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The IBM System/360 (S/360) is a family of
mainframe computer A mainframe computer, informally called a mainframe or big iron, is a computer used primarily by large organizations for critical applications like bulk data processing for tasks such as censuses, industry and consumer statistics, enterpris ...
systems that was announced by IBM on April 7, 1964, and delivered between 1965 and 1978. It was the first family of computers designed to cover both commercial and scientific applications and to cover a complete range of applications from small to large. The design distinguished between
architecture Architecture is the art and technique of designing and building, as distinguished from the skills associated with construction. It is both the process and the product of sketching, conceiving, planning, designing, and constructing building ...
and implementation, allowing IBM to release a suite of compatible designs at different prices. All but the only partially compatible Model 44 and the most expensive systems use
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 laye ...
to implement the instruction set, which features
8-bit In computer architecture, 8-bit Integer (computer science), integers or other Data (computing), data units are those that are 8 bits wide (1 octet (computing), octet). Also, 8-bit central processing unit (CPU) and arithmetic logic unit (ALU) arc ...
byte addressing and binary, decimal, and
hexadecimal In mathematics and computing, the hexadecimal (also base-16 or simply hex) numeral system is a positional numeral system that represents numbers using a radix (base) of 16. Unlike the decimal system representing numbers using 10 symbols, hexa ...
floating-point 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 b ...
calculations. The System/360 family introduced IBM's
Solid Logic Technology Solid Logic Technology (SLT) was IBM's method for hybrid packaging of electronic circuitry introduced in 1964 with the IBM System/360 series of computers and related machines. IBM chose to design custom hybrid circuits using discrete, flip chi ...
(SLT), which packed more transistors onto a circuit card, allowing more powerful but smaller computers to be built. The slowest System/360 model announced in 1964, the Model 30, could perform up to 34,500 instructions per second, with memory from 8 to 64  KB. High-performance models came later. The 1967
IBM System/360 Model 91 The IBM System/360 Model 91 was announced in 1964 as a competitor to the CDC 6600. Functionally, the Model 91 ran like any other large-scale System/360, but the internal organization was the most advanced of the System/360 line, and it was the ...
could execute up to 16.6
million instructions per second Instructions per second (IPS) is a measure of a computer's processor speed. For complex instruction set computers (CISCs), different instructions take different amounts of time, so the value measured depends on the instruction mix; even for compa ...
. The larger 360 models could have up to 8  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 computer ...
, though that much main memory was unusual—a large installation might have as little as 256 KB of main storage, but 512 KB, 768 KB or 1024 KB was more common. Up to 8 megabytes of slower (8 microsecond) Large Capacity Storage (LCS) was also available for some models. The IBM 360 was extremely successful in the market, allowing customers to purchase a smaller system with the knowledge they would be able to move to larger ones if their needs grew, without reprogramming application software or replacing peripheral devices. Its design influenced computer design for years to come; many consider it one of the most successful computers in history. The chief architect of System/360 was
Gene Amdahl Gene Myron Amdahl (November 16, 1922 – November 10, 2015) was an American computer architect and high-tech entrepreneur, chiefly known for his work on mainframe computers at IBM and later his own companies, especially Amdahl Corporation ...
, and the project was managed by
Fred Brooks Frederick Phillips Brooks Jr. (April 19, 1931 – November 17, 2022) was an American computer architect, software engineer, and computer scientist, best known for managing the development of IBM's System/360 family of computers and the O ...
, responsible to Chairman
Thomas J. Watson Jr. Thomas John Watson Jr. (January 14, 1914 – December 31, 1993) was an American businessman, political figure, Army Air Forces pilot, and philanthropist. The son of IBM Corporation founder Thomas J. Watson, he was the second IBM president (195 ...
"System/360 Announcement" (press release), IBM Data Processing Division, April 7, 1964, webpage
IBM-PR360
states cycle time from "...millionth-of-a-second to only 200 billionths-of-a-second," and "...memory capacity ranges from 8,000 characters of information to more than 8,000,000."
The commercial release was piloted by another of Watson's lieutenants,
John R. Opel John Roberts Opel (January 5, 1925, in Kansas City, Missouri – November 3, 2011, in Fort Myers, Florida) was a U.S. computer businessman. He served eleven years as the President of IBM between 1974 and 1985. He was the chief executive officer ...
, who managed the launch of IBM’s System 360 mainframe family in 1964. Application-level compatibility (with some restrictions) for System/360 software is maintained to the present day with the
System z IBM Z is a family name used by IBM for all of its z/Architecture mainframe computers. In July 2017, with another generation of products, the official family was changed to IBM Z from IBM z Systems; the IBM Z family now includes the newest mode ...
mainframe servers.


System/360 history


A family of computers

Contrasting with industry practice of the day, IBM created an entire new series of computers, from small to large, low- to high-performance, all using the same instruction set (with two exceptions for specific markets). This feat allowed customers to use a cheaper model and then upgrade to larger systems as their needs increased without the time and expense of rewriting software. Before the introduction of System/360, business and scientific applications used different computers with different instruction sets and operating systems. Different-sized computers also had their own instruction sets. IBM was the first manufacturer to exploit
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 laye ...
technology to implement a compatible range of computers of widely differing performance, although the largest, fastest models had hard-wired logic instead. This flexibility greatly lowered barriers to entry. With most other vendors customers had to choose between machines they could outgrow and machines that were potentially too powerful and thus too costly. This meant that many companies simply did not buy computers.


Models

IBM initially announced a series of six computers and forty common peripherals. IBM eventually delivered fourteen models, including rare one-off models for
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. The least expensive model was the Model 20 with as little as 4096 bytes of
core memory Core or cores may refer to: Science and technology * Core (anatomy), everything except the appendages * Core (manufacturing), used in casting and molding * Core (optical fiber), the signal-carrying portion of an optical fiber * Core, the central ...
, eight 16-bit registers instead of the sixteen 32-bit registers of other System/360 models, and an
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 ' ...
that was a subset of that used by the rest of the range. The initial announcement in 1964 included Models 30, 40, 50, 60, 62, and 70. The first three were low- to middle-range systems aimed at the
IBM 1400 series The IBM 1400 series were second-generation (transistor) mid-range business decimal computers that IBM marketed in the early 1960s. The computers were offered to replace tabulating machines like the IBM 407. The 1400-series machines stored infor ...
market. All three first shipped in mid-1965. The last three, intended to replace the
7000 series 7000 series may refer to: Japanese trains * Chichibu Railway 7000 series electric multiple unit (EMU) * Echizen Railway 7000 series EMU * Hankyu 7000 series EMU * Hokushin Kyuko Electric Railway 7000 series EMU operating for the Kobe Municipal Su ...
machines, never shipped and were replaced with the 65 and 75, which were first delivered in November 1965, and January 1966, respectively. Later additions to the low-end included models 20 (1966, mentioned above), 22 (1971), and 25 (1968). The Model 20 had several sub-models; sub-model 5 was at the higher end of the model. The Model 22 was a recycled Model 30 with minor limitations: a smaller maximum memory configuration, and slower I/O channels, which limited it to slower and lower-capacity disk and tape devices than on the 30. The Model 44 (1966) was a specialized model, designed for scientific computing and for real-time computing and process control, featuring some additional instructions, and with all storage-to-storage instructions and five other complex instructions eliminated. A succession of high-end machines included the Model 67 (1966, mentioned below, briefly anticipated as the 64 and 66), 85 (1969), 91 (1967, anticipated as the 92), 95 (1968), and 195 (1971). The 85 design was intermediate between the System/360 line and the follow-on
System/370 The IBM System/370 (S/370) is a model range of IBM mainframe computers announced on June 30, 1970, as the successors to the System/360 family. The series mostly maintains backward compatibility with the S/360, allowing an easy migration path f ...
and was the basis for the 370/165. There was a System/370 version of the 195, but it did not include Dynamic Address Translation. The implementations differed substantially, using different native data path widths, presence or absence of microcode, yet were extremely compatible. Except where specifically documented, the models were architecturally compatible. The 91, for example, was designed for scientific computing and provided out-of-order instruction execution (and could yield "imprecise interrupts" if a program trap occurred while several instructions were being read), but lacked the decimal instruction set used in commercial applications. New features could be added without violating architectural definitions: the 65 had a dual-processor version (M65MP) with extensions for inter-CPU signalling; the 85 introduced cache memory. Models 44, 75, 91, 95, and 195 were implemented with hardwired logic, rather than microcoded as all other models. The Model 67, announced in August 1965, was the first production IBM system to offer dynamic address translation (virtual memory) hardware to support
time-sharing In computing, time-sharing is the sharing of a computing resource among many users at the same time by means of multiprogramming and multi-tasking.DEC Timesharing (1965), by Peter Clark, The DEC Professional, Volume 1, Number 1 Its emergence a ...
. "DAT" is now more commonly referred to as an MMU. An experimental one-off unit was built based on a model 40. Before the 67, IBM had announced models 64 and 66, DAT versions of the 60 and 62, but they were almost immediately replaced with the 67 at the same time that the 60 and 62 were replaced with the 65. DAT hardware would reappear in the
S/370 The IBM System/370 (S/370) is a model range of IBM mainframe computers announced on June 30, 1970, as the successors to the System/360 family. The series mostly maintains backward compatibility with the S/360, allowing an easy migration path f ...
series in 1972, though it was initially absent from the series. Like its close relative, the 65, the 67 also offered dual CPUs. IBM stopped marketing all System/360 models by the end of 1977.


