HOME

TheInfoList



OR:

In computer architecture, 64-bit integers, memory addresses, or other
data In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpret ...
units are those that are 64 bits wide. Also, 64-bit CPUs and ALUs are those that are based on
processor register A processor register is a quickly accessible location available to a computer's processor. Registers usually consist of a small amount of fast storage, although some registers have specific hardware functions, and may be read-only or write-only. ...
s,
address 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 e ...
es, or data buses of that size. A
computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations ( computation) automatically. Modern digital electronic computers can perform generic sets of operations known as programs. These prog ...
that uses such a processor is a 64-bit computer. From the software perspective, 64-bit computing means the use of machine code with 64-bit
virtual memory In computing, virtual memory, or virtual storage is a memory management technique that provides an "idealized abstraction of the storage resources that are actually available on a given machine" which "creates the illusion to users of a very ...
addresses. However, not all 64-bit instruction sets support full 64-bit virtual memory addresses; x86-64 and ARMv8, for example, support only 48 bits of virtual address, with the remaining 16 bits of the virtual address required to be all 0's or all 1's, and several 64-bit instruction sets support fewer than 64 bits of physical memory address. The term ''64-bit'' also describes a generation of computers in which 64-bit processors are the norm. 64 bits is a
word A word is a basic element of language that carries an objective or practical meaning, can be used on its own, and is uninterruptible. Despite the fact that language speakers often have an intuitive grasp of what a word is, there is no conse ...
size that defines certain classes of computer architecture, buses, memory, and CPUs and, by extension, the software that runs on them. 64-bit CPUs have been used in
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 ...
s since the 1970s (
Cray-1 The Cray-1 was a supercomputer designed, manufactured and marketed by Cray Research. Announced in 1975, the first Cray-1 system was installed at Los Alamos National Laboratory in 1976. Eventually, over 100 Cray-1s were sold, making it one of the ...
, 1975) and in
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 ...
s (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 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 since the early 1990s. In 2003, 64-bit CPUs were introduced to the mainstream PC market in the form of x86-64 processors and the PowerPC G5. A 64-bit register can hold any of 264 (over 18 quintillion or 1.8×1019) different values. The range of
integer An integer is the number zero (), a positive natural number (, , , etc.) or a negative integer with a minus sign ( −1, −2, −3, etc.). The negative numbers are the additive inverses of the corresponding positive numbers. In the languag ...
values that can be stored in 64 bits depends on the integer representation used. With the two most common representations, the range is 0 through 18,446,744,073,709,551,615 (264 − 1) for representation as an ( unsigned)
binary number A binary number is a number expressed in the base-2 numeral system or binary numeral system, a method of mathematical expression which uses only two symbols: typically "0" ( zero) and "1" (one). The base-2 numeral system is a positional notati ...
, and −9223372036854775808 (−263) through 9223372036854775807 (263 − 1) for representation as two's complement. Hence, a processor with 64-bit memory addresses can directly access 264 bytes (16 exbibytes or EiB) of byte-addressable memory. With no further qualification, a ''64-bit computer architecture'' generally has integer and addressing registers that are 64 bits wide, allowing direct support for 64-bit data types and addresses. However, a CPU might have external data buses or
address 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 e ...
es with different sizes from the registers, even larger (the 32-bit Pentium had a 64-bit data bus, for instance).


Architectural implications

Processor registers are typically divided into several groups: ''integer'', ''floating-point'', ''
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), ''control'', and often special registers for address arithmetic which may have various uses and names such as ''address'', ''index'', or ''base registers''. However, in modern designs, these functions are often performed by more general purpose ''integer'' registers. In most processors, only integer or address-registers can be used to address data in memory; the other types of registers cannot. The size of these registers therefore normally limits the amount of directly addressable memory, even if there are registers, such as floating-point registers, that are wider. Most high performance 32-bit and 64-bit processors (some notable exceptions are older or embedded
ARM architecture 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 (RISC) instruction set architectures for computer processors, configured ...
(ARM) and 32-bit MIPS architecture (MIPS) CPUs) have integrated floating point hardware, which is often, but not always, based on 64-bit units of data. For example, although the x86/ x87 architecture has instructions able to load and store 64-bit (and 32-bit) floating-point values in memory, the internal floating point data and register format is 80 bits wide, while the general-purpose registers are 32 bits wide. In contrast, the 64-bit
Alpha Alpha (uppercase , lowercase ; grc, ἄλφα, ''álpha'', or ell, άλφα, álfa) is the first letter of the Greek alphabet. In the system of Greek numerals, it has a value of one. Alpha is derived from the Phoenician letter aleph , whi ...
family uses a 64-bit floating-point data and register format, and 64-bit integer registers.


