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Aminicomputer, or colloquiallymini, is a type of general-purpose computer mostly developed from the mid-1960s,[1][2] built significantly smaller and sold at a much lower price thanmainframe computers.[3] Minicomputers are small relative to earlier and bigger machines.[4]
The class formed a distinct group with its own software architectures and operating systems. Minis were designed for control, instrumentation, human interaction, and communication switching, as distinct from calculation andrecord keeping. Many were sold indirectly tooriginal equipment manufacturers (OEMs) for final end-use application. During the two-decade lifetime of the minicomputer class (1965–1985), almost 100 minicomputer vendor companies formed. Only a half-dozen remained by the mid-1980s.[5]
When single-chipMOSFETCPUmicroprocessors appeared in the 1970s, the definition of "minicomputer" subtly shifted: the word came to mean a machine in the middle range of the computing spectrum, betweenmainframe computers andmicrocomputers. The easily-misunderstood term "minicomputer" is less often applied to later like systems; a near-synonymous (IBM-adjacent) expert term for this class of system is "midrange computer".
The term "minicomputer" developed in the 1960s[6] to describe the smaller computers that became possible with the use oftransistors andcore memory technologies, minimalinstruction sets and less expensiveperipherals such as the ubiquitousTeletype Model 33 ASR.[5][7] They usually took up one or a few19-inch rack cabinets, compared with the largemainframes that could fill a room.[8] Later minicomputers tended to be more compact, and while still distinct in terms ofarchitecture and function, some models eventually shrank to a similar size as large microcomputers.
In terms of relative computing power compared to contemporary mainframes, small systems that were similar to minicomputers had been available from the 1950s. In particular, there was an entire class of compactvacuum tube-baseddrum machines, such as theUNIVAC 1101 (1950), and theBendix G-15 andLGP-30 (both 1956), all of which shared some features of the minicomputer class. Similar models using magneticdelay-line memory followed in the early 1960s. These machines, however, were essentially designed as small mainframes, using a custom chassis and often supporting only peripherals from the same company. In contrast, the machines that became known as minicomputers were often designed to fit into a standard chassis and deliberately designed to use common devices such as the ASR 33.
Another common difference was that most small machines before the 1970s were not "general purpose", in that they were designed for a specific role such as engineering,[9]: 13 process control or accounting. On these machines, programming was generally carried out in their custommachine language, or even hard-coded into aplugboard, although some used a form ofBASIC.[citation needed][example needed] DEC wrote, regarding their PDP-5, that it was "the world’s first commercially produced minicomputer".[10] It meets most definitions of "mini" in terms of power and size, but was designed and built to be used as an instrumentation system in labs, not as a general-purpose computer.[11] Many similar examples of small special-purpose machines exist from the early 1960s, including the UKFerranti Argus and Soviet UM-1NKh.
TheCDC 160, circa 1960, is sometimes pointed to as an early example of a minicomputer, as it was small, transistorized and (relatively) inexpensive. However, its basic price of $100,000 (equivalent to $1,062,880 in 2024) and custom desk-like chassis places it within the "small system" or "midrange computer"[12] category as opposed to the more modern use of the term minicomputer. Nevertheless, the CDC 160 remains a strong contender for the term "first minicomputer",[11] provided the earlier drum machines, e.g.SEA CAB 500, are excluded as non-transistorized.
Most computing histories point to the 1964 introduction ofDigital Equipment Corporation's (DEC)Programmed Data Processor (PDP) series, with the12-bitPDP-8 as the first minicomputer.[13] Some of this is no doubt due to DEC's widespread use of the term starting in the mid-1960s.[14] Smaller systems, including those from DEC such as thePDP-5 andLINC,[15] had existed prior to this point, but it was the PDP-8 combination of small size, general purpose orientation and low price that puts it firmly within the modern definition. Its introductory price of $18,500[16] (equivalent to $184,590 in 2024) places it in an entirely different market segment than earlier examples such as the CDC 160.
In contemporary terms, the PDP-8 was a runaway success, ultimately selling 50,000 examples.[a] Follow-on versions using small scaleintegrated circuits further lowered the cost and size of the system. Its success led to widespread imitation, and the creation of an entire industry of minicomputer companies alongMassachusetts Route 128, includingData General,Wang Laboratories andPrime Computer. Other popular minis from the era were theHP 2100,Honeywell 316 andTI-990.