Backward compatibility

IBM's existing customers had a large investment in software that executed on second-generation machines. Several models offered the option of
emulation Emulation may refer to: *Emulation (computing), imitation of behavior of a computer or other electronic system with the help of another type of system :*Video game console emulator, software which emulates video game consoles *Gaussian process em ...
of the customer's previous computer using a combination of special hardware, special
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 laye ...
and an emulation program that used the emulation instructions to simulate the target system, so that old programs could run on the new machine. Customers initially had to halt the computer and load the emulation program. IBM later added features and modified emulator programs to allow emulation of the 1401, 1440, 1460, 1410 and 7010 under the control of an operating system. The Model 85 and later System/370 maintained the precedent, retaining emulation options and allowing emulator programs to execute under operating system control alongside native programs.


Successors and variants

System/360 (excepting the Model 20) was replaced with the compatible
System/370 The IBM System/370 (S/370) is a model range of IBM mainframe computers announced on June 30, 1970, as the successors to the System/360 family. The series mostly maintains backward compatibility with the S/360, allowing an easy migration path f ...
range in 1970 and Model 20 users were targeted to move to the
IBM System/3 The IBM System/3 was an IBM midrange computer introduced in 1969, and marketed until 1985. It was produced by IBM Rochester in Minnesota as a low-end business computer aimed at smaller organizations that still used IBM 1400 series computers or u ...
. (The idea of a major breakthrough with FS technology was dropped in the mid-1970s for cost-effectiveness and continuity reasons.) Later compatible IBM systems include the 4300 family, the 308x family, the 3090, the
ES/9000 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) ...
and 9672 families (
System/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 ...
family), and the
IBM Z IBM Z is a family name used by IBM for all of its z/Architecture mainframe computers. In July 2017, with another generation of products, the official family was changed to IBM Z from IBM z Systems; the IBM Z family now includes the newest mod ...
series. Computers that were mostly identical or compatible in terms of the machine code or architecture of the System/360 included
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's 470 family (and its successors),
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mainframes, the
UNIVAC 9000 series The UNIVAC 9000 series (9200, 9300, 9400, 9700) is a discontinued line of computers introduced by Sperry Rand in the mid-1960s to compete with the low end of the IBM System/360 series. The 9200 and 9300 (which differ only in CPU speed) implement ...
, Fujitsu as the Facom, the
RCA The RCA Corporation was a major American electronics company, which was founded as the Radio Corporation of America in 1919. It was initially a patent trust owned by General Electric (GE), Westinghouse, AT&T Corporation and United Fruit Comp ...
Spectra 70 The RCA Spectra 70 was a line of electronic data processing (EDP) equipment manufactured by the RCA, Radio Corporation of America’s computer division beginning in April 1965. The Spectra 70 line included several CPU models, various configuratio ...
series,The RCA Spectra 70 had radically different architecture for interrupts and I/O. There were compatibility packages to allow operating systems for System/360 to run on a Spectra/70 and vice versa. and the
English Electric System 4 The English Electric (later ICL) System 4 was a mainframe computer announced in 1965. It was derived from the RCA Spectra 70 range, itself a variant of the IBM System 360 The IBM System/360 (S/360) is a family of mainframe computer syst ...
.Intended for real-time processing, the English Electric System 4 employed four processor states, each with its own set of general purpose registers. Instructions available in the user state were identical to the System 360. The other states were entered according to the class or severity of interrupt. The fourth (the highest) state was entered when power failure was imminent, and enabled the processor to shut itself down in an orderly fashion. The System 4 machines were built under license to RCA. RCA sold the Spectra series to what was then
UNIVAC UNIVAC (Universal Automatic Computer) was a line of electronic digital stored-program computers starting with the products of the Eckert–Mauchly Computer Corporation. Later the name was applied to a division of the Remington Rand company an ...
, where they became the UNIVAC Series 70. UNIVAC also developed the
UNIVAC Series 90 The Univac 90/60 system front panel The Univac Series 90 is an obsolete family of mainframe class computer systems from UNIVAC first introduced in 1973. The low end family members included the 90/25, 90/30 and 90/40 that ran the OS/3 operating s ...
as successors to the 9000 series and Series 70. The
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produced a System/360 clone named the
ES EVM The ES EVM (russian: Единая система электронных вычислительных машин (ЕС ЭВМ), translit=Yedinaya sistema electronnykh vytchislitel'nykh mashin (ES EVM), "Unified System of Electronic Computers"), o ...
. The
IBM 5100 The IBM 5100 Portable Computer is a portable computer (one of the first) introduced in September 1975, six years before the IBM Personal Computer, and eight before the first successful IBM compatible portable computer, the Compaq Portable. It ...
portable computer, introduced in 1975, offered an option to execute the System/360's APL.SV programming language through a hardware emulator. IBM used this approach to avoid the costs and delay of creating a 5100-specific version of APL. Special
radiation-hardened Radiation hardening is the process of making electronic components and circuits resistant to damage or malfunction caused by high levels of ionizing radiation ( particle radiation and high-energy electromagnetic radiation), especially for environ ...
and otherwise somewhat modified System/360s, in the form of the System/4 Pi
avionics Avionics (a blend word, blend of ''aviation'' and ''electronics'') are the Electronics, electronic systems used on aircraft. Avionic systems include communications, Air navigation, navigation, the display and management of multiple systems, ...
computer, are used in several fighter and bomber jet aircraft. In the complete 32-bit AP-101 version, 4 Pi machines were used as the replicated computing nodes of the
fault-tolerant 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 ...
Space Shuttle The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program na ...
computer system (in five nodes). The U.S.
Federal Aviation Administration The Federal Aviation Administration (FAA) is the largest transportation agency of the U.S. government and regulates all aspects of civil aviation in the country as well as over surrounding international waters. Its powers include air traffic m ...
operated the
IBM 9020 The IBM 9020 was an IBM System/360 computer adapted into a multiprocessor system for use by the U.S. FAA for Air Traffic Control. Systems were installed in the FAA's 20 ''en route'' Air Route Traffic Control Centers (ARTCCs), beginning in the la ...
, a special cluster of modified System/360s for air traffic control, from 1970 until the 1990s. (Some 9020 software is apparently still used via
emulation Emulation may refer to: *Emulation (computing), imitation of behavior of a computer or other electronic system with the help of another type of system :*Video game console emulator, software which emulates video game consoles *Gaussian process em ...
on newer hardware.)


