped instruction. An algorithm that provides a good example of conditional execution is the subtraction-based
Euclidean algorithm In mathematics, the Euclidean algorithm,Some widely used textbooks, such as I. N. Herstein's ''Topics in Algebra'' and Serge Lang's ''Algebra'', use the term "Euclidean algorithm" to refer to Euclidean division or Euclid's algorithm, is an e ...
for computing the
greatest common divisor In mathematics, the greatest common divisor (GCD) of two or more integers, which are not all zero, is the largest positive integer that divides each of the integers. For two integers ''x'', ''y'', the greatest common divisor of ''x'' and ''y'' is ...
. In the
C programming language ''The C Programming Language'' (sometimes termed ''K&R'', after its authors' initials) is a computer programming book written by Brian Kernighan and Dennis Ritchie, the latter of whom originally designed and implemented the language, as well a ...
, the algorithm can be written as: int gcd(int a, int b) The same algorithm can be rewritten in a way closer to target ARM instructions as: loop: // Compare a and b GT = a > b; LT = a < b; NE = a != b; // Perform operations based on flag results if(GT) a -= b; // Subtract *only* if greater-than if(LT) b -= a; // Subtract *only* if less-than if(NE) goto loop; // Loop *only* if compared values were not equal return a; and coded in
assembly language In computer programming, assembly language (or assembler language, or symbolic machine code), often referred to simply as Assembly and commonly abbreviated as ASM or asm, is any low-level programming language with a very strong correspondence b ...
as: ; assign a to register r0, b to r1 loop: CMP r0, r1 ; set condition "NE" if (a != b), ; "GT" if (a > b), ; or "LT" if (a < b) SUBGT r0, r0, r1 ; if "GT" (Greater Than), then a = a-b SUBLT r1, r1, r0 ; if "LT" (Less Than), then b = b-a BNE loop ; if "NE" (Not Equal), then loop B lr ; return which avoids the branches around the then and else clauses. If r0 and r1 are equal then neither of the SUB instructions will be executed, eliminating the need for a conditional branch to implement the while check at the top of the loop, for example had SUBLE (less than or equal) been used. One of the ways that Thumb code provides a more dense encoding is to remove the four-bit selector from non-branch instructions.


Other features

Another feature of the
instruction set In computer science, an instruction set architecture (ISA), also called computer architecture, is an abstract model of a computer. A device that executes instructions described by that ISA, such as a central processing unit (CPU), is called an ...
is the ability to fold shifts and rotates into the ''data processing'' (arithmetic, logical, and register-register move) instructions, so that, for example, the statement in C language: a += (j << 2); could be rendered as a one-word, one-cycle instruction: ADD Ra, Ra, Rj, LSL #2 This results in the typical ARM program being denser than expected with fewer memory accesses; thus the pipeline is used more efficiently. The ARM processor also has features rarely seen in other RISC architectures, such as PC-relative addressing (indeed, on the 32-bit ARM the PC is one of its 16 registers) and pre- and post-increment addressing modes. The ARM instruction set has increased over time. Some early ARM processors (before ARM7TDMI), for example, have no instruction to store a two-byte quantity.


Pipelines and other implementation issues

The ARM7 and earlier implementations have a three-stage pipeline; the stages being fetch, decode, and execute. Higher-performance designs, such as the ARM9, have deeper pipelines: Cortex-A8 has thirteen stages. Additional implementation changes for higher performance include a faster adder and more extensive
branch prediction In computer architecture, a branch predictor is a digital circuit that tries to guess which way a branch (e.g., an if–then–else structure) will go before this is known definitively. The purpose of the branch predictor is to improve the flow ...
logic. The difference between the ARM7DI and ARM7DMI cores, for example, was an improved multiplier; hence the added "M".


Coprocessors

The ARM architecture (pre-Armv8) provides a non-intrusive way of extending the instruction set using "coprocessors" that can be addressed using MCR, MRC, MRRC, MCRR, and similar instructions. The coprocessor space is divided logically into 16 coprocessors with numbers from 0 to 15, coprocessor 15 (cp15) being reserved for some typical control functions like managing the caches and MMU operation on processors that have one. In ARM-based machines, peripheral devices are usually attached to the processor by mapping their physical registers into ARM memory space, into the coprocessor space, or by connecting to another device (a bus) that in turn attaches to the processor. Coprocessor accesses have lower latency, so some peripherals—for example, an XScale interrupt controller—are accessible in both ways: through memory and through coprocessors. In other cases, chip designers only integrate hardware using the coprocessor mechanism. For example, an image processing engine might be a small ARM7TDMI core combined with a coprocessor that has specialised operations to support a specific set of HDTV transcoding primitives.


Debugging

All modern ARM processors include hardware debugging facilities, allowing software debuggers to perform operations such as halting, stepping, and breakpointing of code starting from reset. These facilities are built using
JTAG JTAG (named after the Joint Test Action Group which codified it) is an industry standard for verifying designs and testing printed circuit boards after manufacture. JTAG implements standards for on-chip instrumentation in electronic design aut ...
support, though some newer cores optionally support ARM's own two-wire "SWD" protocol. In ARM7TDMI cores, the "D" represented JTAG debug support, and the "I" represented presence of an "EmbeddedICE" debug module. For ARM7 and ARM9 core generations, EmbeddedICE over JTAG was a de facto debug standard, though not architecturally guaranteed. The ARMv7 architecture defines basic debug facilities at an architectural level. These include breakpoints, watchpoints and instruction execution in a "Debug Mode"; similar facilities were also available with EmbeddedICE. Both "halt mode" and "monitor" mode debugging are supported. The actual transport mechanism used to access the debug facilities is not architecturally specified, but implementations generally include JTAG support. There is a separate ARM "CoreSight" debug architecture, which is not architecturally required by ARMv7 processors.


Debug Access Port

The Debug Access Port (DAP) is an implementation of an ARM Debug Interface. There are two different supported implementations, the Serial Wire
JTAG JTAG (named after the Joint Test Action Group which codified it) is an industry standard for verifying designs and testing printed circuit boards after manufacture. JTAG implements standards for on-chip instrumentation in electronic design aut ...
Debug Port (SWJ-DP) and the Serial Wire Debug Port (SW-DP). CMSIS-DAP is a standard interface that describes how various debugging software on a host PC can communicate over USB to firmware running on a hardware debugger, which in turn talks over SWD or JTAG to a CoreSight-enabled ARM Cortex CPU.