History

Many computer instruction sets are designed so that a single integer register can store the memory address to any location in the computer's physical or
virtual memory In computing, virtual memory, or virtual storage is a memory management technique that provides an "idealized abstraction of the storage resources that are actually available on a given machine" which "creates the illusion to users of a very ...
. Therefore, the total number of addresses to memory is often determined by the width of these registers. The IBM System/360 of the 1960s was an early 32-bit computer; it had 32-bit integer registers, although it only used the low order 24 bits of a word for addresses, resulting in a 16 
MiB The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable unit ...
() address space. 32-bit superminicomputers, such as the DEC VAX, became common in the 1970s, and 32-bit microprocessors, such as the Motorola 68000 family and the 32-bit members of the x86 family starting with the Intel 80386, appeared in the mid-1980s, making 32 bits something of a ''de facto'' consensus as a convenient register size. A 32-bit address register meant that 232 addresses, or 4  GiB of
random-access memory Random-access memory (RAM; ) is a form of computer memory that can be read and changed in any order, typically used to store working data and machine code. A random-access memory device allows data items to be read or written in almost the ...
(RAM), could be referenced. When these architectures were devised, 4 GiB of memory was so far beyond the typical amounts (4 MiB) in installations, that this was considered to be enough ''headroom'' for addressing. 4.29 billion addresses were considered an appropriate size to work with for another important reason: 4.29 billion integers are enough to assign unique references to most entities in applications like
database In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases ...
s. Some
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 ...
architectures of the 1970s and 1980s, such as the
Cray-1 The Cray-1 was a supercomputer designed, manufactured and marketed by Cray Research. Announced in 1975, the first Cray-1 system was installed at Los Alamos National Laboratory in 1976. Eventually, over 100 Cray-1s were sold, making it one of the ...
, used registers up to 64 bits wide, and supported 64-bit integer arithmetic, although they did not support 64-bit addressing. In the mid-1980s, Intel i860 development began culminating in a (too late for Windows NT) 1989 release; the i860 had 32-bit integer registers and 32-bit addressing, so it was not a fully 64-bit processor, although its graphics unit supported 64-bit integer arithmetic. However, 32 bits remained the norm until the early 1990s, when the continual reductions in the cost of memory led to installations with amounts of RAM approaching 4 GiB, and the use of virtual memory spaces exceeding the 4 GiB ceiling became desirable for handling certain types of problems. In response, MIPS and DEC developed 64-bit microprocessor architectures, initially for high-end
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 ...
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 ...
machines. By the mid-1990s, HAL Computer Systems,
Sun Microsystems Sun Microsystems, Inc. (Sun for short) was an American technology company that sold computers, computer components, software, and information technology services and created the Java programming language, the Solaris operating system, ZFS, t ...
, IBM,
Silicon Graphics Silicon Graphics, Inc. (stylized as SiliconGraphics before 1999, later rebranded SGI, historically known as Silicon Graphics Computer Systems or SGCS) was an American high-performance computing manufacturer, producing computer hardware and soft ...
, and Hewlett Packard had developed 64-bit architectures for their workstation and server systems. A notable exception to this trend were mainframes from IBM, which then used 32-bit data and 31-bit address sizes; the IBM mainframes did not include 64-bit processors until 2000. During the 1990s, several low-cost 64-bit microprocessors were used in consumer electronics and embedded applications. Notably, the Nintendo 64 and the PlayStation 2 had 64-bit microprocessors before their introduction in personal computers. High-end printers, network equipment, and industrial computers, also used 64-bit microprocessors, such as the
Quantum Effect Devices Quantum Effect Devices (QED) was a microprocessor design company incorporated in 1991 as Quantum Effect Design. It was based in Palo Alto, California. History The three founders, Tom Riordan, Earl Killian and Ray Kunita, were senior managers ...
R5000 The R5000 is a 64-bit, bi-endian, superscalar, in-order execution 2-issue design microprocessor, that implements the MIPS IV instruction set architecture (ISA) developed by Quantum Effect Design (QED) in 1996. The project was funded by MIPS Techn ...
. 64-bit computing started to trickle down to the personal computer desktop from 2003 onward, when some models in
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 Macintosh lines switched to PowerPC 970 processors (termed ''G5'' by Apple), and Advanced Micro Devices (AMD) released its first 64-bit x86-64 processor.


64-bit data timeline

;1961: IBM delivers the
IBM 7030 Stretch The IBM 7030, also known as Stretch, was IBM's first transistorized supercomputer. It was the fastest computer in the world from 1961 until the first CDC 6600 became operational in 1964."Designed by Seymour Cray, the CDC 6600 was almost three t ...
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 ...
, which uses 64-bit data words and 32- or 64-bit instruction words. ;1974:
Control Data Corporation Control Data Corporation (CDC) was a mainframe and supercomputer firm. CDC was one of the nine major United States computer companies through most of the 1960s; the others were IBM, Burroughs Corporation, DEC, NCR, General Electric, Honeywe ...
launches the CDC Star-100 vector supercomputer, which uses a 64-bit word architecture (prior CDC systems were based on a 60-bit architecture). : International Computers Limited launches the ICL 2900 Series with 32-bit, 64-bit, and 128-bit two's complement integers; 64-bit and 128-bit floating point; 32-bit, 64-bit, and 128-bit packed decimal and a 128-bit accumulator register. The architecture has survived through a succession of ICL and Fujitsu machines. The latest is the Fujitsu Supernova, which emulates the original environment on 64-bit Intel processors. ;1976:
Cray Research Cray Inc., a subsidiary of Hewlett Packard Enterprise, is an American supercomputer manufacturer headquartered in Seattle, Washington. It also manufactures systems for data storage and analytics. Several Cray supercomputer systems are listed ...
delivers the first
Cray-1 The Cray-1 was a supercomputer designed, manufactured and marketed by Cray Research. Announced in 1975, the first Cray-1 system was installed at Los Alamos National Laboratory in 1976. Eventually, over 100 Cray-1s were sold, making it one of the ...
supercomputer, which is based on a 64-bit word architecture and will form the basis for later Cray vector supercomputers. ;1983: Elxsi launches the Elxsi 6400 parallel
minisupercomputer Minisupercomputers constituted a short-lived class of computers that emerged in the mid-1980s, characterized by the combination of vector processing and small-scale multiprocessing. As scientific computing using vector processors became more po ...
. The Elxsi architecture has 64-bit data registers but a 32-bit address space. ;1989:
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 ...
introduces the Intel i860
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) processor. Marketed as a "64-Bit Microprocessor", it had essentially a 32-bit architecture, enhanced with a 3D graphics unit capable of 64-bit integer operations. ;1993:
Atari Atari () is a brand name that has been owned by several entities since its inception in 1972. It is currently owned by French publisher Atari SA through a subsidiary named Atari Interactive. The original Atari, Inc., founded in Sunnyvale, Ca ...
introduces the Atari Jaguar video game console, which includes some 64-bit wide data paths in its architecture.