Table of System/360 models

: Model summary :* Six of the twenty IBM System/360 models announced either were never shipped or were never released. :* Fourteen of the twenty IBM System/360 models announced shipped.


Technical description


Influential features

The System/360 introduced a number of industry standards to the marketplace, such as: * The
8-bit In computer architecture, 8-bit Integer (computer science), integers or other Data (computing), data units are those that are 8 bits wide (1 octet (computing), octet). Also, 8-bit central processing unit (CPU) and arithmetic logic unit (ALU) arc ...
byte 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 ...
(against financial pressure during development to reduce the byte to 4 or 6 bits), rather than adopting the 7030 concept of accessing bytes of variable size at arbitrary bit addresses. * Byte- addressable memory (as opposed to bit-addressable or word-addressable memory) *
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 calculation ...
words 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 consen ...
* The
Bus and Tag Bus and Tag is an "IBM standard for a computer peripheral interface", and was commonly used to connect their mainframe computers to peripheral devices such as line printers, disk storage, magnetic tape drives and IBM 3270 display controllers. ...
I/O channel standardized in FIPS-60 * Commercial use 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 laye ...
d CPUs * The IBM Floating Point Architecture * The
EBCDIC Extended Binary Coded Decimal Interchange Code (EBCDIC; ) is an eight-bit character encoding used mainly on IBM mainframe and IBM midrange computer operating systems. It descended from the code used with punched cards and the corresponding six- ...
character setIn System/360 architecture bit 12 of the
program status word The program status word (PSW) is a register that performs the function of a status register and program counter, and sometimes more. The term is also applied to a copy of the PSW in storage. This article only discusses the PSW in the IBM System/3 ...
(PSW) controlled selection between the
EBCDIC Extended Binary Coded Decimal Interchange Code (EBCDIC; ) is an eight-bit character encoding used mainly on IBM mainframe and IBM midrange computer operating systems. It descended from the code used with punched cards and the corresponding six- ...
or a then proposed ASCII-8 mode signed decimal data. The proposed ASCII-8
ANSI The American National Standards Institute (ANSI ) is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organi ...
standard was in the approval process when System/360 was announced but it was subsequently rejected and no ASCII peripheral devices were made available. This capability was not included in System/370; bit 12 of the PSW was redefined to switch between System/360 (BC mode) and System/370 (EC mode) PSW format.
* Nine-track magnetic tape


Architectural overview

The System/360 series has a computer system architecture specification. This specification makes no assumptions on the implementation itself, but rather describes the interfaces and expected behavior of an implementation. The architecture describes mandatory interfaces that must be available on all implementations, and optional interfaces. Some aspects of this architecture are: *
Big endian In computing, endianness, also known as byte sex, is the order or sequence of bytes of a word of digital data in computer memory. Endianness is primarily expressed as big-endian (BE) or little-endian (LE). A big-endian system stores the most sig ...
byte ordering * A processor with: ** 16
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 calculation ...
general purpose 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 (R0–R15) ** A 64-bit
program status word The program status word (PSW) is a register that performs the function of a status register and program counter, and sometimes more. The term is also applied to a copy of the PSW in storage. This article only discusses the PSW in the IBM System/3 ...
(PSW), which describes (among other things) ***
Interrupt In digital computers, an interrupt (sometimes referred to as a trap) is a request for the processor to ''interrupt'' currently executing code (when permitted), so that the event can be processed in a timely manner. If the request is accepted, ...
masks *** Privilege states *** A condition code *** A 24-bit instruction address ** An interruption mechanism, maskable and unmaskable interruption classes and subclasses ** An
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 ' ...
. Each instruction is wholly described and also defines the conditions under which an exception is recognized in the form of program interruption. * A memory (called storage) subsystem with: ** 8 bits per byte ** A special processor communication area starting at address 0 ** 24-bit addressing * Manual control operations that allow ** A bootstrap process (a process called Initial Program Load or IPL) ** Operator-initiated interrupts ** Resetting the system ** Basic debugging facilities ** Manual display and modifications of the system's state (memory and processor) * An Input/Output mechanism which does not describe the devices themselves Some of the optional features are: *
Binary-coded decimal In computing and electronic systems, binary-coded decimal (BCD) is a class of binary encodings of decimal numbers where each digit is represented by a fixed number of bits, usually four or eight. Sometimes, special bit patterns are used for ...
instructions *
Floating-point 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 b ...
instructions * Timing facilities (interval timer) * Key-controlled memory protection All models of System/360, except for the Model 20 and Model 44, implemented that specification. Binary arithmetic and logical operations are performed as register-to-register and as memory-to-register/register-to-memory as a standard feature. If the Commercial Instruction Set option was installed,
packed decimal In computing and electronic systems, binary-coded decimal (BCD) is a class of binary encodings of decimal numbers where each digit is represented by a fixed number of bits, usually four or eight. Sometimes, special bit patterns are used fo ...
arithmetic could be performed as memory-to-memory with some memory-to-register operations. The Scientific Instruction Set feature, if installed, provided access to four
floating-point 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 b ...
registers that could be programmed for either
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 calculation ...
or
64-bit In computer architecture, 64-bit Integer (computer science), integers, memory addresses, or other Data (computing), data units are those that are 64 bits wide. Also, 64-bit central processing unit, CPUs and arithmetic logic unit, ALUs are those ...
floating-point operations. The Models 85 and 195 could also operate on 128-bit extended-precision floating-point numbers stored in pairs of floating-point registers, and software provided emulation in other models. The System/360 used an 8-bit byte, 32-bit word, 64-bit double-word, and 4-bit
nibble In computing, a nibble (occasionally nybble, nyble, or nybl to match the spelling of byte) is a four-bit aggregation, or half an octet. It is also known as half-byte or tetrade. In a networking or telecommunication context, the nibble is oft ...
. Machine instructions had operators with operands, which could contain register numbers or memory addresses. This complex combination of instruction options resulted in a variety of instruction lengths and formats. Memory addressing was accomplished using a base-plus-displacement scheme, with registers 1 through F (15). A displacement was encoded in 12 bits, thus allowing a 4096-byte displacement (0–4095), as the offset from the address put in a base register. Register 0 could not be used as a base register nor as an index register (nor as a branch address register), as "0" was reserved to indicate an address in the first 4 KB of memory, that is, if register 0 was specified as described, the value 0x00000000 was implicitly input to the effective address calculation in place of whatever value might be contained within register 0 (or if specified as a branch address register, then no branch was taken, and the content of register 0 was ignored, but any side effect of the instruction was performed). This specific behavior permitted initial execution of an interrupt routines, since base registers would not necessarily be set to 0 during the first few instruction cycles of an interrupt routine. It isn't needed for
IPL The Indian Premier League (IPL), also known as TATA IPL for sponsorship reasons, is a men's T20 franchise cricket league of India. It is annually contested by ten teams based out of seven Indian cities and three Indian states. The leagu ...
("Initial Program Load" or boot), as one can always clear a register without the need to save it. With the exception of the Model 67, all addresses were real memory addresses. Virtual memory was not available in most IBM mainframes until the
System/370 The IBM System/370 (S/370) is a model range of IBM mainframe computers announced on June 30, 1970, as the successors to the System/360 family. The series mostly maintains backward compatibility with the S/360, allowing an easy migration path f ...
series. The Model 67 introduced a virtual memory architecture, which MTS,
CP-67 CP-67 was the ''control program'' portion of CP/CMS, a virtual machine operating system developed for the IBM System/360-67 by IBM's Cambridge Scientific Center. It was a reimplementation of their earlier research system CP-40, which ran on a on ...
, and
TSS/360 The IBM Time Sharing System TSS/360 is a discontinued early time-sharing operating system designed exclusively for a special model of the System/360 line of mainframes, the Model 67. Made available on a trial basis to a limited set of custom ...
used—but not IBM's mainline System/360 operating systems. The System/360 machine-code instructions are 2 bytes long (no memory operands), 4 bytes long (one operand), or 6 bytes long (two operands). Instructions are always situated on 2-byte boundaries. Operations like MVC (Move-Characters) (Hex: D2) can only move at most 256 bytes of information. Moving more than 256 bytes of data required multiple MVC operations. (The
System/370 The IBM System/370 (S/370) is a model range of IBM mainframe computers announced on June 30, 1970, as the successors to the System/360 family. The series mostly maintains backward compatibility with the S/360, allowing an easy migration path f ...
series introduced a family of more powerful instructions such as the MVCL "Move-Characters-Long" instruction, which supports moving up to 16 MB as a single block.) An operand is two bytes long, typically representing an address as a 4-bit
nibble In computing, a nibble (occasionally nybble, nyble, or nybl to match the spelling of byte) is a four-bit aggregation, or half an octet. It is also known as half-byte or tetrade. In a networking or telecommunication context, the nibble is oft ...
denoting a base register and a 12-bit displacement relative to the contents of that register, in the range (shown here as
hexadecimal In mathematics and computing, the hexadecimal (also base-16 or simply hex) numeral system is a positional numeral system that represents numbers using a radix (base) of 16. Unlike the decimal system representing numbers using 10 symbols, hexa ...
numbers). The address corresponding to that operand is the contents of the specified general-purpose register plus the displacement. For example, an MVC instruction that moves 256 bytes (with length code 255 in hexadecimal as ) from base register 7, plus displacement , to base register 8, plus displacement , would be coded as the 6-byte instruction "" (operator/length/address1/address2). The System/360 was designed to separate the ''system state'' from the ''problem state''. This provided a basic level of security and recoverability from programming errors. Problem (user) programs could not modify data or program storage associated with the system state. Addressing, data, or operation exception errors made the machine enter the system state through a controlled routine so the operating system could try to correct or terminate the program in error. Similarly, it could recover certain processor hardware errors through the ''machine check'' routines.