DSP enhancement instructions

To improve the ARM architecture for
digital signal processing Digital signal processing (DSP) is the use of digital processing, such as by computers or more specialized digital signal processors, to perform a wide variety of signal processing operations. The digital signals processed in this manner are ...
and multimedia applications, DSP instructions were added to the set. These are signified by an "E" in the name of the ARMv5TE and ARMv5TEJ architectures. E-variants also imply T, D, M, and I. The new instructions are common in
digital signal processor A digital signal processor (DSP) is a specialized microprocessor chip, with its architecture optimized for the operational needs of digital signal processing. DSPs are fabricated on MOS integrated circuit chips. They are widely used in audio s ...
(DSP) architectures. They include variations on signed multiply–accumulate, saturated add and subtract, and
count leading zeros In computer software and hardware, find first set (ffs) or find first one is a bit operation that, given an unsigned machine word, designates the index or position of the least significant bit set to one in the word counting from the least signi ...
.


SIMD extensions for multimedia

Introduced in the ARMv6 architecture, this was a precursor to Advanced SIMD, also named
Neon Neon is a chemical element with the symbol Ne and atomic number 10. It is a noble gas. Neon is a colorless, odorless, inert monatomic gas under standard conditions, with about two-thirds the density of air. It was discovered (along with krypt ...
.


Jazelle

Jazelle DBX (Direct Bytecode eXecution) is a technique that allows
Java bytecode In computing, Java bytecode is the bytecode-structured instruction set of the Java virtual machine (JVM), a virtual machine that enables a computer to run programs written in the Java programming language and several other programming langua ...
to be executed directly in the ARM architecture as a third execution state (and instruction set) alongside the existing ARM and Thumb-mode. Support for this state is signified by the "J" in the ARMv5TEJ architecture, and in ARM9EJ-S and ARM7EJ-S core names. Support for this state is required starting in ARMv6 (except for the ARMv7-M profile), though newer cores only include a trivial implementation that provides no hardware acceleration.


Thumb

To improve compiled code density, processors since the ARM7TDMI (released in 1994) have featured the ''Thumb'' instruction set, which have their own state. (The "T" in "TDMI" indicates the Thumb feature.) When in this state, the processor executes the Thumb instruction set, a compact 16-bit encoding for a subset of the ARM instruction set. Most of the Thumb instructions are directly mapped to normal ARM instructions. The space saving comes from making some of the instruction operands implicit and limiting the number of possibilities compared to the ARM instructions executed in the ARM instruction set state. In Thumb, the 16-bit opcodes have less functionality. For example, only branches can be conditional, and many opcodes are restricted to accessing only half of all of the CPU's general-purpose registers. The shorter opcodes give improved code density overall, even though some operations require extra instructions. In situations where the memory port or bus width is constrained to less than 32 bits, the shorter Thumb opcodes allow increased performance compared with 32-bit ARM code, as less program code may need to be loaded into the processor over the constrained memory bandwidth. Unlike processor architectures with variable length (16- or 32-bit) instructions, such as the Cray-1 and
Hitachi () is a Japanese multinational conglomerate corporation headquartered in Chiyoda, Tokyo, Japan. It is the parent company of the Hitachi Group (''Hitachi Gurūpu'') and had formed part of the Nissan ''zaibatsu'' and later DKB Group and Fuyo G ...
SuperH SuperH (or SH) is a 32-bit reduced instruction set computing (RISC) instruction set architecture (ISA) developed by Hitachi and currently produced by Renesas. It is implemented by microcontrollers and microprocessors for embedded systems. At the ...
, the ARM and Thumb instruction sets exist independently of each other. Embedded hardware, such as the
Game Boy Advance The (GBA) is a 32-bit handheld game console developed, manufactured and marketed by Nintendo as the successor to the Game Boy Color. It was released in Japan on March 21, 2001, in North America on June 11, 2001, in the PAL region on June 22, ...
, typically have a small amount of RAM accessible with a full 32-bit datapath; the majority is accessed via a 16-bit or narrower secondary datapath. In this situation, it usually makes sense to compile Thumb code and hand-optimise a few of the most CPU-intensive sections using full 32-bit ARM instructions, placing these wider instructions into the 32-bit bus accessible memory. The first processor with a Thumb
instruction decoder A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, a ...
was the ARM7TDMI. All ARM9 and later families, including XScale, have included a Thumb instruction decoder. It includes instructions adopted from the Hitachi
SuperH SuperH (or SH) is a 32-bit reduced instruction set computing (RISC) instruction set architecture (ISA) developed by Hitachi and currently produced by Renesas. It is implemented by microcontrollers and microprocessors for embedded systems. At the ...
(1992), which was licensed by ARM. ARM's smallest processor families (Cortex M0 and M1) implement only the 16-bit Thumb instruction set for maximum performance in lowest cost applications.


Thumb-2

''Thumb-2'' technology was introduced in the ''ARM1156 core'', announced in 2003. Thumb-2 extends the limited 16-bit instruction set of Thumb with additional 32-bit instructions to give the instruction set more breadth, thus producing a variable-length instruction set. A stated aim for Thumb-2 was to achieve code density similar to Thumb with performance similar to the ARM instruction set on 32-bit memory. Thumb-2 extends the Thumb instruction set with bit-field manipulation, table branches and conditional execution. At the same time, the ARM instruction set was extended to maintain equivalent functionality in both instruction sets. A new "Unified Assembly Language" (UAL) supports generation of either Thumb or ARM instructions from the same source code; versions of Thumb seen on ARMv7 processors are essentially as capable as ARM code (including the ability to write interrupt handlers). This requires a bit of care, and use of a new "IT" (if-then) instruction, which permits up to four successive instructions to execute based on a tested condition, or on its inverse. When compiling into ARM code, this is ignored, but when compiling into Thumb it generates an actual instruction. For example: ; if (r0

r1) CMP r0, r1 ITE EQ ; ARM: no code ... Thumb: IT instruction ; then r0 = r2; MOVEQ r0, r2 ; ARM: conditional; Thumb: condition via ITE 'T' (then) ; else r0 = r3; MOVNE r0, r3 ; ARM: conditional; Thumb: condition via ITE 'E' (else) ; recall that the Thumb MOV instruction has no bits to encode "EQ" or "NE".
All ARMv7 chips support the Thumb instruction set. All chips in the Cortex-A series, Cortex-R series, and ARM11 series support both "ARM instruction set state" and "Thumb instruction set state", while chips in the
Cortex-M The ARM Cortex-M is a group of 32-bit RISC ARM processor cores licensed by Arm Holdings. These cores are optimized for low-cost and energy-efficient integrated circuits, which have been embedded in tens of billions of consumer devices. Though ...
series support only the Thumb instruction set.