64-bit address timeline

;1991:
MIPS Computer Systems MIPS Technologies, Inc., formerly MIPS Computer Systems, Inc., was an American fabless semiconductor design company that is most widely known for developing the MIPS architecture and a series of RISC CPU chips based on it. MIPS provides pro ...
produces the first 64-bit microprocessor, the R4000, which implements the MIPS III architecture, the third revision of its MIPS architecture. The CPU is used in SGI graphics workstations starting with the IRIS Crimson. Kendall Square Research deliver their first KSR1 supercomputer, based on a proprietary 64-bit RISC processor architecture running OSF/1. ;1992:
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 ...
(DEC) introduces the pure 64-bit
Alpha Alpha (uppercase , lowercase ; grc, ἄλφα, ''álpha'', or ell, άλφα, álfa) is the first letter of the Greek alphabet. In the system of Greek numerals, it has a value of one. Alpha is derived from the Phoenician letter aleph , whi ...
architecture which was born from the PRISM project. ;1994:
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 ...
announces plans for the 64-bit IA-64 architecture (jointly developed with
Hewlett-Packard The Hewlett-Packard Company, commonly shortened to Hewlett-Packard ( ) or HP, was an American multinational information technology company headquartered in Palo Alto, California. HP developed and provided a wide variety of hardware components ...
) as a successor to its 32-bit
IA-32 IA-32 (short for "Intel Architecture, 32-bit", commonly called i386) is the 32-bit version of the x86 instruction set architecture, designed by Intel and first implemented in the 80386 microprocessor in 1985. IA-32 is the first incarnatio ...
processors. A 1998 to 1999 launch date was targeted. ;1995: Sun launches a 64-bit
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 develope ...
processor, the
UltraSPARC The UltraSPARC is a microprocessor developed by Sun Microsystems and fabricated by Texas Instruments, introduced in mid-1995. It is the first microprocessor from Sun to implement the 64-bit SPARC V9 instruction set architecture (ISA). Marc Tre ...
.
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 ...
-owned HAL Computer Systems launches workstations based on a 64-bit CPU, HAL's independently designed first-generation SPARC64. IBM releases the A10 and A30 microprocessors, the first 64-bit PowerPC AS processors. IBM also releases a 64-bit AS/400 system upgrade, which can convert the operating system, database and applications. ;1996: Nintendo introduces the Nintendo 64 video game console, built around a low-cost variant of the MIPS R4000. HP releases the first implementation of its 64-bit PA-RISC 2.0 architecture, the
PA-8000 The PA-8000 (PCX-U), code-named ''Onyx'', is a microprocessor developed and fabricated by Hewlett-Packard (HP) that implemented the PA-RISC 2.0 instruction set architecture (ISA). Hunt 1995 It was a completely new design with no circuitry deriv ...
. ;1998: IBM releases the POWER3 line of full-64-bit PowerPC/ POWER processors. ;1999: Intel releases the instruction set for the IA-64 architecture. AMD publicly discloses its set of 64-bit extensions to IA-32, called x86-64 (later branded AMD64). ;2000: IBM ships its first 64-bit
z/Architecture z/Architecture, initially and briefly called ESA Modal Extensions (ESAME), is IBM's 64-bit complex instruction set computer (CISC) instruction set architecture, implemented by its mainframe computers. IBM introduced its first z/Architect ...
mainframe, the zSeries z900. z/Architecture is a 64-bit version of the 32-bit
ESA/390 The IBM System/390 is a discontinued mainframe product family implementing the ESA/390, the fifth generation of the System/360 instruction set architecture. The first computers to use the ESA/390 were the Enterprise System/9000 (ES/9000 ...
architecture, a descendant of the 32-bit System/360 architecture. ;2001: Intel ships its IA-64 processor line, after repeated delays in getting to market. Now branded Itanium and targeting high-end servers, sales fail to meet expectations. ;2003: AMD introduces its Opteron and
Athlon 64 The Athlon 64 is a ninth-generation, AMD64-architecture microprocessor produced by Advanced Micro Devices (AMD), released on September 23, 2003. It is the third processor to bear the name ''Athlon'', and the immediate successor to the Athlon XP. T ...
processor lines, based on its AMD64 architecture which is the first x86-based 64-bit processor architecture.
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 ...
also ships the 64-bit "G5" PowerPC 970 CPU produced by IBM. Intel maintains that its Itanium chips would remain its only 64-bit processors. ;2004: Intel, reacting to the market success of AMD, admits it has been developing a clone of the AMD64 extensions named IA-32e (later renamed EM64T, then yet again renamed to Intel 64). Intel ships updated versions of its
Xeon Xeon ( ) is a brand of x86 microprocessors designed, manufactured, and marketed by Intel, targeted at the non-consumer workstation, server, and embedded system markets. It was introduced in June 1998. Xeon processors are based on the same ar ...
and
Pentium 4 Pentium 4 is a series of single-core CPUs for desktops, laptops and entry-level servers manufactured by Intel. The processors were shipped from November 20, 2000 until August 8, 2008. The production of Netburst processors was active from 2000 ...
processor families supporting the new 64-bit instruction set. : VIA Technologies announces the
Isaiah Isaiah ( or ; he, , ''Yəšaʿyāhū'', "God is Salvation"), also known as Isaias, was the 8th-century BC Israelite prophet after whom the Book of Isaiah is named. Within the text of the Book of Isaiah, Isaiah himself is referred to as "the ...
64-bit processor. ;2006: Sony, IBM, and Toshiba begin manufacturing the 64-bit
Cell processor Cell is a multi-core microprocessor microarchitecture that combines a general-purpose PowerPC core of modest performance with streamlined coprocessing elements which greatly accelerate multimedia and vector processing applications, as well as m ...
for use in the
PlayStation 3 The PlayStation 3 (PS3) is a home video game console developed by Sony Interactive Entertainment, Sony Computer Entertainment. The successor to the PlayStation 2, it is part of the PlayStation brand of consoles. It was first released on Novemb ...
, servers, workstations, and other appliances. Intel released Core 2 Duo as the first mainstream x86-64 processor for its mobile, desktop, and workstation line. Prior 64-bit extension processor lines were not widely available in the consumer retail market (most of 64-bit Pentium 4/D were OEM), 64-bit Pentium 4, Pentium D, and Celeron were not into mass production until late 2006 due to poor yield issue (most of good yield wafers were targeted at server and mainframe while mainstream still remain 130 nm 32-bit processor line until 2006) and soon became low end after Core 2 debuted. AMD released their first 64-bit mobile processor and manufactured in 90 nm. ;2011: ARM Holdings announces ARMv8-A, the first 64-bit version of the ARM architecture family. ;2012: ARM Holdings announced their Cortex-A53 and Cortex-A57 cores, their first cores based on their 64-bit architecture, on 30 October 2012. ;2013:Apple announces the iPhone 5S, with the world's first 64-bit processor in a smartphone, which uses their A7 ARMv8-A-based system-on-a-chip alongside the iPad Air and iPad Mini 2 which are the world's first 64-bit processor in a tablet. ;2014:Google announces the Nexus 9 tablet, the first Android device to run on the 64-bit Tegra K1 chip. ;2015:Apple announces the iPod Touch (6th generation), the first iPod Touch to use the 64-bit processor A8 ARMv8-A-based system-on-a-chip alongside the Apple TV (4th generation) which is the world's first 64-bit processor in an Apple TV. ;2018:Apple announces the
Apple Watch Series 4 Apple Watch is a line of smartwatches produced by Apple Inc. It incorporates fitness tracking, health-oriented capabilities, and wireless telecommunication, and integrates with iOS and other Apple products and services. The Apple Watch was re ...
, the first Apple Watch to use the 64-bit processor S4 ARMv8-A-based system-on-a-chip. ;2020:Synopsis announce the ARCv3 ISA, the first 64-bit version of the ARC ISA.