Channels

Peripherals interfaced to the system via ''channels''. A channel is a specialized processor with the instruction set optimized for transferring data between a peripheral and main memory. In modern terms, this could be compared to
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 t ...
(DMA). The S/360 connects channels to control units with
bus and tag Bus and Tag is an "IBM standard for a computer peripheral interface", and was commonly used to connect their mainframe computers to peripheral devices such as line printers, disk storage, magnetic tape drives and IBM 3270 display controllers. ...
cables; IBM eventually replaced these with (Enterprise Systems Connection (ESCON) and Fibre Connection (FICON) channels.


Byte-multiplexor and selector channels

There were initially two types of channels; byte-multiplexer channels (known at the time simply as "multiplexor channels"), for connecting "slow speed" devices such as card readers and punches,
line printer A line printer prints one entire line of text before advancing to another line. Most early line printers were impact printers. Line printers are mostly associated with unit record equipment and the early days of digital computing, but the ...
s, and communications controllers, and selector channels for connecting high speed devices, such as
disk drive Disk storage (also sometimes called drive storage) is a general category of storage mechanisms where data is recorded by various electronic, magnetic, optical, or mechanical changes to a surface layer of one or more rotating disks. A disk drive is ...
s,
tape drive A tape drive is a data storage device that reads and writes data on a magnetic tape. Magnetic tape data storage is typically used for offline, archival data storage. Tape media generally has a favorable unit cost and a long archival stability. ...
s, data cells and
drums A drum kit (also called a drum set, trap set, or simply drums) is a collection of drums, cymbals, and other Percussion instrument, auxiliary percussion instruments set up to be played by one person. The player (drummer) typically holds a pair o ...
. Every System/360 (except for the Model 20, which was not a standard 360) has a byte-multiplexer channel and 1 or more selector channels, though the model 25 has just one channel, which can be either a byte-multiplexor or selector channel. The smaller models (up to the model 50) have integrated channels, while for the larger models (model 65 and above) the channels are large separate units in separate cabinets: the IBM 2870 is the byte-multiplexor channel with up to four selector sub-channels, and the IBM 2860 is up to three selector channels. The byte-multiplexer channel is able to handle I/O to/from several devices simultaneously at the device's highest rated speeds, hence the name, as it
multiplexed In telecommunications and computer networking, multiplexing (sometimes contracted to muxing) is a method by which multiple analog or digital signals are combined into one signal over a shared medium. The aim is to share a scarce resource - a ...
I/O from those devices onto a single data path to main memory. Devices connected to a byte-multiplexer channel are configured to operate in 1-byte, 2-byte, 4-byte, or "burst" mode. The larger "blocks" of data are used to handle progressively faster devices. For example, a 2501 card reader operating at 600 cards per minute would be in 1-byte mode, while a 1403-N1 printer would be in burst mode. Also, the byte-multiplexer channels on larger models have an optional selector subchannel section that would accommodate tape drives. The byte-multiplexor's channel address was typically "0" and the selector subchannel addresses were from "C0" to "FF." Thus, tape drives on System/360 were commonly addressed at 0C0–0C7. Other common byte-multiplexer addresses are: 00A: 2501 Card Reader, 00C/00D: 2540 Reader/Punch, 00E/00F: 1403-N1 Printers, 010–013: 3211 Printers, 020–0BF: 2701/2703 Telecommunications Units. These addresses are still commonly used in z/VM virtual machines. System/360 models 40 and 50 have an integrated 1052-7 console that is usually addressed as 01F, however, this was not connected to the byte-multiplexer channel, but rather, had a direct internal connection to the mainframe. The model 30 attached a different model of 1052 through a 1051 control unit. The models 60 through 75 also use the 1052-7. Selector channels enabled I/O to high speed devices. These storage devices were attached to a control unit and then to the channel. The control unit let clusters of devices be attached to the channels. On higher speed models, multiple selector channels, which could operate simultaneously or in parallel, improved overall performance. Control units are connected to the channels with "bus and tag" cable pairs. The bus cables carried the address and data information and the tag cables identified what data was on the bus. The general configuration of a channel is to connect the devices in a chain, like this: Mainframe—Control Unit X—Control Unit Y—Control Unit Z. Each control unit is assigned a "capture range" of addresses that it services. For example, control unit X might capture addresses 40–4F, control unit Y: C0–DF, and control unit Z: 80–9F. Capture ranges had to be a multiple of 8, 16, 32, 64, or 128 devices and be aligned on appropriate boundaries. Each control unit in turn has one or more devices attached to it. For example, you could have control unit Y with 6 disks, that would be addressed as C0-C5. There are three general types of bus-and-tag cables produced by IBM. The first is the standard gray bus-and-tag cable, followed by the blue bus-and-tag cable, and finally the tan bus-and-tag cable. Generally, newer cable revisions are capable of higher speeds or longer distances, and some peripherals specified minimum cable revisions both upstream and downstream. The cable ordering of the control units on the channel is also significant. Each control unit is "strapped" as High or Low priority. When a device selection was sent out on a mainframe's channel, the selection was sent from X->Y->Z->Y->X. If the control unit was "high" then the selection was checked in the outbound direction, if "low" then the inbound direction. Thus, control unit X was either 1st or 5th, Y was either 2nd or 4th, and Z was 3rd in line. It is also possible to have multiple channels attached to a control unit from the same or multiple mainframes, thus providing a rich high-performance, multiple-access, and backup capability. Typically the total cable length of a channel is limited to 200 feet, less being preferred. Each control unit accounts for about 10 "feet" of the 200-foot limit.