Thumb Execution Environment (ThumbEE)

''ThumbEE'' (erroneously called ''Thumb-2EE'' in some ARM documentation), which was marketed as Jazelle RCT (Runtime Compilation Target), was announced in 2005 and deprecated in 2011. It first appeared in the ''Cortex-A8'' processor. ThumbEE is a fourth instruction set state, making small changes to the Thumb-2 extended instruction set. These changes make the instruction set particularly suited to code generated at runtime (e.g. by JIT compilation) in managed ''Execution Environments''. ThumbEE is a target for languages such as
Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mo ...
, C#,
Perl Perl is a family of two high-level, general-purpose, interpreted, dynamic programming languages. "Perl" refers to Perl 5, but from 2000 to 2019 it also referred to its redesigned "sister language", Perl 6, before the latter's name was offic ...
, and Python, and allows JIT compilers to output smaller compiled code without reducing performance. New features provided by ThumbEE include automatic null pointer checks on every load and store instruction, an instruction to perform an array bounds check, and special instructions that call a handler. In addition, because it utilises Thumb-2 technology, ThumbEE provides access to registers r8–r15 (where the Jazelle/DBX Java VM state is held). Handlers are small sections of frequently called code, commonly used to implement high level languages, such as allocating memory for a new object. These changes come from repurposing a handful of opcodes, and knowing the core is in the new ThumbEE state. On 23 November 2011, Arm deprecated any use of the ThumbEE instruction set, and Armv8 removes support for ThumbEE.


Floating-point (VFP)

''VFP'' (Vector Floating Point) technology is a
floating-point unit In computing, floating-point arithmetic (FP) is arithmetic that represents real numbers approximately, using an integer with a fixed precision, called the significand, scaled by an integer exponent of a fixed base. For example, 12.345 can be ...
(FPU) coprocessor extension to the ARM architecture (implemented differently in Armv8 – coprocessors not defined there). It provides low-cost
single-precision Single-precision floating-point format (sometimes called FP32 or float32) is a computer number format, usually occupying 32 bits in computer memory; it represents a wide dynamic range of numeric values by using a floating radix point. A floatin ...
and
double-precision floating-point Double-precision floating-point format (sometimes called FP64 or float64) is a floating-point number format, usually occupying 64 bits in computer memory; it represents a wide dynamic range of numeric values by using a floating radix point. Flo ...
computation fully compliant with the '' ANSI/IEEE Std 754-1985 Standard for Binary Floating-Point Arithmetic''. VFP provides floating-point computation suitable for a wide spectrum of applications such as PDAs, smartphones, voice compression and decompression, three-dimensional graphics and digital audio, printers, set-top boxes, and automotive applications. The VFP architecture was intended to support execution of short "vector mode" instructions but these operated on each vector element sequentially and thus did not offer the performance of true
single instruction, multiple data Single instruction, multiple data (SIMD) is a type of parallel processing in Flynn's taxonomy. SIMD can be internal (part of the hardware design) and it can be directly accessible through an instruction set architecture (ISA), but it should ...
(SIMD) vector parallelism. This vector mode was therefore removed shortly after its introduction, to be replaced with the much more powerful Advanced SIMD, also named
Neon Neon is a chemical element with the symbol Ne and atomic number 10. It is a noble gas. Neon is a colorless, odorless, inert monatomic gas under standard conditions, with about two-thirds the density of air. It was discovered (along with krypt ...
. Some devices such as the ARM Cortex-A8 have a cut-down ''VFPLite'' module instead of a full VFP module, and require roughly ten times more clock cycles per float operation. Pre-Armv8 architecture implemented floating-point/SIMD with the coprocessor interface. Other floating-point and/or SIMD units found in ARM-based processors using the coprocessor interface include
FPA FPA may refer to: Broadcasting and entertainment * '' Fancy Pants Adventures'', an online game * Feminist Porn Award, a Canadian adult film award * First-person adventure, a video game genre * Fundação Padre Anchieta, a Brazilian educational ...
, FPE, iwMMXt, some of which were implemented in software by trapping but could have been implemented in hardware. They provide some of the same functionality as VFP but are not
opcode In computing, an opcode (abbreviated from operation code, also known as instruction machine code, instruction code, instruction syllable, instruction parcel or opstring) is the portion of a machine language instruction that specifies the operat ...
-compatible with it. FPA10 also provides
extended precision Extended precision refers to floating-point number formats that provide greater precision than the basic floating-point formats. Extended precision formats support a basic format by minimizing roundoff and overflow errors in intermediate value ...
, but implements correct rounding (required by IEEE 754) only in single precision. ; VFPv1: Obsolete ; VFPv2: An optional extension to the ARM instruction set in the ARMv5TE, ARMv5TEJ and ARMv6 architectures. VFPv2 has 16 64-bit FPU registers. ; VFPv3 or VFPv3-D32: Implemented on most Cortex-A8 and A9 ARMv7 processors. It is backward-compatible with VFPv2, except that it cannot trap floating-point exceptions. VFPv3 has 32 64-bit FPU registers as standard, adds VCVT instructions to convert between scalar, float and double, adds immediate mode to VMOV such that constants can be loaded into FPU registers. ; VFPv3-D16: As above, but with only 16 64-bit FPU registers. Implemented on Cortex-R4 and R5 processors and the Tegra 2 (Cortex-A9). ; VFPv3-F16: Uncommon; it supports IEEE754-2008 half-precision (16-bit) floating point as a storage format. ; VFPv4 or VFPv4-D32:Implemented on Cortex-A12 and A15 ARMv7 processors, Cortex-A7 optionally has VFPv4-D32 in the case of an FPU with Neon. VFPv4 has 32 64-bit FPU registers as standard, adds both half-precision support as a storage format and
fused multiply-accumulate Fuse or FUSE may refer to: Devices * Fuse (electrical), a device used in electrical systems to protect against excessive current ** Fuse (automotive), a class of fuses for vehicles * Fuse (hydraulic), a device used in hydraulic systems to protect ...
instructions to the features of VFPv3. ; VFPv4-D16: As above, but it has only 16 64-bit FPU registers. Implemented on Cortex-A5 and A7 processors in the case of an FPU without Neon. ; VFPv5-D16-M: Implemented on Cortex-M7 when single and double-precision floating-point core option exists. In
Debian Debian (), also known as Debian GNU/Linux, is a Linux distribution composed of free and open-source software, developed by the community-supported Debian Project, which was established by Ian Murdock on August 16, 1993. The first version of De ...
Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, whi ...
and derivatives such as
Ubuntu Ubuntu ( ) is a Linux distribution based on Debian and composed mostly of free and open-source software. Ubuntu is officially released in three editions: '' Desktop'', ''Server'', and ''Core'' for Internet of things devices and robots. All ...
and Linux Mint, armhf (ARM hard float) refers to the ARMv7 architecture including the additional VFP3-D16 floating-point hardware extension (and Thumb-2) above. Software packages and cross-compiler tools use the armhf vs. arm/armel suffixes to differentiate.