64-bit operating system timeline

;1985:
Cray Cray Inc., a subsidiary of Hewlett Packard Enterprise, is an American supercomputer manufacturer headquartered in Seattle, Washington. It also manufactures systems for data storage and analytics. Several Cray supercomputer systems are listed i ...
releases
UNICOS UNICOS is a range of Unix and after it Linux operating system (OS) variants developed by Cray for its supercomputers. UNICOS is the successor of the Cray Operating System (COS). It provides network clustering and source code compatibility lay ...
, the first 64-bit implementation of the
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, ...
operating system. ;1993: DEC releases the 64-bit DEC OSF/1 AXP
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 system (later renamed Tru64 UNIX) for its systems based on the
Alpha Alpha (uppercase , lowercase ; grc, ἄλφα, ''álpha'', or ell, άλφα, álfa) is the first letter of the Greek alphabet. In the system of Greek numerals, it has a value of one. Alpha is derived from the Phoenician letter aleph , whi ...
architecture. ;1994: Support for the
R8000 The R8000 is a microprocessor chipset developed by MIPS Technologies, Inc. (MTI), Toshiba, and Weitek.Hsu 1994 It was the first implementation of the MIPS IV instruction set architecture. The R8000 is also known as the ''TFP'', for ''Tremendous F ...
processor is added by
Silicon Graphics Silicon Graphics, Inc. (stylized as SiliconGraphics before 1999, later rebranded SGI, historically known as Silicon Graphics Computer Systems or SGCS) was an American high-performance computing manufacturer, producing computer hardware and soft ...
to the
IRIX IRIX ( ) is a discontinued operating system developed by Silicon Graphics (SGI) to run on the company's proprietary MIPS workstations and servers. It is based on UNIX System V with BSD extensions. In IRIX, SGI originated the XFS file system a ...
operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ef ...
in release 6.0. ;1995: DEC releases
OpenVMS OpenVMS, often referred to as just VMS, is a multi-user, multiprocessing and virtual memory-based operating system. It is designed to support time-sharing, batch processing, transaction processing and workstation applications. Customers using Ope ...
7.0, the first full 64-bit version of OpenVMS for Alpha. First 64-bit Linux distribution for the Alpha architecture is released. ;1996: Support for the R4x00 processors in 64-bit mode is added by
Silicon Graphics Silicon Graphics, Inc. (stylized as SiliconGraphics before 1999, later rebranded SGI, historically known as Silicon Graphics Computer Systems or SGCS) was an American high-performance computing manufacturer, producing computer hardware and soft ...
to the
IRIX IRIX ( ) is a discontinued operating system developed by Silicon Graphics (SGI) to run on the company's proprietary MIPS workstations and servers. It is based on UNIX System V with BSD extensions. In IRIX, SGI originated the XFS file system a ...
operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ef ...
in release 6.2. ;1998: Sun releases Solaris 7, with full 64-bit
UltraSPARC The UltraSPARC is a microprocessor developed by Sun Microsystems and fabricated by Texas Instruments, introduced in mid-1995. It is the first microprocessor from Sun to implement the 64-bit SPARC V9 instruction set architecture (ISA). Marc Tre ...
support. ;2000: IBM releases z/OS, a 64-bit operating system descended from MVS, for the new zSeries 64-bit mainframes; 64-bit
Linux on z Systems 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, which in ...
follows the CPU release almost immediately. ;2001: Linux becomes the first OS kernel to fully support x86-64 (on a simulator, as no x86-64 processors had been released yet). ;2001: Microsoft releases
Windows XP 64-Bit Edition Windows XP, which is the next version of Windows NT after Windows 2000 and the successor to the consumer-oriented Windows Me, has been released in several editions since its original release in 2001. Windows XP is available in many languages. In ...
for the Itanium's IA-64 architecture; it could run
32-bit application 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 ...
s through an execution layer. ;2003: Apple releases its
Mac OS X 10.3 Mac OS X Panther (version 10.3) is the fourth major release of macOS, Apple's desktop and server operating system. It followed Mac OS X Jaguar and preceded Mac OS X Tiger. It was released on October 24, 2003. System requirements Panther's sy ...
"Panther" operating system which adds support for native 64-bit integer arithmetic on PowerPC 970 processors. 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 release with support for AMD64.
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 ...
releases with support for AMD64. ;2005: On January 4, Microsoft discontinues Windows XP 64-Bit Edition, as no PCs with IA-64 processors had been available since the previous September, and announces that it is developing x86-64 versions of Windows to replace it. On January 31, Sun releases
Solaris 10 Solaris is a proprietary Unix operating system originally developed by Sun Microsystems. After the Sun acquisition by Oracle in 2010, it was renamed Oracle Solaris. Solaris superseded the company's earlier SunOS in 1993, and became known fo ...
with support for AMD64 and EM64T processors. On April 29, Apple releases Mac OS X 10.4 "Tiger" which provides limited support for 64-bit command-line applications on machines with PowerPC 970 processors; later versions for Intel-based Macs supported 64-bit command-line applications on Macs with EM64T processors. On April 30, Microsoft releases Windows XP Professional x64 Edition and Windows Server 2003 x64 Edition for AMD64 and EM64T processors. ;2006: Microsoft releases Windows Vista, including a 64-bit version for AMD64/EM64T processors that retains 32-bit compatibility. In the 64-bit version, all Windows applications and components are 64-bit, although many also have their 32-bit versions included for compatibility with plug-ins. ;2007: Apple releases
Mac OS X 10.5 Mac OS X Leopard (version 10.5) is the sixth software versioning, major release of macOS, Apple Inc., Apple's desktop and server operating system for Macintosh computers. Leopard was released on October 26, 2007 as the successor of Mac OS X Tig ...
"Leopard", which fully supports 64-bit applications on machines with PowerPC 970 or EM64T processors. ;2009: Microsoft releases
Windows 7 Windows 7 is a major release of the Windows NT operating system developed by Microsoft. It was Software release life cycle#Release to manufacturing (RTM), released to manufacturing on July 22, 2009, and became generally available on October 22, ...
, which, like Windows Vista, includes a full 64-bit version for AMD64/Intel 64 processors; most new computers are loaded by default with a 64-bit version. Microsoft also releases Windows Server 2008 R2, which is the first 64-bit only server operating system. Apple releases Mac OS X 10.6, "Snow Leopard", which ships with a 64-bit kernel for AMD64/Intel64 processors, although only certain recent models of Apple computers will run the 64-bit kernel by default. Most applications bundled with Mac OS X 10.6 are now also 64-bit. ;2011: Apple releases Mac OS X 10.7, "Lion", which runs the 64-bit kernel by default on supported machines. Older machines that are unable to run the 64-bit kernel run the 32-bit kernel, but, as with earlier releases, can still run 64-bit applications; Lion does not support machines with 32-bit processors. Nearly all applications bundled with Mac OS X 10.7 are now also 64-bit, including iTunes. ;2012: Microsoft releases
Windows 8 Windows 8 is a major release of the Windows NT operating system developed by Microsoft. It was released to manufacturing on August 1, 2012; it was subsequently made available for download via MSDN and TechNet on August 15, 2012, and later to ...
which supports UEFI Class 3 (
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 ...
without CSM) and Secure Boot. ;2013: Apple releases iOS 7, which, on machines with AArch64 processors, has a 64-bit kernel that supports 64-bit applications. ;2014: Google releases Android Lollipop, the first version of the Android operating system with support for 64-bit processors. ;2017: Apple releases iOS 11, supporting only machines with AArch64 processors. It has a 64-bit kernel that only supports 64-bit applications. 32-bit applications are no longer compatible. ;2018: Apple releases watchOS 5, the first watchOS version to bring the 64-bit support. ;2019: Apple releases macOS 10.15 "Catalina", dropping support for 32-bit Intel applications. ;2021: Google releases
Android 12 Android 12 is the twelfth major release and 19th version of Android, the mobile operating system developed by the Open Handset Alliance led by Google. The first beta was released on May 18, 2021. Android 12 was released publicly on October ...
, dropping support for 32-bit applications. Microsoft releases Windows 11 on October 5, which only supports 64-bit systems, dropping support for IA-32 systems. ;2022: Apple releases
watchOS 9 watchOS is the operating system of the Apple Watch, developed by Apple Inc. It is based on iOS, the operating system used by the iPhone, and has many similar features. It was released on April 24, 2015, along with the Apple Watch, the only dev ...
, the first watchOS version to run exclusively on the Apple Watch models with 64-bit processors (including Apple Watch Series 4 or newer, Apple Watch SE (1st generation) or newer and the newly introduced Apple Watch Ultra), dropping support for
Apple Watch Series 3 Apple Watch is a line of smartwatches produced by Apple Inc. It incorporates fitness tracking, health-oriented capabilities, and wireless telecommunication, and integrates with iOS and other Apple products and services. The Apple Watch was rel ...
as the final Apple Watch model with 32-bit processor.