Block multiplexer channel

IBM first introduced a new type of I/O channel on the Model 85 and Model 195, the 2880 block multiplexer channel, and then made them standard on the
System/370 The IBM System/370 (S/370) is a model range of IBM mainframe computers announced on June 30, 1970, as the successors to the System/360 family. The series mostly maintains backward compatibility with the S/360, allowing an easy migration path f ...
. This channel allowed a device to suspend a channel program, pending the completion of an I/O operation and thus to free the channel for use by another device. A block multiplexer channel can support either standard 1.5 MB/second connections or, with the 2-byte interface feature, 3 MB/second; the latter use one tag cable and two bus cables. On the
S/370 The IBM System/370 (S/370) is a model range of IBM mainframe computers announced on June 30, 1970, as the successors to the System/360 family. The series mostly maintains backward compatibility with the S/360, allowing an easy migration path f ...
there is an option for a 3.0 MB/s data streaming channel with one bus cable and one tag cable. The initial use for this was the 2305 fixed-head disk, which has 8 "exposures" (alias addresses) and rotational position sensing (RPS). Block multiplexer channels can operate as a selector channel to allow compatible attachment of legacy subsystems.


Basic hardware components

Being uncertain of the reliability and availability of the then new monolithic
integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...
s, IBM chose instead to design and manufacture its own custom
hybrid integrated circuit A hybrid integrated circuit (HIC), hybrid microcircuit, hybrid circuit or simply hybrid is a miniaturized electronic circuit constructed of individual devices, such as semiconductor devices (e.g. transistors, diodes or monolithic ICs) and pa ...
s. These were built on 11 mm square
ceramic A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain ...
substrates.
Resistor A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active el ...
s were silk screened on and discrete
glass Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenching) of ...
encapsulated
transistor upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink). A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch e ...
s and
diode A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other. A diode ...
s were added. The substrate was then covered with a metal lid or encapsulated in plastic to create a "
Solid Logic Technology Solid Logic Technology (SLT) was IBM's method for hybrid packaging of electronic circuitry introduced in 1964 with the IBM System/360 series of computers and related machines. IBM chose to design custom hybrid circuits using discrete, flip chi ...
" (SLT) module. A number of thes
SLT modules
were then
flip chip Flip chip, also known as controlled collapse chip connection or its abbreviation, C4, is a method for interconnecting dies such as semiconductor devices, IC chips, integrated passive devices and microelectromechanical systems (MEMS), to externa ...
mounted onto a small multi-layer
printed circuit A printed circuit board (PCB; also printed wiring board or PWB) is a medium used in electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a laminated sandwich struc ...
"SLT card". Each card had one or two sockets on one edge that plugged onto pins on one of the computer's "SLT boards". This was the reverse of how most other company's cards were mounted, where the cards had pins or printed contact areas and plugged into sockets on the computer's boards. Up to twenty SLT boards could be assembled side-by-side (vertically and horizontally) to form a "logic gate". Several gates mounted together constituted a box-shaped "logic frame". The outer gates were generally hinged along one vertical edge so they could be swung open to provide access to the fixed inner gates. The larger machines could have more than one frame bolted together to produce the final unit, such as a multi-frame Central Processing Unit (CPU).


Operating system software

The smaller System/360 models used the Basic Operating System/360 (
BOS/360 Basic Operating System/360 (BOS/360) was an early IBM System/360 operating system. Origin BOS was one of four System/360 Operating System versions developed by the IBM General Products Division (GPD) in Endicott, New York to fill a gap at th ...
), Tape Operating System (TOS/360), or Disk Operating System/360 ( DOS/360, which evolved into DOS/VS, DOS/VSE, VSE/AF, VSE/SP, VSE/ESA, and then
z/VSE VSEn (''Virtual Storage Extended'') is an operating system for IBM mainframe computers, the latest one in the DOS/360 lineage, which originated in 1965. DOS/VSE was introduced in 1979 as a successor to DOS/VS; in turn, DOS/VSE was succeeded by ...
). The larger models used Operating System/360 (OS/360). IBM developed several levels of OS/360, with increasingly powerful features: Primary Control Program (PCP),
Multiprogramming with a Fixed number of Tasks OS/360, officially known as IBM System/360 Operating System, is a discontinued batch processing operating system developed by IBM for their then-new System/360 mainframe computer, announced in 1964; it was influenced by the earlier IBSYS/IBJ ...
(MFT), and
Multiprogramming with a Variable number of Tasks OS/360, officially known as IBM System/360 Operating System, is a discontinued batch processing operating system developed by IBM for their then-new System/360 mainframe computer, announced in 1964; it was influenced by the earlier IBM 7090/94 I ...
(MVT). MVT took a long time to develop into a usable system, and the less ambitious MFT was widely used. PCP was used on intermediate machines too small to run MFT well, and on larger machines before MFT was available; the final releases of OS/360 included only MFT and MVT. For the
System/370 The IBM System/370 (S/370) is a model range of IBM mainframe computers announced on June 30, 1970, as the successors to the System/360 family. The series mostly maintains backward compatibility with the S/360, allowing an easy migration path f ...
and later machines, MFT evolved into
OS/VS1 Operating System/Virtual Storage 1, or OS/VS1, is a discontinued IBM mainframe computer operating system designed to be run on IBM System/370 hardware. It was the successor to the OS/360 and successors#MFT, Multiprogramming with a Fixed number of ...
, while MVT evolved into
OS/VS2 (SVS) Single Virtual Storage (SVS) refers to Release 1 of Operating System/Virtual Storage 2 (OS/VS2); it is the successor system to the MVT option of Operating System/360. OS/VS2 (SVS) was a stopgap measure pending the availability of MVS, although ...
(Single Virtual Storage), then various versions of
MVS Multiple Virtual Storage, more commonly called MVS, was the most commonly used operating system on the System/370 and System/390 IBM mainframe computers. IBM developed MVS, along with OS/VS1 and SVS, as a successor to OS/360. It is unrelated ...
(Multiple Virtual Storage) culminating in the current
z/OS z/OS is a 64-bit operating system for IBM z/Architecture mainframes, introduced by IBM in October 2000. It derives from and is the successor to OS/390, which in turn was preceded by a string of MVS versions.Starting with the earliest: * O ...
. When it announced the Model 67 in August 1965, IBM also announced
TSS/360 The IBM Time Sharing System TSS/360 is a discontinued early time-sharing operating system designed exclusively for a special model of the System/360 line of mainframes, the Model 67. Made available on a trial basis to a limited set of custom ...
(Time-Sharing System) for delivery at the same time as the 67. TSS/360, a response to
Multics Multics ("Multiplexed Information and Computing Service") is an influential early time-sharing operating system based on the concept of a single-level memory.Dennis M. Ritchie, "The Evolution of the Unix Time-sharing System", Communications of t ...
, was an ambitious project that included many advanced features. It had performance problems, was delayed, canceled, reinstated, and finally canceledHowever, it could still be ordered, and a TSS/370 PRPQ was available on the S/370 and went through multiple releases. again in 1971. Customers migrated to
CP-67 CP-67 was the ''control program'' portion of CP/CMS, a virtual machine operating system developed for the IBM System/360-67 by IBM's Cambridge Scientific Center. It was a reimplementation of their earlier research system CP-40, which ran on a on ...
, MTS (
Michigan Terminal System The Michigan Terminal System (MTS) is one of the first time-sharing computer operating systems.. Developed in 1967 at the University of Michigan for use on IBM S/360-67, S/370 and compatible mainframe computers, it was developed and used by a con ...
), TSO (
Time Sharing Option Time Sharing Option (TSO) is an interactive time-sharing environment for IBM mainframe operating systems, including OS/360 MVT, OS/VS2 (SVS), MVS, OS/390, and z/OS. Use In computing, time-sharing is a design technique that allows many peop ...
for OS/360), or one of several other
time-sharing In computing, time-sharing is the sharing of a computing resource among many users at the same time by means of multiprogramming and multi-tasking.DEC Timesharing (1965), by Peter Clark, The DEC Professional, Volume 1, Number 1 Its emergence a ...
systems. CP-67, the original
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 hardw ...
system, was also known as
CP/CMS CP/CMS (Control Program/Cambridge Monitor System) is a discontinued time-sharing operating system of the late 1960s and early 1970s, known for its excellent performance and advanced features. It had three distinct versions: * CP-40/CMS, an imp ...
. CP/67 was developed outside the IBM mainstream at IBM's
Cambridge Scientific Center The IBM Cambridge Scientific Center was a company research laboratory established in February 1964 in Cambridge, Massachusetts. Situated at 545 Technology Square (''Tech Square''), in the same building as MIT's Project MAC, it was later renamed ...
, in cooperation with
MIT The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of the m ...
researchers. CP/CMS eventually won wide acceptance, and led to the development of
VM/370 VM (often: VM/CMS) is a family of IBM virtual machine operating systems used on IBM mainframes System/370, System/390, zSeries, System z and compatible systems, including the Hercules (emulator), Hercules emulator for personal computers. The ...
(Virtual Machine) which had a primary interactive "sub" operating system known as
VM/CMS VM (often: VM/CMS) is a family of IBM virtual machine operating systems used on IBM mainframes System/370, System/390, zSeries, System z and compatible systems, including the Hercules emulator for personal computers. The following versions ...
(Conversational Monitoring System). This evolved into today's
z/VM z/VM is the current version in IBM's VM family of virtual machine operating systems. z/VM was first released in October 2000 and remains in active use and development . It is directly based on technology and concepts dating back to the 1960s, wi ...
. The Model 20 offered a simplified and rarely used tape-based system called TPS (Tape Processing System), and DPS (Disk Processing System) that provided support for the 2311 disk drive. TPS could run on a machine with 8 KB of memory; DPS required 12 KB, which was pretty hefty for a Model 20. Many customers ran quite happily with 4 KB and CPS (Card Processing System). With TPS and DPS, the card reader was used to read the
Job Control Language Job Control Language (JCL) is a name for scripting languages used on IBM mainframe operating systems to instruct the system on how to run a batch job or start a subsystem. More specifically, the purpose of JCL is to say which programs to run, ...
cards that defined the stack of jobs to run and to read in transaction data such as customer payments. The operating system was held on tape or disk, and results could also be stored on the tapes or hard drives. Stacked job processing became an exciting possibility for the small but adventurous computer user. A little-known and little-used suite of 80-column punched-card utility programs known as Basic Programming Support (BPS) (jocularly: Barely Programming Support), a precursor of TOS, was available for smaller systems.