Advanced SIMD (Neon)

The ''Advanced SIMD'' extension (aka ''Neon'' or "MPE" Media Processing Engine) is a combined 64- and 128-bit SIMD instruction set that provides standardised acceleration for media and signal processing applications. Neon is included in all Cortex-A8 devices, but is optional in Cortex-A9 devices. Neon can execute MP3 audio decoding on CPUs running at 10 MHz, and can run the
GSM The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation ( 2G) digital cellular networks used by mobile devices such ...
adaptive multi-rate The Adaptive Multi-Rate (AMR, AMR-NB or GSM-AMR) audio codec is an audio compression format optimized for speech coding. AMR speech codec consists of a multi-rate narrowband speech codec that encodes narrowband (200–3400 Hz) signals at var ...
(AMR) speech codec at 13 MHz. It features a comprehensive instruction set, separate register files, and independent execution hardware. Neon supports 8-, 16-, 32-, and 64-bit integer and single-precision (32-bit) floating-point data and SIMD operations for handling audio and video processing as well as graphics and gaming processing. In Neon, the SIMD supports up to 16 operations at the same time. The Neon hardware shares the same floating-point registers as used in VFP. Devices such as the ARM Cortex-A8 and Cortex-A9 support 128-bit vectors, but will execute with 64 bits at a time, whereas newer Cortex-A15 devices can execute 128 bits at a time. A quirk of Neon in Armv7 devices is that it flushes all subnormal numbers to zero, and as a result the GCC compiler will not use it unless , which allows losing denormals, is turned on. "Enhanced" Neon defined since Armv8 does not have this quirk, but as of the same flag is still required to enable Neon instructions. On the other hand, GCC does consider Neon safe on AArch64 for Armv8. ProjectNe10 is ARM's first open-source project (from its inception; while they acquired an older project, now named Mbed TLS). The Ne10 library is a set of common, useful functions written in both Neon and C (for compatibility). The library was created to allow developers to use Neon optimisations without learning Neon, but it also serves as a set of highly optimised Neon intrinsic and assembly code examples for common DSP, arithmetic, and image processing routines. The source code is available on GitHub.


ARM Helium technology

Helium is the M-Profile Vector Extension (MVE). It adds more than 150 scalar and vector instructions.


Security extensions


TrustZone (for Cortex-A profile)

The Security Extensions, marketed as TrustZone Technology, is in ARMv6KZ and later application profile architectures. It provides a low-cost alternative to adding another dedicated security core to an SoC, by providing two virtual processors backed by hardware based access control. This lets the application core switch between two states, referred to as ''worlds'' (to reduce confusion with other names for capability domains), to prevent information leaking from the more trusted world to the less trusted world. This world switch is generally orthogonal to all other capabilities of the processor, thus each world can operate independently of the other while using the same core. Memory and peripherals are then made aware of the operating world of the core and may use this to provide access control to secrets and code on the device. Typically, a rich operating system is run in the less trusted world, with smaller security-specialised code in the more trusted world, aiming to reduce the attack surface. Typical applications include DRM functionality for controlling the use of media on ARM-based devices, and preventing any unapproved use of the device. In practice, since the specific implementation details of proprietary TrustZone implementations have not been publicly disclosed for review, it is unclear what level of assurance is provided for a given threat model, but they are not immune from attack. Open Virtualization is an open source implementation of the trusted world architecture for TrustZone. AMD has licensed and incorporated TrustZone technology into its Secure Processor Technology. Enabled in some but not all products, AMD's APUs include a Cortex-A5 processor for handling secure processing. In fact, the Cortex-A5 TrustZone core had been included in earlier AMD products, but was not enabled due to time constraints. Samsung Knox uses TrustZone for purposes such as detecting modifications to the kernel, storing certificates and attestating keys.


TrustZone for Armv8-M (for Cortex-M profile)

The Security Extension, marketed as TrustZone for Armv8-M Technology, was introduced in the Armv8-M architecture. While containing similar concepts to TrustZone for Armv8-A, it has a different architectural design, as world switching is performed using branch instructions instead of using exceptions. It also supports safe interleaved interrupt handling from either world regardless of the current security state. Together these features provide low latency calls to the secure world and responsive interrupt handling. ARM provides a reference stack of secure world code in the form of Trusted Firmware for M and
PSA Certified Platform Security Architecture (PSA) Certified is a security certification scheme for Internet of Things (IoT) hardware, software and devices. It was created by Arm Holdings, Brightsight, CAICT, Prove & Run, Riscure, TrustCB and UL as part of ...
.


No-execute page protection

As of ARMv6, the ARM architecture supports no-execute page protection, which is referred to as ''XN'', for ''eXecute Never''.


Large Physical Address Extension (LPAE)

The Large Physical Address Extension (LPAE), which extends the physical address size from 32 bits to 40 bits, was added to the Armv7-A architecture in 2011. The physical address size may be even larger in processors based on the 64-bit (Armv8-A) architecture. For example, it is 44 bits in Cortex-A75 and Cortex-A65AE.


Armv8-R and Armv8-M

The Armv8-R and Armv8-M architectures, announced after the Armv8-A architecture, share some features with Armv8-A. However, Armv8-M does not include any 64-bit AArch64 instructions, and Armv8-R originally did not include any AArch64 instructions; those instructions were added to Armv8-R later.


Armv8.1-M

The Armv8.1-M architecture, announced in February 2019, is an enhancement of the Armv8-M architecture. It brings new features including: * A new vector instruction set extension. The M-Profile Vector Extension (MVE), or Helium, is for signal processing and machine learning applications. * Additional instruction set enhancements for loops and branches (Low Overhead Branch Extension). * Instructions for half-precision floating-point support. * Instruction set enhancement for TrustZone management for Floating Point Unit (FPU). * New memory attribute in the Memory Protection Unit (MPU). * Enhancements in debug including Performance Monitoring Unit (PMU), Unprivileged Debug Extension, and additional debug support focus on signal processing application developments. * Reliability, Availability and Serviceability (RAS) extension.


