IBM mainframes are large computer systems produced by
IBM
International Business Machines Corporation (using the trademark IBM), nicknamed Big Blue, is an American Multinational corporation, multinational technology company headquartered in Armonk, New York, and present in over 175 countries. It is ...
since 1952. During the 1960s and 1970s, IBM dominated the computer market with the
7000 series and the later
System/360
The IBM System/360 (S/360) is a family of mainframe computer systems announced by IBM on April 7, 1964, and delivered between 1965 and 1978. System/360 was the first family of computers designed to cover both commercial and scientific applicati ...
, followed by the
System/370
The IBM System/370 (S/370) is a range of IBM mainframe computers announced as the successors to the IBM System/360, System/360 family on June 30, 1970. The series mostly maintains backward compatibility with the S/360, allowing an easy migrati ...
. Current
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, enterprise ...
s in IBM's line of business computers are developments of the basic design of the System/360.
First and second generation

From 1952 into the late 1960s, IBM manufactured and marketed several large computer models, known as the
IBM 700/7000 series
The IBM 700/7000 series is a series of large-scale (Mainframe computer, mainframe) computer systems that were made by IBM through the 1950s and early 1960s. The series includes several different, incompatible processor architectures. The 700s ...
. The
first-generation 700s were based on
vacuum tube
A vacuum tube, electron tube, thermionic valve (British usage), or tube (North America) is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied. It ...
s, while the later, second-generation 7000s used
transistor
A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch electrical signals and electric power, power. It is one of the basic building blocks of modern electronics. It is composed of semicondu ...
s. These machines established IBM's dominance in
electronic data processing
Electronic data processing (EDP) or business information processing can refer to the use of automated methods to process commercial data. Typically, this uses relatively simple, repetitive activities to process large volumes of similar information ...
("EDP"). IBM had two model categories: one (701, 704, 709, 7030, 7090, 7094, 7040, 7044) for engineering and scientific use, and one (702, 705, 705-II, 705-III, 7080, 7070, 7072, 7074, 7010) for commercial or data processing use. The two categories, scientific and commercial, generally used common peripherals but had completely different
instruction set
In computer science, an instruction set architecture (ISA) is an abstract model that generally defines how software controls the CPU in a computer or a family of computers. A device or program that executes instructions described by that ISA, s ...
s, and there were incompatibilities even within each category.
IBM initially sold its computers without any software, expecting customers to write their own; programs were manually initiated, one at a time. Later, IBM provided
compilers
In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs tha ...
for the newly developed higher-level
programming language
A programming language is a system of notation for writing computer programs.
Programming languages are described in terms of their Syntax (programming languages), syntax (form) and semantics (computer science), semantics (meaning), usually def ...
s
Fortran,
COMTRAN
COMTRAN (COMmercial TRANslator) is an early programming language developed at IBM. It was intended as the business programming equivalent of the scientific programming language FORTRAN (FORmula TRANslator). It served as one of the forerunners ...
and later
COBOL
COBOL (; an acronym for "common business-oriented language") is a compiled English-like computer programming language designed for business use. It is an imperative, procedural, and, since 2002, object-oriented language. COBOL is primarily ...
. The first
operating systems
An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs.
Time-sharing operating systems scheduler (computing), schedule tasks for ...
for IBM computers were written by IBM customers who did not wish to have their very expensive machines (US$2M in the mid-1950s) sitting idle while operators set up jobs manually. These first operating systems were essentially scheduled work queues. It is generally thought the first operating system used for real work was
GM-NAA I/O, produced by
General Motors
General Motors Company (GM) is an American Multinational corporation, multinational Automotive industry, automotive manufacturing company headquartered in Detroit, Michigan, United States. The company is most known for owning and manufacturing f ...
' Research division in 1956. IBM enhanced one of GM-NAA I/O's successors, the
SHARE Operating System, and provided it to customers under the name
IBSYS.
As software became more complex and important, the cost of supporting it on so many different designs became burdensome, and this was one of the factors which led IBM to develop
System/360
The IBM System/360 (S/360) is a family of mainframe computer systems announced by IBM on April 7, 1964, and delivered between 1965 and 1978. System/360 was the first family of computers designed to cover both commercial and scientific applicati ...
and its operating systems.