Component names

IBM created a new naming system for the new components created for System/360, although well-known old names, like
IBM 1403 The IBM 1403 line printer was introduced as part of the IBM 1401 computer in 1959 and had an especially long life in the IBM product line. Description The original model can print 600 lines of text per minute and can skip blank lines at up to ...
and
IBM 1052 IBM 1050 Data Communications System is a computer terminal subsystem to send data to and receive data from another 1050 subsystem or IBM computer in the IBM 1400, IBM 7000 or System/360 series. It first became available in 1963 and was used wide ...
, were retained. In this new naming system, components were given four-digit numbers starting with 2. The second digit described the type of component, as follows:


Peripherals

IBM developed a new family of peripheral equipment for System/360, carrying over a few from its older 1400 series. Interfaces were standardized, allowing greater flexibility to mix and match processors, controllers and peripherals than in the earlier product lines. In addition, System/360 computers could use certain peripherals that were originally developed for earlier computers. These earlier peripherals used a different numbering system, such as the
IBM 1403 The IBM 1403 line printer was introduced as part of the IBM 1401 computer in 1959 and had an especially long life in the IBM product line. Description The original model can print 600 lines of text per minute and can skip blank lines at up to ...
chain printer. The 1403, an extremely reliable device that had already earned a reputation as a workhorse, was sold as the 1403-N1 when adapted for the System/360. Also available were
optical character recognition Optical character recognition or optical character reader (OCR) is the electronic or mechanical conversion of images of typed, handwritten or printed text into machine-encoded text, whether from a scanned document, a photo of a document, a scen ...
(OCR) readers IBM 1287 and IBM 1288 which could read Alpha Numeric (A/N) and Numeric Hand Printed (NHP/NHW) Characters from Cashier's rolls of tape to full legal size pages. At the time this was done with very large optical/logic readers. Software was too slow and expensive at that time. Models 65 and below sold with an IBM 1052-7 as the console typewriter. The 360/85 with feature 5450 uses a display console that was not compatible with anything else in the line; the later 3066 console for the 370/165 and 370/168 use the same basic display design as the 360/85. The IBM System/360 models 91 and 195 use a graphical display similar to the IBM 2250 as their primary console. Additional operator consoles were also available. Certain high-end machines could optionally be purchased with a 2250 graphical display, costing upwards of US $100,000; smaller machines could use the less expensive 2260 display or later the 3270.


Direct access storage devices (DASD)