64/32-bit architecture


Armv8


Armv8-A

Announced in October 2011, Armv8-A (often called ARMv8 while the Armv8-R is also available) represents a fundamental change to the ARM architecture. It adds an optional 64-bit architecture named "AArch64" and the associated new "A64" instruction set. AArch64 provides
user-space A modern computer operating system usually segregates virtual memory into user space and kernel space. Primarily, this separation serves to provide memory protection and hardware protection from malicious or errant software behaviour. Kerne ...
compatibility with Armv7-A, the 32-bit architecture, therein referred to as "AArch32" and the old 32-bit instruction set, now named "A32". The Thumb instruction set is referred to as "T32" and has no 64-bit counterpart. Armv8-A allows 32-bit applications to be executed in a 64-bit OS, and a 32-bit OS to be under the control of a 64-bit
hypervisor A hypervisor (also known as a virtual machine monitor, VMM, or virtualizer) is a type of computer software, firmware or hardware that creates and runs virtual machines. A computer on which a hypervisor runs one or more virtual machines is called ...
. ARM announced their Cortex-A53 and Cortex-A57 cores on 30 October 2012. Apple was the first to release an Armv8-A compatible core in a consumer product ( Apple A7 in
iPhone 5S The iPhone 5S (stylized and marketed as iPhone 5s) is a smartphone that was designed and marketed by Apple Inc. It is the seventh generation of the iPhone, succeeding the iPhone 5, and unveiled in September 2013, alongside the iPhone 5C. ...
).
AppliedMicro Applied Micro Circuits Corporation (also known as AppliedMicro, AMCC or APM) was a fabless semiconductor company designing network and embedded Power ISA (including a Power ISA license), and server processor ARM (including an ARMv8-A license), ...
, using an
FPGA A field-programmable gate array (FPGA) is an integrated circuit designed to be configured by a customer or a designer after manufacturinghence the term '' field-programmable''. The FPGA configuration is generally specified using a hardware d ...
, was the first to demo Armv8-A. The first Armv8-A SoC from
Samsung The Samsung Group (or simply Samsung) ( ko, 삼성 ) is a South Korean multinational manufacturing conglomerate headquartered in Samsung Town, Seoul, South Korea. It comprises numerous affiliated businesses, most of them united under the ...
is the Exynos 5433 used in the
Galaxy Note 4 The Samsung Galaxy Note 4 is an Android smartphone developed and produced by Samsung Electronics. It was unveiled during a Samsung press conference at IFA Berlin on 3 September 2014 and was released globally in October 2014 as successor to th ...
, which features two clusters of four Cortex-A57 and Cortex-A53 cores in a big.LITTLE configuration; but it will run only in AArch32 mode. To both AArch32 and AArch64, Armv8-A makes VFPv3/v4 and advanced SIMD (Neon) standard. It also adds cryptography instructions supporting AES,
SHA-1 In cryptography, SHA-1 (Secure Hash Algorithm 1) is a cryptographically broken but still widely used hash function which takes an input and produces a 160- bit (20- byte) hash value known as a message digest – typically rendered as 40 hexa ...
/ SHA-256 and
finite field arithmetic In mathematics, finite field arithmetic is arithmetic in a finite field (a field containing a finite number of elements) contrary to arithmetic in a field with an infinite number of elements, like the field of rational numbers. There are infini ...
. AArch64 was introduced in Armv8-A and its subsequent revision. AArch64 is not included in the 32-bit Armv8-R and Armv8-M architectures.


Armv8-R

Optional AArch64 support was added to the Armv8-R profile, with the first ARM core implementing it being the Cortex-R82. It adds the A64 instruction set.


Armv9


Armv9-A

Announced in March 2021, the updated architecture places a focus on secure execution and compartmentalisation.


Arm SystemReady

Arm SystemReady
formerly named Arm ServerReady, is a certification program that helps land the generic off-the-shelf operating systems and hypervisors on to the Arm-based systems from datacenter servers to industrial edge and IoT devices. The key building blocks of the program are the specifications for minimum hardware and firmware requirements that the operating systems and hypervisors can rely upon. These specifications are:
Base System Architecture (BSA)
and the market segment specific supplements (e.g.
Server BSA supplement

Base Boot Requirements (BBR)
an
Base Boot Security Requirements (BBR)
These specifications are co-developed by Arm and its partners in the System Architecture Advisory Committee (SystemArchAC). Architecture Compliance Suite (ACS) is the test tools that help to check the compliance of these specifications. Th
Arm SystemReady Requirements Specification
documents the requirements of the certifications. This program was introduced by Arm in 2020 at the first DevSummit event. Its predecessor Arm ServerReady was introduced in 2018 at the Arm TechCon event. This program currently includes four bands: * SystemReady SR: this band is for servers that support operating systems and hypervisors that expect
UEFI UEFI (Unified Extensible Firmware Interface) is a set of specifications written by the UEFI Forum. They define the architecture of the platform firmware used for booting and its interface for interaction with the operating system. Examples ...
,
ACPI Advanced Configuration and Power Interface (ACPI) is an open standard that operating systems can use to discover and configure computer hardware components, to perform power management (e.g. putting unused hardware components to sleep), auto con ...
and
SMBIOS In computing, the System Management BIOS (SMBIOS) specification defines data structures (and access methods) that can be used to read management information produced by the BIOS of a computer. This eliminates the need for the operating system to ...
interfaces. * SystemReady LS: this band is for servers that hyperscalers use to support Linux operating systems that expect
LinuxBoot LinuxBoot is a free software project aimed at replacing most of the Driver Execution Environment (DXE) modules in Unified Extensible Firmware Interface (UEFI) firmware with the Linux kernel. LinuxBoot must run on top of hardware initialisation so ...
firmware along with the ACPI and SMBIOS interfaces. * SystemReady ES: this band is for the industrial edge and IoT devices that support operating systems and hypervisors that expect UEFI, ACPI and SMBIOS interfaces. * SystemReady IR: this band is for the industrial edge and IoT devices that support operating systems that expect UEFI and devicetree interfaces.


PSA Certified

PSA Certified Platform Security Architecture (PSA) Certified is a security certification scheme for Internet of Things (IoT) hardware, software and devices. It was created by Arm Holdings, Brightsight, CAICT, Prove & Run, Riscure, TrustCB and UL as part of ...
, formerly named Platform Security Architecture, is an architecture-agnostic security framework and evaluation scheme. It is intended to help secure
Internet of Things The Internet of things (IoT) describes physical objects (or groups of such objects) with sensors, processing ability, software and other technologies that connect and exchange data with other devices and systems over the Internet or other com ...
(IoT) devices built on system-on-a-chip (SoC) processors. It was introduced to increase security where a full trusted execution environment is too large or complex. The architecture was introduced by Arm in 2017 at the annual TechCon event. Although the scheme is architecture agnostic, it was first implemented on Arm Cortex-M processor cores intended for microcontroller use. PSA Certified includes freely available threat models and security analyses that demonstrate the process for deciding on security features in common IoT products. It also provides freely downloadable application programming interface (API) packages, architectural specifications, open-source firmware implementations, and related test suites. Following the development of the architecture security framework in 2017, the
PSA Certified Platform Security Architecture (PSA) Certified is a security certification scheme for Internet of Things (IoT) hardware, software and devices. It was created by Arm Holdings, Brightsight, CAICT, Prove & Run, Riscure, TrustCB and UL as part of ...
assurance scheme launched two years later at Embedded World in 2019. PSA Certified offers a multi-level security evaluation scheme for chip vendors, OS providers and IoT device makers. The Embedded World presentation introduced chip vendors to Level 1 Certification. A draft of Level 2 protection was presented at the same time. Level 2 certification became a usable standard in February 2020. The certification was created by PSA Joint Stakeholders to enable a security-by-design approach for a diverse set of IoT products. PSA Certified specifications are implementation and architecture agnostic, as a result they can be applied to any chip, software or device. The certification also removes industry fragmentation for IoT product manufacturers and developers.