The
second generation (transistor-based) products were a mainstay of IBM's business and IBM continued to make them for several years after the introduction of the System/360. (Some
IBM 7094
The IBM 7090 is a second-generation transistorized version of the earlier IBM 709 vacuum tube mainframe computer that was designed for "large-scale scientific and technological applications". The 7090 is the fourth member of the IBM 700/7000 se ...
s remained in service into the 1980s.)
Smaller machines

Prior to System/360, IBM also sold computers smaller in scale that were not considered mainframes, though they were still bulky and expensive by modern standards. These included:
*
IBM 650
The IBM 650 Magnetic Drum Data-Processing Machine is an early digital computer produced by IBM in the mid-1950s. It was the first mass-produced computer in the world. Almost 2,000 systems were produced, the last in 1962, and it was the firs ...
(vacuum tube logic,
decimal architecture,
drum memory
Drum memory was a magnetic data storage device invented by Gustav Tauschek in 1932 in Austria. Drums were widely used in the 1950s and into the 1960s as computer memory.
Many early computers, called drum computers or drum machines, used drum ...
, business and scientific)
*
IBM 305 RAMAC
The IBM 305 RAMAC was the first commercial computer that used a moving-head hard disk drive (magnetic disk storage) for secondary storage. The system was publicly announced on September 14, 1956, (vacuum tube logic, first computer with
disk storage
Disc or disk may refer to:
* Disk (mathematics)
In geometry, a disk (Spelling of disc, also spelled disc) is the region in a plane (geometry), plane bounded by a circle. A disk is said to be ''closed'' if it contains the circle that constitut ...
; ''see:''
Early IBM disk storage
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 for ...
)
*
IBM 1400 series
The IBM 1400 series are 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 ...
(business data processing; very successful and many 1400 peripherals were used with the 360s)
*
IBM 1620
The IBM 1620 was a model of scientific minicomputer produced by IBM. It was announced on October 21, 1959, and was then marketed as an inexpensive scientific computer. After a total production of about two thousand machines, it was withdrawn on N ...
(decimal architecture, engineering, scientific, and education)
IBM had difficulty getting customers to upgrade from the smaller machines to the mainframes because so much software had to be rewritten. The 7010 was introduced in 1962 as a mainframe-sized 1410. The later Systems 360 and 370 could emulate the 1400 machines. A desk-size machine with a different instruction set, the
IBM 1130, was released concurrently with the System/360 to address the niche occupied by the 1620. It used the same
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 si ...
character encoding as the 360 and was mostly programmed in
Fortran, which was relatively easy to adapt to larger machines when necessary.
IBM also introduced smaller machines after S/360. These included:
*
IBM System/7
The IBM System/7 was a computer system designed for industrial control, announced on October 28, 1970 and first shipped in 1971. It was a 16-bit machine and one of the first made by IBM to use novel semiconductor memory, instead of magnetic core m ...
(semiconductor memory, process control, incompatible replacement for
IBM 1800
The IBM 1800 Data Acquisition and Control System (DACS) was a process control variant of the IBM 1130 with two extra instructions (CMP and DCM), extra I/O capabilities, 'selector channel like' cycle-stealing capability and three hardware index reg ...
*
IBM Series/1
The IBM Series/1 is a 16-bit minicomputer, introduced in 1976, that in many respects competed with other minicomputers of the time, such as the PDP-11 from Digital Equipment Corporation and similar offerings from Data General and HP. The Ser ...
*
IBM 3790
*
IBM 8100
*
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 ...
(Introduced 96 column card)
''Midrange computer'' is a designation used by IBM for a class of computer systems which fall in between mainframes and microcomputers.
IBM System/360

IBM announced the System/360 (S/360) line of mainframes in April 1964. The System/360 was a single series of compatible models for both commercial and scientific use. The number "
360
360 may refer to:
* 360 (number)
* 360 AD, a year
* 360 BC, a year
* 360 degrees, a turn
Businesses and organizations
* 360 Architecture, an American architectural design firm
* Ngong Ping 360, a tourism project in Lantau Island, Hong Kong
...
" suggested a "360
degree," or "all-around" computer system. System/360 incorporated features which had previously been present on only either the commercial line (such as decimal arithmetic and byte addressing) or the engineering and scientific line (such as
floating-point arithmetic
In computing, floating-point arithmetic (FP) is arithmetic on subsets of real numbers formed by a ''significand'' (a Sign (mathematics), signed sequence of a fixed number of digits in some Radix, base) multiplied by an integer power of that ba ...