The first disk drives for System/360 were
IBM 2302 IBM manufactured magnetic disk storage devices from 1956 to 2003, when it sold its hard disk drive business to Hitachi. Both the hard disk drive (HDD) and floppy disk drive (FDD) were invented by IBM and as such IBM's employees were responsible ...
s and
IBM 2311 IBM manufactured magnetic disk storage devices from 1956 to 2003, when it sold its hard disk drive business to Hitachi. Both the hard disk drive (HDD) and floppy disk drive (FDD) were invented by IBM and as such IBM's employees were responsible fo ...
s. The first drum for System/360 was the
IBM 7320 In addition to the drums used as main memory by IBM, e.g., IBM 305, IBM 650, IBM offered drum devices as secondary storage for the 700/7000 series and System/360 series of computers. IBM 731 The IBM 731 is a discontinued storage unit used o ...
. The 156 KB/second 2302 was based on the earlier 1302 and was available as a model 3 with two 112.79 MB modules or as a model 4 with four such modules. The 2311, with a removable 1316
disk pack Disk packs and disk cartridges were early forms of removable media for computer data storage, introduced in the 1960s. Disk pack A disk pack is a layered grouping of hard disk platters (circular, rigid discs coated with a magnetic data storage ...
, was based on the
IBM 1311 IBM manufactured magnetic disk storage devices from 1956 to 2003, when it sold its hard disk drive business to Hitachi. Both the hard disk drive (HDD) and floppy disk drive (FDD) were invented by IBM and as such IBM's employees were responsible fo ...
and had a theoretical capacity of 7.2 MB, although actual capacity varied with record design. (When used with a 360/20, the 1316 pack was formatted into fixed-length 270 byte
sectors Sector may refer to: Places * Sector, West Virginia, U.S. Geometry * Circular sector, the portion of a disc enclosed by two radii and a circular arc * Hyperbolic sector, a region enclosed by two radii and a hyperbolic arc * Spherical sector, a p ...
, giving a maximum capacity of 5.4MB.) In 1966, the first 2314s shipped. This device had up to eight usable disk drives with an integral control unit; there were nine drives, but one was reserved as a spare. Each drive used a removable 2316 disk pack with a capacity of nearly 28 MB. The disk packs for the 2311 and 2314 were ''physically'' large by today's standards — e.g., the 1316 disk pack was about in diameter and had six platters stacked on a central spindle. The top and bottom outside platters did not store data. Data were recorded on the inner sides of the top and bottom platters and both sides of the inner platters, providing 10 recording surfaces. The 10 read/write heads moved together across the surfaces of the platters, which were formatted with 203 concentric tracks. To reduce the amount of head movement (seeking), data was written in a virtual cylinder from inside top platter down to inside bottom platter. These disks were not usually formatted with fixed-sized sectors as are today's hard drives (though this ''was'' done with
CP/CMS CP/CMS (Control Program/Cambridge Monitor System) is a discontinued time-sharing operating system of the late 1960s and early 1970s, known for its excellent performance and advanced features. It had three distinct versions: * CP-40/CMS, an imp ...
). Rather, most System/360 I/O software could customize the length of the data record (variable-length records), as was the case with magnetic tapes. Some of the most powerful early System/360s used high-speed head-per-track drum storage devices. The 3,500 RPM 2301, which replaced the 7320, was part of the original System/360 announcement, with a capacity of 4 MB. The 303.8 KB/second IBM 2303 was announced on January 31, 1966, with a capacity of 3.913 MB. These were the only drums announced for System/360 and System/370, and their niche was later filled by fixed-head disks. The 6,000 RPM 2305 appeared in 1970, with capacities of 5 MB (2305-1) or 11 MB (2305-2) per module. Although these devices did not have large capacity, their speed and transfer rates made them attractive for high-performance needs. A typical use was overlay linkage (e.g. for OS and application subroutines) for program sections written to alternate in the same memory regions. Fixed head disks and drums were particularly effective as paging devices on the early virtual memory systems. The 2305, although often called a "drum" was actually a head-per-track disk device, with 12 recording surfaces and a data transfer rate up to 3 MB per second. Rarely seen was the
IBM 2321 Data Cell The IBM 2321 Data Cell announced in April 1964 (withdrawn January 1975) is a discontinued direct access storage device (DASD) for the IBM System/360. It holds up to 400 megabytes of data, with an access time of 95 milliseconds to 600 milliseconds ...
, a mechanically complex device that contained multiple magnetic strips to hold data; strips could be randomly accessed, placed upon a cylinder-shaped drum for read/write operations; then returned to an internal storage cartridge. The IBM Data Cell oodle pickerwas among several IBM trademarked "speedy" mass online direct-access storage peripherals (reincarnated in recent years as "virtual tape" and automated tape librarian peripherals). The 2321 file had a capacity of 400 MB, at the time when the 2311 disk drive only had 7.2 MB. The IBM Data Cell was proposed to fill cost/capacity/speed gap between magnetic tapes—which had high capacity with relatively low cost per stored byte—and disks, which had higher expense per byte. Some installations also found the electromechanical operation less dependable and opted for less mechanical forms of direct-access storage. The Model 44 was unique in offering an integrated single-disk drive as a standard feature. This drive used the 2315 "ramkit" cartridge and provided 1,171,200 bytes of storage.


Tape drives

The 2400-series of 1/2" magnetic tape units consisted of the 2401 and 2402 Models 1-6 Magnetic Tape Units, the 2403 Models 1-6 Magnetic Tape Unit and Control, the 2404 Models 1-3 Magnetic Tape Unit and Control, and the 2803/2804 Models 1 and 2 Tape Control Units. The later 2415 Magnetic Tape Unit and Control, introduced in 1967 contained two, four, or six tape drives and a control in a single unit, and was slower and cheaper. The 2415 drives and control were not marketed separately. With System/360, IBM switched from IBM 7-track to 9-track tape format. Some 2400-series drives could be purchased that read and wrote 7-track tapes for compatibility with the older
IBM 729 The IBM 729 Magnetic Tape Unit was IBM's iconic tape mass storage system from the late 1950s through the mid-1960s. Part of the IBM 7 track family of tape units, it was used on late 700, most 7000 and many 1400 series computers. Like its pred ...
tape drives. In 1968, the IBM 2420 tape system was released, offering much higher data rates, self-threading tape operation and 1600bpi packing density. It remained in the product line until 1979.


Unit record devices

* Punched card devices included the 2501 card reader and the 2540 card reader punch. Virtually every System/360 had a 2540. The 2560 MFCM ("Multi-Function Card Machine") reader/sorter/punch, listed above, was for the Model 20 only. It was notorious for reliability problems (earning humorous acronyms often involving "...Card Muncher" or "Mal-Function Card Machine"). *
Line printer A line printer prints one entire line of text before advancing to another line. Most early line printers were impact printers. Line printers are mostly associated with unit record equipment and the early days of digital computing, but the ...
s were the
IBM 1403 The IBM 1403 line printer was introduced as part of the IBM 1401 computer in 1959 and had an especially long life in the IBM product line. Description The original model can print 600 lines of text per minute and can skip blank lines at up to ...
and the slower
IBM 1443 The IBM 1443 Printer (sometimes referred to as the ''1443 Flying Type Bar Printer'') is an obsolete computer line printer used in the punched card era. It was offered in three models: Models 1, 2 and N1; the last two could print up to 240 lines p ...
. * A paper tape reader, the IBM 2671, was introduced in 1964. It had a rated speed of 1,000 cps. There were also a paper tape reader and paper tape punch from an earlier era, available only as RPQs (
Request Price Quotation Request price quotation or RPQ is a long-standing IBM designation for a product or component that is potentially available, but that is not on the "standard" price list. Typical RPQ offerings are custom interfaces, hardware modifications, researc ...
). The 1054 (reader) and 1055 (punch), which were carried forward (like the 1052 console typewriter) from the IBM 1050 Teleprocessing System. All these devices operated at a maximum of 15.5 characters per second. The paper tape punch from the IBM 1080 System was also available by RPQ, but at a prohibitively expensive price. *
Optical character recognition Optical character recognition or optical character reader (OCR) is the electronic or mechanical conversion of images of typed, handwritten or printed text into machine-encoded text, whether from a scanned document, a photo of a document, a scen ...
(OCR) devices 1287 and later the 1288 were available on the 360's. The 1287 could read handwritten numerals, some OCR fonts, and cash register OCR paper tape reels. The 1288 'page reader' could handle up to legal size OCR font typewritten pages, as well as handwritten numerals. Both of these OCR devices employed a 'flying spot' scanning principle, with the raster scan provided by a large CRT, and the reflected light density changes were picked up by a high gain
photomultiplier A photomultiplier is a device that converts incident photons into an electrical signal. Kinds of photomultiplier include: * Photomultiplier tube, a vacuum tube converting incident photons into an electric signal. Photomultiplier tubes (PMTs for sho ...
tube. *
Magnetic ink character recognition Magnetic ink character recognition code, known in short as MICR code, is a character recognition technology used mainly by the banking industry to streamline the processing and clearance of cheques and other documents. MICR encoding, called the ' ...
(MICR) was provided by the IBM 1412 and 1419 cheque sorters, with magnetic ink printing (for cheque books) on 1445 printers (a modified 1443 that used an MICR ribbon). 1412/1419 and 1445 were mainly used by banking institutions.