Operating system support


32-bit operating systems


Historical operating systems

The first 32-bit ARM-based personal computer, the
Acorn Archimedes Acorn Archimedes is a family of personal computers designed by Acorn Computers of Cambridge, England. The systems are based on Acorn's own ARM architecture processors and the proprietary operating systems Arthur and RISC OS. The first mode ...
, was originally intended to run an ambitious operating system called
ARX Arx, ARX, or ArX may refer to: * ARX (Algorithmic Research Ltd.), a digital security company *ARX (gene), Aristaless related homeobox *ARX (operating system), an operating system * ArX (revision control), revision control software *Arx (Roman), a ...
. The machines shipped with RISC OS which was also used on later ARM-based systems from Acorn and other vendors. Some early Acorn machines were also able to run a
Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, ...
port called RISC iX. (Neither is to be confused with RISC/os, a contemporary Unix variant for the MIPS architecture.)


Embedded operating systems

The 32-bit ARM architecture is supported by a large number of embedded and real-time operating systems, including: * A2 * Android * ChibiOS/RT * Deos *
DRYOS DRYOS is a real-time operating system made by Canon and is used in their latest digital cameras and camcorders. Since late 2007 DIGIC-based cameras are shipped using DryOS. It replaces VxWorks from Wind River Systems which has been used before on ...
* eCos * embOS *
FreeBSD FreeBSD is a free and open-source Unix-like operating system descended from the Berkeley Software Distribution (BSD), which was based on Research Unix. The first version of FreeBSD was released in 1993. In 2005, FreeBSD was the most popular ...
*
FreeRTOS FreeRTOS is a real-time operating system kernel for embedded devices that has been ported to 35 microcontroller platforms. It is distributed under the MIT License. History The FreeRTOS kernel was originally developed by Richard Barry around ...
*
INTEGRITY Integrity is the practice of being honest and showing a consistent and uncompromising adherence to strong moral and ethical principles and values. In ethics, integrity is regarded as the honesty and truthfulness or accuracy of one's actions. In ...
*
Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, whi ...
* Micro-Controller Operating Systems *
Mbed Mbed is a platform and operating system for internet-connected devices based on 32-bit ARM Cortex-M microcontrollers. Such devices are also known as Internet of Things devices. The project is collaboratively developed by Arm and its technology p ...
*
MINIX 3 Minix 3 is a small, Unix-like operating system. It is published under a BSD-3-Clause license and is a successor project to the earlier versions, Minix 1 and 2. The project's main goal is for the system to be fault-tolerant by detecting and ...
*
MQX MQX (Message Queue eXecutive) is a real-time operating system (RTOS) developed by Precise Software Technologies, Inc., and currently sold by Synopsys, Embedded Access, Inc., and NXP Semiconductors. Like most RTOSs, MQX includes a multitasking k ...
* Nucleus PLUS *
NuttX NuttX is a free and open-source Real-Time Operating System (RTOS) with an emphasis on technical standards compliance and on having a small footprint. Scalable from 8-bit to 64-bit microcontroller environments, the main governing standards in Nut ...
*
Operating System Embedded Enea AB is a global information technology company with its headquarters in Kista, Sweden that provides real-time operating systems and consulting services. Enea, which is an abbreviation of ''Engmans Elektronik Aktiebolag'', also produces the OS ...
(OSE) * OS-9 * Pharos * Plan 9 *
PikeOS PikeOS is a commercial, hard real-time operating system (RTOS) that offers a separation kernel based hypervisor with multiple logical partition types for many other operating systems (OS), each called a GuestOS, and applications. It enables use ...
* QNX *
RIOT A riot is a form of civil disorder commonly characterized by a group lashing out in a violent public disturbance against authority, property, or people. Riots typically involve destruction of property, public or private. The property targete ...
* RTEMS *
RTXC Quadros RTXC Quadros is a real time operating system (RTOS) written mainly in the C programming language. It is mainly intended for use in embedded system An embedded system is a computer system—a combination of a computer processor, computer ...
* SCIOPTA * ThreadX * TizenRT *
T-Kernel T-Kernel is an open source real-time operating system (RTOS) designed for 32-bit microcontrollers. It is standardized by the T-Engine Forum, which distributes it under a '' T-License'' agreement. There is also a corresponding Micro T-Kernel (μT- ...
*
VxWorks VxWorks is a real-time operating system (or RTOS) developed as proprietary software by Wind River Systems, a wholly-owned subsidiary of Aptiv. First released in 1987, VxWorks is designed for use in embedded systems requiring real-time, determi ...
* Windows Embedded Compact * Windows 10 IoT Core * Zephyr