). Some of the arithmetic units and addressing features were optional on some models of the System/360. However, models were upward compatible and most were also downward compatible. The System/360 was also the first computer in wide use to include dedicated hardware provisions for the use of
operating system
An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs.
Time-sharing operating systems scheduler (computing), schedule tasks for ...
s. Among these were supervisor and application mode programs and instructions, as well as built-in memory protection facilities. Hardware memory protection was provided to protect the operating system from the user programs (tasks) and user tasks from each other. The new machine also had a larger
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 ...
than the older mainframes, 24 bits addressing 8-bit bytes vs. a typical 18 bits addressing 36-bit words.
The smaller models in the System/360 line (e.g. the 360/30) were intended to replace the 1400 series while providing an easier upgrade path to the larger 360s. To smooth the transition from the second generation to the new line, IBM used the 360's
microprogramming capability to emulate the more popular older models. Thus 360/30s with this added cost feature could run 1401 programs and the larger 360/65s could run 7094 programs. To run old programs, the 360 had to be halted and restarted in emulation mode. Many customers kept using their old software and one of the features of the later System/370 was the ability to switch to emulation mode and back under operating system control.
Operating systems for the System/360 family included
OS/360
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/IBJOB a ...
(with PCP, MFT, and
MVT),
BOS/360,
TOS/360, and
DOS/360
Disk Operating System/360, also DOS/360, or simply DOS, is the discontinued first member of a sequence of operating systems for IBM System/360, System/370 and later mainframes. It was announced by IBM on the last day of 1964, and it was first d ...
.
The System/360 later evolved into the
System/370
The IBM System/370 (S/370) is a range of IBM mainframe computers announced as the successors to the IBM System/360, System/360 family on June 30, 1970. The series mostly maintains backward compatibility with the S/360, allowing an easy migrati ...
, the
System/390, and the
64-bit
In computer architecture, 64-bit integers, memory addresses, or other data units are those that are 64 bits wide. Also, 64-bit central processing units (CPU) and arithmetic logic units (ALU) are those that are based on processor registers, a ...
zSeries, System z, and zEnterprise machines. System/370 introduced
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 ver ...
capabilities in all models other than the first System/370 models; the
OS/VS1 variant of OS/360 MFT, the
OS/VS2 (SVS) variant of OS/360 MVT, and the DOS/VS variant of DOS/360 were introduced to use the virtual memory capabilities, followed by
MVS, which, unlike the earlier virtual-memory operating systems, ran separate programs in separate address spaces, rather than running all programs in a single virtual address space. The virtual memory capabilities also allowed the system to support
virtual machine
In computing, a virtual machine (VM) is the virtualization or emulator, emulation of a computer system. Virtual machines are based on computer architectures and provide the functionality of a physical computer. Their implementations may involve ...
s; the
VM/370 hypervisor
A hypervisor, also known as a virtual machine monitor (VMM) or virtualizer, is a type of computer software, firmware or hardware that creates and runs virtual machines. A computer on which a hypervisor runs one or more virtual machines is called ...
would run one or more virtual machines running either standard System/360 or System/370 operating systems or the single-user
Conversational Monitor System
The Conversational Monitor System (CMS, originally Cambridge Monitor System) is a simple interactive single-user operating system. CMS was originally developed as part of IBM's CP/CMS operating system, which went into production use in 1967. ...
(CMS). A
time-sharing
In computing, time-sharing is the Concurrency (computer science), concurrent sharing of a computing resource among many tasks or users by giving each Process (computing), task or User (computing), user a small slice of CPU time, processing time. ...
VM system could run multiple virtual machines, one per user, with each virtual machine running an instance of CMS.
Today's systems

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 will soon include the newes ...
family, introduced in 2000 with the z900, supports
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/Architecture ...
, which extends the architecture used by the System/390 mainframes to 64 bits.
Processor units
The different processors on current IBM mainframes are:
* CP,
central processor: general-purpose processor
* IFL,
Integrated Facility for Linux
The Integrated Facility for Linux (IFL) is an IBM mainframe and Power Systems processor dedicated to running the Linux operating system. On IBM Z and IBM LinuxONE machines, IFLs can be used with or without hypervisors such as z/VM and KVM. ...