Remaining machines

Despite having been sold or leased in very large numbers for a mainframe system of its era, only a few of System/360 computers remain—mainly as non-operating property of museums or collectors. Examples of existing systems include: * The
Computer History Museum The Computer History Museum (CHM) is a museum of computer history, located in Mountain View, California. The museum presents stories and artifacts of Silicon Valley and the information age, and explores the computing revolution and its impact on ...
in
Mountain View, California Mountain View is a city in Santa Clara County, California, United States. Named for its views of the Santa Cruz Mountains, it has a population of 82,376. Mountain View was integral to the early history and growth of Silicon Valley, and is the ...
, has a non-working Model 30 on display, as do the
Museum of Transport and Technology The Museum of Transport and Technology (MOTAT) is a science and technology museum located in Western Springs, Auckland, New Zealand. It is located close to the Western Springs Stadium, Auckland Zoo and the Western Springs Park. The museum has l ...
in
Auckland Auckland (pronounced ) ( mi, Tāmaki Makaurau) is a large metropolitan city in the North Island of New Zealand. The List of New Zealand urban areas by population, most populous urban area in the country and the List of cities in Oceania by po ...
, New Zealand, and the
Vienna University of Technology TU Wien (TUW; german: Technische Universität Wien; still known in English as the Vienna University of Technology from 1975–2014) is one of the major universities in Vienna, Austria. The university finds high international and domestic recogn ...
in Austria. * The
University of Western Australia The University of Western Australia (UWA) is a public research university in the Australian state of Western Australia. The university's main campus is in Perth, the state capital, with a secondary campus in Albany, Western Australia, Albany an ...
Computer Club has a complete Model 40 in storage. * The KCG Computer Museum of Kyoto Computer Gakuin, Japan's first computer school in town, has an IBM System/360 Model 40 on display.Large and Midsized Computers at KCG Computer Museum
(in Japanese) an

/ref> * Two
IBM System/360 Model 20 The IBM System/360 Model 20 is the smallest member of the IBM System/360 family announced in November 1964. The Model 20 supports only a subset of the System/360 instruction set, with binary numbers limited to 16 bits and no floating point. In ...
processors along with numerous peripherals (forming two complete systems) located in
Nuremberg, Germany Nuremberg ( ; german: link=no, Nürnberg ; in the local East Franconian dialect: ''Nämberch'' ) is the second-largest city of the German state of Bavaria after its capital Munich, and its 518,370 (2019) inhabitants make it the 14th-largest ci ...
, were purchased on
eBay eBay Inc. ( ) is an American multinational e-commerce company based in San Jose, California, that facilitates consumer-to-consumer and business-to-consumer sales through its website. eBay was founded by Pierre Omidyar in 1995 and became a ...
in April/May 2019 for €3,710 by two UK enthusiasts, Adam Bradley and Chris Blackburn, who, over the course of some months, moved the machine to
Creslow Park Creslow Park is a large specialist technical facility located in Creslow, in the Aylesbury Vale in the English county of Buckinghamshire. It was originally established in 1944 as Creslow Transmission Station, a top secret radio communications facili ...
in
Buckinghamshire Buckinghamshire (), abbreviated Bucks, is a ceremonial county in South East England that borders Greater London to the south-east, Berkshire to the south, Oxfordshire to the west, Northamptonshire to the north, Bedfordshire to the north-ea ...
, United Kingdom. The system was in a small, abandoned building left untouched for decades, and apparently had been used in that building since all peripherals were still fully wired and interconnected. The systems are now in a dedicated machine room, and are undergoing restoration in preparation for public display in the future. * The Living Computers: Museum + Labs has a 360 model 30. A running list of remaining System/360s that are more than just 'front panels' can be found a
World Inventory of remaining System/360 CPUs


Gallery

This gallery shows the operator's
console Console may refer to: Computing and video games * System console, a physical device to operate a computer ** Virtual console, a user interface for multiple computer consoles on one device ** Command-line interface, a method of interacting with ...
, with register value lamps,
toggle switch In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...
es (middle of pictures), and " emergency pull" switch (upper right of pictures) of the various models. File:IBM System 360-30 front panel.agr.jpg, Model 30 File:Museum of Science, Boston, MA - IMG 3166.JPG, Model 40 File:IBM 360-44.5.jpg, Model 44 File:IBM system 360-50 console - MfK Bern.jpg, Model 50 File:Console, IBM System 360 Model 65.jpg, Model 65 File:IBM360-67AtUmichWithMikeAlexander.jpg, Model 67 File:Supercomputer NSA-IBM360 85.jpg, Model 85 File:IBM System 36091.sj.jpg, Model 91


See also

*
History of IBM International Business Machines (IBM), nicknamed "Big Blue", is a multinational computer technology and IT consulting corporation headquartered in Armonk, New York, United States. IBM originated from the unification of several companies that wo ...
*
List of IBM products The following is a partial list of products, services, and subsidiaries of International Business Machines (IBM) Corporation and its predecessor corporations, beginning in the 1890s. This list is eclectic; it includes, for example, the ''AN/FS ...
*
IBM System/4 Pi The IBM System/4 Pi is a family of avionics computers used, in various versions, on the F-15 Eagle fighter, E-3 Sentry AWACS, Harpoon Missile, NASA's Skylab, MOL, and the Space Shuttle, as well as other aircraft. Development began in 1965, de ...
*
Gerrit Blaauw Gerrit Anne "Gerry" Blaauw (July 17, 1924 – March 21, 2018) was a Dutch computer scientist, known as one of the principal designers of the IBM System/360 line of computers, together with Fred Brooks, Gene Amdahl, and others. ...
* Bob O. Evans


Notes


References


External links

*
IBM System/360 System Summary 11th edition August 1969




* ttp://www.beagle-ears.com/lars/engineer/comphist/ibm360.htm Generations of the IBM 360/370/3090/390by Lars Poulsen with multiple links and references
Description of a large IBM System/360 model 75 installation at JPL

"The Beginning of I.T. Civilization - IBM's System/360 Mainframe" by Mike Kahn

Illustrations from “Introduction to IBM Data Processing Systems”, 1968
contains photographs of IBM System/360 computers and peripherals
IBM System 360 RPG Debugging Template and Keypunch Card

Video of a two-hour lecture and panel discussion
entitled ''The IBM System/360 Revolution'', from the
Computer History Museum The Computer History Museum (CHM) is a museum of computer history, located in Mountain View, California. The museum presents stories and artifacts of Silicon Valley and the information age, and explores the computing revolution and its impact on ...
on 2004-04-07
Original vintage film from 1964
IBM System/360 Computer History Archives Project

of a dual processor IBM 360/67 at the
University of Michigan , mottoeng = "Arts, Knowledge, Truth" , former_names = Catholepistemiad, or University of Michigania (1817–1821) , budget = $10.3 billion (2021) , endowment = $17 billion (2021)As o ...
's academic Computing Center in the late 1960s or early 1970s are included in Dave Mills' article describing the
Michigan Terminal System The Michigan Terminal System (MTS) is one of the first time-sharing computer operating systems.. Developed in 1967 at the University of Michigan for use on IBM S/360-67, S/370 and compatible mainframe computers, it was developed and used by a con ...
(MTS)
Pictures
of an
IBM System/360 Model 67 The IBM System/360 Model 67 (S/360-67) was an important IBM mainframe model in the late 1960s. * It had "its own powerful operating system... heTime Sharing System monitor (TSS)" offering "virtually instantaneous access to and response from t ...
at Newcastle (UK) University * * *


From the ''IBM Journal of Research and Development''

* *


From ''IBM Systems Journal''

* * * * * * {{DEFAULTSORT:Ibm System 360 Computing platforms 1960s software Computer-related introductions in 1964 Instruction set architectures 32-bit computers