Limits of processors

In principle, a 64-bit microprocessor can address 16 EiB (, or about 18.4 exabytes) of memory. However, not all instruction sets, and not all processors implementing those instruction sets, support a full 64-bit virtual or physical address space. The x86-64 architecture () allows 48 bits for virtual memory and, for any given processor, up to 52 bits for physical memory. These limits allow memory sizes of 256  TiB () and 4  PiB (), respectively. A PC cannot currently contain 4  pebibytes of memory (due to the physical size of the memory chips), but AMD envisioned large servers, shared memory clusters, and other uses of physical address space that might approach this in the foreseeable future. Thus the 52-bit physical address provides ample room for expansion while not incurring the cost of implementing full 64-bit physical addresses. Similarly, the 48-bit virtual address space was designed to provide 65,536 (216) times the 32-bit limit of 4 GiB (), allowing room for later expansion and incurring no overhead of translating full 64-bit addresses. The Power ISA v3.0 allows 64 bits for an effective address, mapped to a segmented address with between 65 and 78 bits allowed, for virtual memory, and, for any given processor, up to 60 bits for physical memory. The Oracle
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 develope ...
Architecture 2015 allows 64 bits for virtual memory and, for any given processor, between 40 and 56 bits for physical memory. The ARM AArch64 Virtual Memory System Architecture allows 48 bits for virtual memory and, for any given processor, from 32 to 48 bits for physical memory. The
DEC Alpha Alpha (original name Alpha AXP) is a 64-bit reduced instruction set computer (RISC) instruction set architecture (ISA) developed by Digital Equipment Corporation (DEC). Alpha was designed to replace 32-bit VAX complex instruction set compute ...
specification requires minimum of 43 bits of virtual memory address space (8 TiB) to be supported, and hardware need to check and trap if the remaining unsupported bits are zero (to support compatibility on future processors). Alpha 21064 supported 43 bits of virtual memory address space (8 TiB) and 34 bits of physical memory address space (16 GiB). Alpha 21164 supported 43 bits of virtual memory address space (8 TiB) and 40 bits of physical memory address space (1 TiB). Alpha 21264 supported user-configurable 43 or 48 bits of virtual memory address space (8 TiB or 256 TiB) and 44 bits of physical memory address space (16 TiB).