: dedicated to
Linux
Linux ( ) is a family of open source Unix-like operating systems based on the Linux kernel, an kernel (operating system), operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically package manager, pac ...
OSes (optionally under
z/VM
z/VM is the current version in IBM's VM family of virtual machine operating systems. First released in October 2000, z/VM remains in active use and development . It is directly based on technology and concepts dating back to the 1960s, particu ...
)
* ICF, Integrated
Coupling Facility
In IBM System/390 and IBM Z mainframe computers, a Coupling Facility or CF is a piece of computer hardware or virtual machine that coordinates multiple processors.
A Parallel Sysplex
relies on one or more Coupling Facilities (CFs). A coupling ...
: designed to support
Parallel Sysplex operations
* SAP, System Assist Processor: designed to handle various system accounting, management, and
I/O channel operations
*
zAAP, System z Application Assist Processor: currently limited to run only
Java
Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...
and
XML
Extensible Markup Language (XML) is a markup language and file format for storing, transmitting, and reconstructing data. It defines a set of rules for encoding electronic document, documents in a format that is both human-readable and Machine-r ...
processing
*
zIIP
In IBM System z9 and successor mainframes, the System z Integrated Information Processor (zIIP) is a special purpose processor. It was initially introduced to relieve the general mainframe central processors (CPs) of specific Db2 processing load ...
, System z Integrated Information Processor: dedicated to run specific workloads including
IBM Db2,
XML
Extensible Markup Language (XML) is a markup language and file format for storing, transmitting, and reconstructing data. It defines a set of rules for encoding electronic document, documents in a format that is both human-readable and Machine-r ...
, and
IPSec
These are essentially identical, but distinguished for software cost control: all but CP are slightly restricted such they cannot be used to run arbitrary operating systems, and thus do not count in software licensing costs (which are typically based on the number of CPs).
There are other supporting processors typically installed inside mainframes such as
cryptographic
Cryptography, or cryptology (from "hidden, secret"; and ''graphein'', "to write", or '' -logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of adversarial behavior. More gen ...
accelerators (
CryptoExpress), the
OSA-Express networking processor, and
FICON
FICON (Fibre Connection) is the IBM proprietary name for the ANSI ''FC-SB-3 Single-Byte Command Code Sets-3 Mapping Protocol'' for Fibre Channel (FC) protocol. It is a FC layer 4 protocol used to map both IBM's antecedent (either ESCON or para ...
Express disk I/O processors.
Software to allow users to run "traditional" workloads on zIIPs and zAAPs was briefly marketed by Neon Enterprise Software as "zPrime" but was withdrawn from the market in 2011 after a lawsuit by IBM.
Operating systems
The primary
operating system
An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs.
Time-sharing operating systems scheduler (computing), schedule tasks for ...
s in use on current IBM mainframes include
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:
...
(which followed
MVS/ESA and
OS/390 in the
OS/360
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/IBJOB a ...
lineage),
z/VM
z/VM is the current version in IBM's VM family of virtual machine operating systems. First released in October 2000, z/VM remains in active use and development . It is directly based on technology and concepts dating back to the 1960s, particu ...
(which followed
VM/ESA and VM/XA SP in the
CP-40 lineage),
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. It is less common than z/OS and is mostly used on smaller machines.
DOS/VSE was introduced i ...
(which is in the
DOS/360 lineage),
z/TPF (a successor of Transaction Processing Facility in the
Airlines Control Program lineage), and
Linux on IBM Z
Linux ( ) is a family of open source Unix-like operating systems based on the Linux kernel, an kernel (operating system), operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically package manager, pac ...
(e.g.,
Debian
Debian () is a free and open-source software, free and open source Linux distribution, developed by the Debian Project, which was established by Ian Murdock in August 1993. Debian is one of the oldest operating systems based on the Linux kerne ...
,
Red Hat Enterprise Linux
Red Hat Enterprise Linux (RHEL) is a commercial Linux distribution developed by Red Hat. Red Hat Enterprise Linux is released in server versions for x86-64, Power ISA, ARM64, and IBM Z and a desktop version for x86-64. Fedora Linux and ...