Mobile device operating systems

The 32-bit ARM architecture is the primary hardware environment for most mobile device operating systems such as: * Android * BlackBerry OS/
BlackBerry 10 BlackBerry 10 is a discontinued proprietary mobile operating system for the BlackBerry line of smartphones, both developed by BlackBerry Limited (formerly Research In Motion). BlackBerry 10 is based on QNX, a Unix-like operating system that was ...
*
ChromeOS ChromeOS, sometimes stylized as chromeOS and formerly styled as Chrome OS, is a Linux-based operating system designed by Google. It is derived from the open-source ChromiumOS and uses the Google Chrome web browser as its principal user interfa ...
* Mobian * Sailfish *
postmarketOS postmarketOS (abbreviated as pmOS) is an operating system primarily for smartphones, based on the Alpine Linux distribution. postmarketOS was launched on 26 May 2017 with the source code available on GitHub before migrating to GitLab in 2018. I ...
*
Tizen Tizen () is a Linux-based mobile operating system backed by the Linux Foundation, mainly developed and used primarily by Samsung Electronics. The project was originally conceived as an HTML5-based platform for mobile devices to succeed MeeGo. ...
* Ubuntu Touch *
webOS webOS, also known as LG webOS and previously known as Open webOS, HP webOS and Palm webOS, is a Linux kernel-based multitasking operating system for smart devices such as smart TVs that has also been used as a mobile operating system. Initially ...
Formerly, but now discontinued: *
Bada Bada (stylized as bada; Korean: ) is a discontinued mobile operating system developed by Samsung Electronics for devices such as mid- to high-end smartphones and tablet computers. The name is derived from " (bada)", meaning "ocean" or "sea" in ...
* Firefox OS * MeeGo * Newton OS * iOS 10 and earlier *
Symbian Symbian is a discontinued mobile operating system (OS) and computing platform designed for smartphones. It was originally developed as a proprietary software OS for personal digital assistants in 1998 by the Symbian Ltd. consortium. Symbian OS ...
*
Windows 10 Mobile Windows 10 Mobile is a discontinued mobile operating system developed by Microsoft. First released in 2015, it is a successor to Windows Phone 8.1, but was marketed by Microsoft as being an edition of its PC operating system Windows 10. Wind ...
*
Windows RT Windows RT is a mobile operating system developed by Microsoft. It is a version of Windows 8 or Windows 8.1 built for the 32-bit ARM architecture (ARMv7). First unveiled in January 2011 at Consumer Electronics Show, the Windows RT 8 operat ...
*
Windows Phone Windows Phone (WP) is a discontinued family of mobile operating systems developed by Microsoft for smartphones as the replacement successor to Windows Mobile and Zune. Windows Phone featured a new user interface derived from the Metro design lan ...
*
Windows Mobile Windows Mobile is a discontinued family of mobile operating systems developed by Microsoft for smartphones and personal digital assistants. Its origin dated back to Windows CE in 1996, though Windows Mobile itself first appeared in 2000 as Pock ...


Desktop and server operating systems

The 32-bit ARM architecture is supported by RISC OS and by multiple
Unix-like A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-li ...
operating systems including: *
FreeBSD FreeBSD is a free and open-source Unix-like operating system descended from the Berkeley Software Distribution (BSD), which was based on Research Unix. The first version of FreeBSD was released in 1993. In 2005, FreeBSD was the most popular ...
*
NetBSD NetBSD is a free and open-source Unix operating system based on the Berkeley Software Distribution (BSD). It was the first open-source BSD descendant officially released after 386BSD was forked. It continues to be actively developed and is ava ...
*
OpenBSD OpenBSD is a security-focused, free and open-source, Unix-like operating system based on the Berkeley Software Distribution (BSD). Theo de Raadt created OpenBSD in 1995 by forking NetBSD 1.0. According to the website, the OpenBSD project e ...
*
OpenSolaris OpenSolaris () is a discontinued open-source computer operating system based on Solaris and created by Sun Microsystems. It was also, perhaps confusingly, the name of a project initiated by Sun to build a developer and user community around t ...
* several
Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, whi ...
distributions, such as: **
Debian Debian (), also known as Debian GNU/Linux, is a Linux distribution composed of free and open-source software, developed by the community-supported Debian Project, which was established by Ian Murdock on August 16, 1993. The first version of De ...
** Armbian ** Gentoo **
Ubuntu Ubuntu ( ) is a Linux distribution based on Debian and composed mostly of free and open-source software. Ubuntu is officially released in three editions: '' Desktop'', ''Server'', and ''Core'' for Internet of things devices and robots. All ...
** Raspberry Pi OS (formerly Raspbian) ** Slackware


64-bit operating systems


Embedded operating systems

*
INTEGRITY Integrity is the practice of being honest and showing a consistent and uncompromising adherence to strong moral and ethical principles and values. In ethics, integrity is regarded as the honesty and truthfulness or accuracy of one's actions. In ...
* OSE * SCIOPTA *
seL4 L4 is a family of second-generation microkernels, used to implement a variety of types of operating systems (OS), though mostly for Unix-like, ''Portable Operating System Interface'' (POSIX) compliant types. L4, like its predecessor microkernel ...
* Pharos *
FreeRTOS FreeRTOS is a real-time operating system kernel for embedded devices that has been ported to 35 microcontroller platforms. It is distributed under the MIT License. History The FreeRTOS kernel was originally developed by Richard Barry around ...
* QNX * Zephyr


Mobile device operating systems

* Android supports Armv8-A in
Android Lollipop Android Lollipop ( codenamed Android L during development) is the fifth major version of the Android mobile operating system developed by Google and the 12th version of Android, spanning versions between 5.0 and 5.1.1. Unveiled on June 25, 2014 ...
(5.0) and later. * iOS supports Armv8-A in
iOS 7 iOS 7 is the seventh major release of the iOS mobile operating system developed by Apple Inc., being the successor to iOS 6. It was announced at the company's Worldwide Developers Conference on June 10, 2013, and was released on September 1 ...
and later on 64-bit Apple SoCs.
iOS 11 iOS 11 is the iOS version history, eleventh major release of the iOS mobile operating system developed by Apple Inc., being the successor to iOS 10. It was announced at the company's Apple Worldwide Developers Conference, Worldwide Developers C ...
and later only supports 64-bit ARM processors and applications. * Mobian *
PostmarketOS postmarketOS (abbreviated as pmOS) is an operating system primarily for smartphones, based on the Alpine Linux distribution. postmarketOS was launched on 26 May 2017 with the source code available on GitHub before migrating to GitLab in 2018. I ...
* Arch Linux ARM * Manjaro