64-bit applications


32-bit vs 64-bit

A change from 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 ...
to a 64-bit architecture is a fundamental alteration, as most
operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ef ...
s must be extensively modified to take advantage of the new architecture, because that software has to manage the actual memory addressing hardware. Other software must also be ported to use the new abilities; older 32-bit software may be supported either by virtue of the 64-bit instruction set being a superset of the 32-bit instruction set, so that processors that support the 64-bit instruction set can also run code for the 32-bit instruction set, or through software emulation, or by the actual implementation of a 32-bit processor core within the 64-bit processor, as with some Itanium processors from Intel, which included an
IA-32 IA-32 (short for "Intel Architecture, 32-bit", commonly called i386) is the 32-bit version of the x86 instruction set architecture, designed by Intel and first implemented in the 80386 microprocessor in 1985. IA-32 is the first incarnatio ...
processor core to run 32-bit x86 applications. The operating systems for those 64-bit architectures generally support both 32-bit and 64-bit applications. One significant exception to this is the IBM AS/400, software for which is compiled into a virtual
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 ...
(ISA) called ''Technology Independent Machine Interface'' (TIMI); TIMI code is then translated to native machine code by low-level software before being executed. The translation software is all that must be rewritten to move the full OS and all software to a new platform, as when IBM transitioned the native instruction set for AS/400 from the older 32/48-bit ''IMPI'' to the newer 64-bit ''PowerPC-AS'', codenamed ''Amazon''. The IMPI instruction set was quite different from even 32-bit PowerPC, so this transition was even bigger than moving a given instruction set from 32 to 64 bits. On 64-bit hardware with x86-64 architecture (AMD64), most 32-bit operating systems and applications can run with no compatibility issues. While the larger address space of 64-bit architectures makes working with large data sets in applications such as
digital video Digital video is an electronic representation of moving visual images (video) in the form of encoded digital data Digital data, in information theory and information systems, is information represented as a string of discrete symbols eac ...
, scientific computing, and large
database In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases ...
s easier, there has been considerable debate on whether they or their 32-bit compatibility modes will be faster than comparably priced 32-bit systems for other tasks. A compiled Java program can run on a 32- or 64-bit Java virtual machine with no modification. The lengths and precision of all the built-in types, such as char, short, int, long, float, and double, and the types that can be used as array indices, are specified by the standard and are not dependent on the underlying architecture. Java programs that run on a 64-bit Java virtual machine have access to a larger address space. Speed is not the only factor to consider in comparing 32-bit and 64-bit processors. Applications such as multi-tasking, stress testing, and clustering – for
high-performance computing High-performance computing (HPC) uses supercomputers and computer clusters to solve advanced computation problems. Overview HPC integrates systems administration (including network and security knowledge) and parallel programming into a mult ...
(HPC) – may be more suited to a 64-bit architecture when deployed appropriately. For this reason, 64-bit clusters have been widely deployed in large organizations, such as IBM, HP, and Microsoft. Summary: *A 64-bit processor performs best with 64-bit software. *A 64-bit processor may have
backward compatibility Backward compatibility (sometimes known as backwards compatibility) is a property of an operating system, product, or technology that allows for interoperability with an older legacy system, or with input designed for such a system, especiall ...
, allowing it to run 32-bit application software for the 32-bit version of its instruction set, and may also support running 32-bit operating systems for the 32-bit version of its instruction set. *A 32-bit processor is incompatible with 64-bit software.


Pros and cons

A common misconception is that 64-bit architectures are no better than 32-bit architectures unless the computer has more than 4 GiB of
random-access memory Random-access memory (RAM; ) is a form of computer memory that can be read and changed in any order, typically used to store working data and machine code. A random-access memory device allows data items to be read or written in almost the ...
. This is not entirely true: *Some operating systems and certain hardware configurations limit the physical memory space to 3 GiB on
IA-32 IA-32 (short for "Intel Architecture, 32-bit", commonly called i386) is the 32-bit version of the x86 instruction set architecture, designed by Intel and first implemented in the 80386 microprocessor in 1985. IA-32 is the first incarnatio ...
systems, due to much of the 3–4 GiB region being reserved for hardware addressing; see 3 GiB barrier; 64-bit architectures can address far more than 4 GiB. However, IA-32 processors from the Pentium Pro onward allow a 36-bit ''physical'' memory address space, using Physical Address Extension (PAE), which gives a 64 GiB physical address range, of which up to 62 GiB may be used by main memory; operating systems that support PAE may not be limited to 4 GiB of physical memory, even on IA-32 processors. However, drivers and other kernel mode software, more so older versions, may be incompatible with PAE; this has been cited as the reason for 32-bit versions of
Microsoft 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 ...
being limited to 4 GiB of physical RAM (although the validity of this explanation has been disputed). *Some operating systems reserve portions of process
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 ...
for OS use, effectively reducing the total address space available for mapping memory for user programs. For instance, 32-bit Windows reserves 1 or 2 GiB (depending on the settings) of the total address space for the kernel, which leaves only 3 or 2 GiB (respectively) of the address space available for user mode. This limit is much higher on 64-bit operating systems. * Memory-mapped files are becoming more difficult to implement in 32-bit architectures as files of over 4 GiB become more common; such large files cannot be memory-mapped easily to 32-bit architectures, as only part of the file can be mapped into the address space at a time, and to access such a file by memory mapping, the parts mapped must be swapped into and out of the address space as needed. This is a problem, as memory mapping, if properly implemented by the OS, is one of the most efficient disk-to-memory methods. *Some 64-bit programs, such as encoders, decoders and encryption software, can benefit greatly from 64-bit registers, while the performance of other programs, such as 3D graphics-oriented ones, remains unaffected when switching from a 32-bit to a 64-bit environment. *Some 64-bit architectures, such as x86-64 and AArch64, support more general-purpose registers than their 32-bit counterparts (although this is not due specifically to the word length). This leads to a significant speed increase for tight loops since the processor does not have to fetch data from the cache or main memory if the data can fit in the available registers. :Example in C: int a, b, c, d, e; for (a = 0; a < 100; a++) : This code first creates 5 values: a, b, c, d and e; and then puts them in a loop. During the loop, this code changes the value of b to the value of a, the value of c to the value of b, the value of d to the value of c and the value of e to the value of d. This has the same effect as changing all the values to a. :If a processor can keep only two or three values or variables in registers, it would need to move some values between memory and registers to be able to process variables d and e also; this is a process that takes many CPU cycles. A processor that can hold all values and variables in registers can loop through them with no need to move data between registers and memory for each iteration. This behavior can easily be compared with virtual memory, although any effects are contingent on the compiler. The main disadvantage of 64-bit architectures is that, relative to 32-bit architectures, the same data occupies more space in memory (due to longer pointers and possibly other types, and alignment padding). This increases the memory requirements of a given process and can have implications for efficient processor cache use. Maintaining a partial 32-bit model is one way to handle this, and is in general reasonably effective. For example, the z/OS operating system takes this approach, requiring program code to reside in 31-bit address spaces (the high order bit is not used in address calculation on the underlying hardware platform) while data objects can optionally reside in 64-bit regions. Not all such applications require a large address space or manipulate 64-bit data items, so these applications do not benefit from these features.