,
SUSE Linux Enterprise Server
SUSE Linux Enterprise (SLE) is a Linux-based operating system developed by SUSE. It is available in two editions, suffixed with Server (SLES) for servers and mainframes, and Desktop (SLED) for workstations and desktop computers.
Its major ve ...
). Some systems run
MUSIC/SP, as well as
UTS (Mainframe UNIX). In October 2008, Sine Nomine Associates introduced
OpenSolaris on System z; it has since been discontinued.
Middleware
Current IBM mainframes run all the major enterprise
transaction processing
In computer science, transaction processing is information processing that is divided into individual, indivisible operations called ''transactions''. Each transaction must succeed or fail as a complete unit; it can never be only partially c ...
environments and
database
In computing, a database is an organized collection of data or a type of data store based on the use of a database management system (DBMS), the software that interacts with end users, applications, and the database itself to capture and a ...
s, including
CICS
IBM CICS (Customer Information Control System) is a family of mixed-language application servers that provide online business transaction management, transaction management and connectivity for applications on IBM mainframe systems under z/OS ...
,
IMS,
WebSphere Application Server,
IBM Db2, and
Oracle
An oracle is a person or thing considered to provide insight, wise counsel or prophetic predictions, most notably including precognition of the future, inspired by deities. If done through occultic means, it is a form of divination.
Descript ...
. In many cases these
software
Software consists of computer programs that instruct the Execution (computing), execution of a computer. Software also includes design documents and specifications.
The history of software is closely tied to the development of digital comput ...
subsystems can run on more than one mainframe operating system.
Emulators
There are software-based emulators for the System/370, System/390, and System z hardware, including
FLEX-ES, which runs under
UnixWare or
Linux
Linux ( ) is a family of open source Unix-like operating systems based on the Linux kernel, an kernel (operating system), operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically package manager, pac ...
, and the freely available
Hercules
Hercules (, ) is the Roman equivalent of the Greek divine hero Heracles, son of Jupiter and the mortal Alcmena. In classical mythology, Hercules is famous for his strength and for his numerous far-ranging adventures.
The Romans adapted the Gr ...
, which runs under
Linux
Linux ( ) is a family of open source Unix-like operating systems based on the Linux kernel, an kernel (operating system), operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically package manager, pac ...
,
FreeBSD
FreeBSD is a free-software Unix-like operating system descended from the Berkeley Software Distribution (BSD). The first version was released in 1993 developed from 386BSD, one of the first fully functional and free Unix clones on affordable ...
,
Solaris
Solaris is the Latin word for sun.
It may refer to:
Arts and entertainment Literature, television and film
* ''Solaris'' (novel), a 1961 science fiction novel by Stanisław Lem
** ''Solaris'' (1968 film), directed by Boris Nirenburg
** ''Sol ...
,
macOS
macOS, previously OS X and originally Mac OS X, is a Unix, Unix-based operating system developed and marketed by Apple Inc., Apple since 2001. It is the current operating system for Apple's Mac (computer), Mac computers. With ...
and
Microsoft Windows
Windows is a Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sec ...
.
IBM offers an emulator called zPDT (System z Personal Development Tool) which runs on Linux on
x86-64
x86-64 (also known as x64, x86_64, AMD64, and Intel 64) is a 64-bit extension of the x86 instruction set architecture, instruction set. It was announced in 1999 and first available in the AMD Opteron family in 2003. It introduces two new ope ...
machines.
See also
*
List of IBM products
The list of IBM products is a partial list of products, services, and subsidiaries of IBM, International Business Machines (IBM) Corporation and its predecessor corporations, beginning in the 1890s.
Context
Products, services, and subsidiari ...
*
Amdahl Corporation
Amdahl Corporation was an information technology company which specialized in IBM mainframe-compatible computer products, some of which were regarded as supercomputers competing with those from Cray Research. Founded in 1970 by Gene Amdahl, a for ...
*
IBM midrange computer
*
IBM LinuxONE
*
IBM Secure Service Container
*
Input/Output Configuration Program
Notes
References
Further reading
*
* Prasad, Nallur and Savit, Jeffrey (1994). ''IBM Mainframes: Architecture and Design'', 2nd ed. McGraw-Hill Osborne Media. .
*
External links
Official IBM mainframe page (IBM Z)IBM Mainframe Resources & Forum
{{DEFAULTSORT:Ibm Mainframe
Computer-related introductions in 1952