Desktop and server operating systems

* Support for Armv8-A was merged into the
Linux kernel The Linux kernel is a free and open-source, monolithic, modular, multitasking, Unix-like operating system kernel. It was originally authored in 1991 by Linus Torvalds for his i386-based PC, and it was soon adopted as the kernel for the GNU ...
version 3.7 in late 2012. Armv8-A is supported by a number of
Linux distribution A Linux distribution (often abbreviated as distro) is an operating system made from a software collection that includes the Linux kernel and, often, a package management system. Linux users usually obtain their operating system by downloading one ...
s, such as: **
Debian Debian (), also known as Debian GNU/Linux, is a Linux distribution composed of free and open-source software, developed by the community-supported Debian Project, which was established by Ian Murdock on August 16, 1993. The first version of De ...
** Armbian ** Alpine Linux **
Ubuntu Ubuntu ( ) is a Linux distribution based on Debian and composed mostly of free and open-source software. Ubuntu is officially released in three editions: '' Desktop'', ''Server'', and ''Core'' for Internet of things devices and robots. All ...
**
Fedora A fedora () is a hat with a soft brim and indented crown.Kilgour, Ruth Edwards (1958). ''A Pageant of Hats Ancient and Modern''. R. M. McBride Company. It is typically creased lengthwise down the crown and "pinched" near the front on both side ...
**
openSUSE openSUSE () is a free and open source RPM-based Linux distribution developed by the openSUSE project. The initial release of the community project was a beta version of SUSE Linux 10.0. Additionally the project creates a variety of tools, s ...
**
SUSE Linux Enterprise SUSE Linux Enterprise (often abbreviated to SLE) is a Linux-based operating system developed by SUSE. It is available in two editions, suffixed with Server (SLES) for servers and mainframes, and Desktop (SLED) for workstations and desktop compute ...
**
RHEL Red Hat Enterprise Linux (RHEL) is a commercial open-source Linux distribution developed by Red Hat for the commercial market. Red Hat Enterprise Linux is released in server versions for x86-64, Power ISA, ARM64, and IBM Z and a desktop versio ...
** Raspberry Pi OS (formerly Raspbian. Beta version as of early 2022) * Support for Armv8-A was merged into
FreeBSD FreeBSD is a free and open-source Unix-like operating system descended from the Berkeley Software Distribution (BSD), which was based on Research Unix. The first version of FreeBSD was released in 1993. In 2005, FreeBSD was the most popular ...
in late 2014. *
OpenBSD OpenBSD is a security-focused, free and open-source, Unix-like operating system based on the Berkeley Software Distribution (BSD). Theo de Raadt created OpenBSD in 1995 by forking NetBSD 1.0. According to the website, the OpenBSD project e ...
has Armv8 support as of 2017. *
NetBSD NetBSD is a free and open-source Unix operating system based on the Berkeley Software Distribution (BSD). It was the first open-source BSD descendant officially released after 386BSD was forked. It continues to be actively developed and is ava ...
has Armv8 support as of early 2018. *
Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for se ...
-
Windows 10 Windows 10 is a major release of Microsoft's Windows NT operating system. It is the direct successor to Windows 8.1, which was released nearly two years earlier. It was released to manufacturing on July 15, 2015, and later to retail on ...
runs 32-bit " x86 and 32-bit ARM applications", as well as native ARM64 desktop apps;
Windows 11 Windows 11 is the latest major release of Microsoft's Windows NT operating system, released in October 2021. It is a free upgrade to its predecessor, Windows 10 (2015), and is available for any Windows 10 devices that meet the new Windows 11 ...
does so as well. Support for 64-bit ARM apps in the Microsoft Store has been available since November 2018. *
macOS macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and la ...
has ARM support starting with
macOS Big Sur macOS Big Sur (version 11) is the seventeenth major release of macOS, Apple Inc.'s operating system for Macintosh computers. It was announced at Apple's Worldwide Developers Conference (WWDC) on June 22, 2020, and was released to the publi ...
as of late 2020. Rosetta 2 adds support for
x86-64 x86-64 (also known as x64, x86_64, AMD64, and Intel 64) is a 64-bit version of the x86 instruction set, first released in 1999. It introduced two new modes of operation, 64-bit mode and compatibility mode, along with a new 4-level paging ...
applications but not virtualization of x86-64 computer platforms.


Porting to 32- or 64-bit ARM operating systems

Windows applications recompiled for ARM and linked with Winelib, from the
Wine Wine is an alcoholic drink typically made from Fermentation in winemaking, fermented grapes. Yeast in winemaking, Yeast consumes the sugar in the grapes and converts it to ethanol and carbon dioxide, releasing heat in the process. Different ...
project, can run on 32-bit or 64-bit ARM in Linux, FreeBSD, or other compatible operating systems. x86 binaries, e.g. when not specially compiled for ARM, have been demonstrated on ARM using
QEMU QEMU is a free and open-source emulator (Quick EMUlator). It emulates the machine's central processing unit, processor through dynamic binary translation and provides a set of different hardware and device models for the machine, enabling it t ...
with Wine (on Linux and more), but do not work at full speed or same capability as with Winelib.


Notes


See also

* Amber (processor) – an open-source ARM-compatible processor core * AMULET microprocessor – an asynchronous implementation of the ARM architecture *
Apple silicon Apple silicon is a series of system on a chip (SoC) and system in a package (SiP) processors designed by Apple Inc., mainly using the ARM architecture. It is the basis of most new Mac computers as well as iPhone, iPad, iPod Touch, Apple TV, ...
*
ARM Accredited Engineer ARM Accredited Engineer (AAE) was a program of professional accreditations awarded by ARM Holdings. The AAE program was designed for computer software and hardware engineers wishing to validate their knowledge of ARM technology. The program was ...
– certification program *
ARM big.LITTLE ARM big.LITTLE is a heterogeneous computing architecture developed by ARM Holdings, coupling relatively battery-saving and slower processor cores (''LITTLE'') with relatively more powerful and power-hungry ones (''big''). Typically, only one "s ...
– ARM's heterogeneous computing architecture ** DynamIQ *
ARMulator ARM Instruction Set Simulator, also known as ARMulator, is one of the software development tools provided by the development systems business unit of ARM Limited to all users of ARM-based chips. It owes its heritage to the early development of the ...
– an instruction set simulator *
Comparison of Armv7-A processors This is a comparison of processors based on the ARM family of instruction sets designed by ARM Holdings and 3rd parties, sorted by version of the ARM instruction set, release and name. ARMv6 ARMv7-A This is a table comparing central proc ...
* Comparison of Armv8-A processors * Meltdown (security vulnerability) *
RISC In computer engineering, a reduced instruction set computer (RISC) is a computer designed to simplify the individual instructions given to the computer to accomplish tasks. Compared to the instructions given to a complex instruction set comp ...
*
RISC-V RISC-V (pronounced "risk-five" where five refers to the number of generations of RISC architecture that were developed at the University of California, Berkeley since 1981) is an open standard instruction set architecture (ISA) based on est ...
* Spectre (security vulnerability) *
Unicore UNICORE (UNiform Interface to COmputing REsources) is a grid computing technology for resources such as supercomputers or cluster systems and information stored in databases. UNICORE was developed in two projects funded by the German ministry ...
– a 32-register architecture based heavily on a 32-bit ARM


References


Citations


Bibliography

*


Further reading


External links

* , ARM Ltd.


Architecture manuals

* - covers ARMv4, ARMv4T, ARMv5T, (ARMv5TExP), ARMv5TE, ARMv5TEJ, and ARMv6 * * * * * * * *
ARM Virtualization Extensions


Quick-reference cards


Instructions


Thumb

ARM and Thumb-2

Vector Floating Point


Opcodes


Thumb

ARM

GNU Assembler Directives
{{Authority control Acorn Computers Articles with example code Computer-related introductions in 1983 Instruction set architectures