Software availability

x86-based 64-bit systems sometimes lack equivalents of
software Software is a set of computer programs and associated documentation and data. This is in contrast to hardware, from which the system is built and which actually performs the work. At the lowest programming level, executable code consist ...
that is written for 32-bit architectures. The most severe problem in Microsoft Windows is incompatible device drivers for obsolete hardware. Most 32-bit application software can run on a 64-bit operating system in a compatibility mode, also termed an emulation mode, e.g., Microsoft
WoW64 In computing on Microsoft platforms, WoW64 (Windows 32-bit on Windows 64-bit) is a subsystem of the Windows operating system capable of running 32-bit applications on 64-bit Windows. It is included in all 64-bit versions of Windows—includi ...
Technology for IA-64 and AMD64. The 64-bit Windows Native Mode driver environment runs atop 64-bit , which cannot call 32-bit Win32 subsystem code (often devices whose actual hardware function is emulated in user mode software, like Winprinters). Because 64-bit drivers for most devices were unavailable until early 2007 (Vista x64), using a 64-bit version of Windows was considered a challenge. However, the trend has since moved toward 64-bit computing, more so as memory prices dropped and the use of more than 4 GiB of RAM increased. Most manufacturers started to provide both 32-bit and 64-bit drivers for new devices, so unavailability of 64-bit drivers ceased to be a problem. 64-bit drivers were not provided for many older devices, which could consequently not be used in 64-bit systems. Driver compatibility was less of a problem with open-source drivers, as 32-bit ones could be modified for 64-bit use. Support for hardware made before early 2007, was problematic for open-source platforms, due to the relatively small number of users. 64-bit versions of Windows cannot run 16-bit software. However, most 32-bit applications will work well. 64-bit users are forced to install a
virtual machine In computing, a virtual machine (VM) is the virtualization/ emulation of a computer system. Virtual machines are based on computer architectures and provide functionality of a physical computer. Their implementations may involve specialized h ...
of a 16- or 32-bit operating system to run 16-bit applications. Mac OS X 10.4 "Tiger" and
Mac OS X 10.5 Mac OS X Leopard (version 10.5) is the sixth software versioning, major release of macOS, Apple Inc., Apple's desktop and server operating system for Macintosh computers. Leopard was released on October 26, 2007 as the successor of Mac OS X Tig ...
"Leopard" had only a 32-bit kernel, but they can run 64-bit user-mode code on 64-bit processors. Mac OS X 10.6 "Snow Leopard" had both 32- and 64-bit kernels, and, on most Macs, used the 32-bit kernel even on 64-bit processors. This allowed those Macs to support 64-bit processes while still supporting 32-bit device drivers; although not 64-bit drivers and performance advantages that can come with them. Mac OS X 10.7 "Lion" ran with a 64-bit kernel on more Macs, and OS X 10.8 "Mountain Lion" and later
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 ...
releases only have a 64-bit kernel. On systems with 64-bit processors, both the 32- and 64-bit macOS kernels can run 32-bit user-mode code, and all versions of macOS up to macOS Mojave (10.14) include 32-bit versions of libraries that 32-bit applications would use, so 32-bit user-mode software for macOS will run on those systems. The 32-bit versions of libraries have been removed by Apple in macOS Catalina (10.15).
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 most other
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, and the C and C++ toolchains for them, have supported 64-bit processors for many years. Many applications and libraries for those platforms are
open-source software Open-source software (OSS) is computer software that is released under a license in which the copyright holder grants users the rights to use, study, change, and distribute the software and its source code to anyone and for any purpose. ...
, written in C and C++, so that if they are 64-bit-safe, they can be compiled into 64-bit versions. This source-based distribution model, with an emphasis on frequent releases, makes availability of application software for those operating systems less of an issue.


64-bit data models

In 32-bit programs, pointers and data types such as integers generally have the same length. This is not necessarily true on 64-bit machines. Mixing data types in programming languages such as C and its descendants such as C++ and Objective-C may thus work on 32-bit implementations but not on 64-bit implementations. In many programming environments for C and C-derived languages on 64-bit machines, int variables are still 32 bits wide, but long integers and pointers are 64 bits wide. These are described as having an ''LP64'' data model, which is an abbreviation of "Long, Pointer, 64". Other models are the ''ILP64'' data model in which all three data types are 64 bits wide, and even the ''SILP64'' model where ''short'' integers are also 64 bits wide. However, in most cases the modifications required are relatively minor and straightforward, and many well-written programs can simply be recompiled for the new environment with no changes. Another alternative is the ''LLP64'' model, which maintains compatibility with 32-bit code by leaving both int and long as 32-bit. ''LL'' refers to the ''long long integer'' type, which is at least 64 bits on all platforms, including 32-bit environments. There are also systems with 64-bit processors using an ''ILP32'' data model, with the addition of 64-bit long long integers; this is also used on many platforms with 32-bit processors. This model reduces code size and the size of data structures containing pointers, at the cost of a much smaller address space, a good choice for some embedded systems. For instruction sets such as x86 and ARM in which the 64-bit version of the instruction set has more registers than does the 32-bit version, it provides access to the additional registers without the space penalty. It is common in 64-bit RISC machines, explored in x86 as
x32 ABI The x32 ABI is an application binary interface (ABI) and one of the interfaces of the Linux kernel. The x32 ABI provides 32-bit integers, long and pointers (ILP32) on Intel and AMD 64-bit hardware. The ABI allows programs to take advantage of the b ...
, and has recently been used in the
Apple Watch Series 4 Apple Watch is a line of smartwatches produced by Apple Inc. It incorporates fitness tracking, health-oriented capabilities, and wireless telecommunication, and integrates with iOS and other Apple products and services. The Apple Watch was re ...
and 5. Many 64-bit platforms today use an ''LP64'' model (including Solaris,
AIX Aix or AIX may refer to: Computing * AIX, a line of IBM computer operating systems *An Alternate Index, for a Virtual Storage Access Method Key Sequenced Data Set * Athens Internet Exchange, a European Internet exchange point Places Belgiu ...
, HP-UX, Linux, macOS, BSD, and IBM z/OS). Microsoft Windows uses an ''LLP64'' model. The disadvantage of the LP64 model is that storing a long into an int truncates. On the other hand, converting a pointer to a long will “work” in LP64. In the LLP64 model, the reverse is true. These are not problems which affect fully standard-compliant code, but code is often written with implicit assumptions about the widths of data types. C code should prefer (u)intptr_t instead of long when casting pointers into integer objects. A programming model is a choice made to suit a given compiler, and several can coexist on the same OS. However, the programming model chosen as the primary model for the OS
application programming interface An application programming interface (API) is a way for two or more computer programs to communicate with each other. It is a type of software interface, offering a service to other pieces of software. A document or standard that describes how ...
(API) typically dominates. Another consideration is the data model used for device drivers. Drivers make up the majority of the operating system code in most modern operating systems (although many may not be loaded when the operating system is running). Many drivers use pointers heavily to manipulate data, and in some cases have to load pointers of a certain size into the hardware they support for direct memory access (DMA). As an example, a driver for a 32-bit PCI device asking the device to DMA data into upper areas of a 64-bit machine's memory could not satisfy requests from the operating system to load data from the device to memory above the 4 gibibyte barrier, because the pointers for those addresses would not fit into the DMA registers of the device. This problem is solved by having the OS take the memory restrictions of the device into account when generating requests to drivers for DMA, or by using an input–output memory management unit (IOMMU).


Current 64-bit architectures

, 64-bit architectures for which processors are being manufactured include: *The 64-bit extension created by Advanced Micro Devices (AMD) to Intel's x86 architecture (later licensed by Intel); commonly termed '' x86-64'', ''AMD64'', or ''x64'': **AMD's AMD64 extensions (used in
Athlon 64 The Athlon 64 is a ninth-generation, AMD64-architecture microprocessor produced by Advanced Micro Devices (AMD), released on September 23, 2003. It is the third processor to bear the name ''Athlon'', and the immediate successor to the Athlon XP. T ...
, Opteron, Sempron, Turion 64, Phenom, Athlon II, Phenom II, APU, FX, Ryzen, and
Epyc Epyc is a brand of multi-core x86-64 microprocessors designed and sold by AMD, based on the company's Zen microarchitecture. Introduced in June 2017, they are specifically targeted for the server and embedded system markets. Epyc processors share ...
processors) **
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 ...
's Intel 64 extensions, used in Intel Core 2/i3/i5/i7/i9, some
Atom Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Every solid, liquid, gas, a ...
, and newer
Celeron Celeron is Intel's brand name for low-end IA-32 and x86-64 computer microprocessor models targeted at low-cost personal computers. Celeron processors are compatible with IA-32 software. They typically offer less performance per clock speed co ...
, Pentium, and
Xeon Xeon ( ) is a brand of x86 microprocessors designed, manufactured, and marketed by Intel, targeted at the non-consumer workstation, server, and embedded system markets. It was introduced in June 1998. Xeon processors are based on the same ar ...
processors ***
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 ...
's K1OM architecture, a variant of ''Intel 64'' with no CMOV, MMX, and SSE instructions, used in first-generation Xeon Phi (Knights Corner) coprocessors, binary incompatible with x86-64 programs ** VIA Technologies' 64-bit extensions, used in the VIA Nano processors *IBM's
PowerPC PowerPC (with the backronym Performance Optimization With Enhanced RISC – Performance Computing, sometimes abbreviated as PPC) is a reduced instruction set computer (RISC) instruction set architecture (ISA) created by the 1991 Apple– IBM– ...
/
Power ISA Power ISA is a reduced instruction set computer (RISC) instruction set architecture (ISA) currently developed by the OpenPOWER Foundation, led by IBM. It was originally developed by IBM and the now-defunct Power.org industry group. Power ISA ...
: **IBM's POWER4, POWER5, POWER6, POWER7, POWER8, POWER9, and
IBM A2 The IBM A2 is an open source massively multicore capable and multithreaded 64-bit Power ISA processor core designed by IBM using the Power ISA v.2.06 specification. Versions of processors based on the A2 core range from a 2.3 GHz version with ...
processors *
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 develope ...
V9 architecture: **
Oracle An oracle is a person or agency considered to provide wise and insightful counsel or prophetic predictions, most notably including precognition of the future, inspired by deities. As such, it is a form of divination. Description The word ...
's M8 and S7 processors **
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 ...
's SPARC64 XII and
SPARC64 XIfx The SPARC64 V (''Zeus'') is a SPARC V9 microprocessor designed by Fujitsu. The SPARC64 V was the basis for a series of successive processors designed for servers, and later, supercomputers. The servers series are the SPARC64 V+, VI, VI+, VII, V ...
processors *IBM's
z/Architecture z/Architecture, initially and briefly called ESA Modal Extensions (ESAME), is IBM's 64-bit complex instruction set computer (CISC) instruction set architecture, implemented by its mainframe computers. IBM introduced its first z/Architect ...
, a 64-bit version of the
ESA/390 The IBM System/390 is a discontinued mainframe product family implementing the ESA/390, the fifth generation of the System/360 instruction set architecture. The first computers to use the ESA/390 were the Enterprise System/9000 (ES/9000 ...
architecture, used in IBM's eServer zSeries and System z mainframes: **IBM z13 and z14 **
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 ...
AP8000E *HP–Intel's IA-64 architecture: **Intel's Itanium processors (discontinued) *
MIPS Technologies MIPS Technologies, Inc., formerly MIPS Computer Systems, Inc., was an American fabless semiconductor design company that is most widely known for developing the MIPS architecture and a series of RISC CPU chips based on it. MIPS provides pro ...
'
MIPS64 MIPS (Microprocessor without Interlocked Pipelined Stages) is a family of reduced instruction set computer (RISC) instruction set architectures (ISA)Price, Charles (September 1995). ''MIPS IV Instruction Set'' (Revision 3.2), MIPS Technologies, ...
architecture * ARM Holdings' AArch64 architecture * Elbrus architecture: ** Elbrus-8S *
NEC SX architecture is a Japanese multinational information technology and electronics corporation, headquartered in Minato, Tokyo. The company was known as the Nippon Electric Company, Limited, before rebranding in 1983 as NEC. It provides IT and network soluti ...
** SX-Aurora TSUBASA *
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 ...
* ARC (processor) Most architectures of 64 bits that are derived from the same architecture of 32 bits can execute code written for the 32-bit versions natively, with no performance penalty. This kind of support is commonly called ''bi-arch support'' or more generally ''multi-arch support''.


See also

*
Computer memory In computing, memory is a device or system that is used to store information for immediate use in a computer or related computer hardware and digital electronic devices. The term ''memory'' is often synonymous with the term '' primary storag ...


Notes


References


External links


64-bit Transition Guide, Mac Developer Library
* *
Lessons on development of 64-bit C/C++ applicationsAMD64 (EM64T) architecture
{{Authority control 64-bit computers Data unit