Early minis had a variety ofword sizes, with DEC's 12 and 18-bit systems being typical examples. The introduction and standardization of the 7-bitASCII character set led to the move to 16-bit systems, with the late-1969Data General Nova being a notable entry in this space. By the early 1970s, most minis were 16-bit, including DEC'sPDP-11. For a time, "minicomputer" was almost synonymous with "16-bit", as the larger mainframe machines almost always used 32-bit or larger word sizes.In a 1970 survey,The New York Times suggested a consensus definition of a minicomputer as a machine costing less thanUS$25,000 (equivalent to $202,000 in 2024[17]), with an input-output device such as ateleprinter and at least four thousand words of memory, that is capable of running programs in ahigher level language, such asFortran orBASIC.[18] The typical customer was a department in a large company, at which the finance department's mainframe was too busy to serve others.[9]: 12
Asintegrated circuit design improved, especially with the introduction of the7400-series integrated circuits, minicomputers became smaller, easier to manufacture, and as a result, less expensive. They were used in manufacturing process control, telephone switching and to control laboratory equipment. In the 1970s, they were the hardware that was used to launch thecomputer-aided design (CAD) industry[19] and other similar industries where a small dedicated system was needed.
The boom in worldwideseismic exploration for oil and gas in the early 1970s saw the widespread use of minicomputers in dedicated processing centres close to the data collection crews. Raytheon Data SystemsRDS 704 and later RDS 500 were predominantly the systems of choice for nearly all the geophysical exploration as well as oil companies.[20][21]
At the launch of theMITS Altair 8800 in 1975,Radio Electronics magazine referred to the system as a "minicomputer", although the termmicrocomputer soon became usual forpersonal computers based on single-chipmicroprocessors. At the time, microcomputers were 8-bit single-user, relatively simple machines running simple program-launcher operating systems such asCP/M orMS-DOS, while minis were much more powerful systems that ran fullmulti-user,multitasking operating systems, such asVMS andUnix.
TheTandem ComputersNonStop product line shipped its first fullyfault-tolerantcluster computer in 1976.[22][23][24]
Around the same time, minis began to move upward in size. Although several 24 and 32-bit minis had entered the market earlier, it was DEC's 1977VAX, which they referred to as asuperminicomputer, or supermini, that caused the mini market to move en-masse to32-bit architectures. This provided ample headroom even as single-chip 16-bit microprocessors such as theTMS 9900 andZilog Z8000 appeared in the later 1970s. Most mini vendors introduced their own single-chip processors based on their own architecture and used these mostly in low-cost offerings while concentrating on their 32-bit systems. Examples include theIntersil 6100 single-chip PDP-8,DEC T-11 PDP-11,microNOVA andFairchild 9440 Nova, andTMS9900 TI-990.
Minicomputer companies historically competed on the price and speed of their computers, instead of marketing and advertising.[25] By the early 1980s, the 16-bit minicomputer market had all but disappeared as newer 32-bit microprocessors began to improve in performance. Those customers who required more performance than these offered had generally already moved to 32-bit systems by this time. But it was not long before this market also began to come under threat; theMotorola 68000 offered a significant percentage of the performance of a typical mini in a desktop platform. True 32-bit processors such as theNational Semiconductor NS32016,Motorola 68020 andIntel 80386 soon followed. By the mid-1980s, high-end microcomputers offered CPU performance equal to low-end and mid-range minis, and the newRISC approach promised performance levels well beyond the fastest minis, and even high-end mainframes.
All that really separated micros from the mini market was storage and memory capacity. Both of these began to be addressed through the later 1980s; 1 MB of RAM became typical by around 1987, desktophard drives rapidly pushed past the 100 MB range by 1990, and the introduction of inexpensive and easily deployablelocal area network (LAN) systems provided solutions for those looking for multi-user systems. The introduction ofworkstations opened new markets forgraphics-based systems that the terminal-oriented minis could not even address. Minis remained a force for those using existing software products or those who required high-performance multitasking, but the introduction of neweroperating systems based onUnix began to yield highly practical replacements for these roles as well. Forcomputational science,clusters of commodity PCs largely replaced minicomputers.
Mini vendors began to rapidly disappear through this period.Data General responded to the changing market by focusing entirely on the high-performancefile server market, embracing a role within large LANs that appeared resilient. This did not last;Novell NetWare rapidly pushed such solutions into niche roles, and later versions ofMicrosoft Windows did the same to Novell.DEC decided to move into the large-computer space instead, introducing theVAX 9000 mainframe in 1989, but it was a flop in the market and disappeared after almost no sales. The company then attempted to enter the workstation and server markets with theDEC Alpha, but was too late to save the company, and they eventually sold their remains toCompaq in 1998. By the end of the decade all of the classic vendors were gone;Data General,Prime,Computervision,Honeywell, andWang, failed, merged, or were bought out.
Today, only a few proprietary minicomputer architectures survive. TheIBM System/38 operating system, which introduced many advanced concepts, lives on with IBM'sAS/400. Great efforts were made by IBM to enable programs originally written for theIBM System/34 and System/36 to be moved to the AS/400. After being rebranded multiple times, the AS/400 platform was replaced byIBM Power Systems runningIBM i. In contrast, competing proprietary computing architectures from the early 1980s, such as DEC'sVAX,Wang VS, and Hewlett-Packard'sHP 3000 have long been discontinued without a compatible upgrade path.OpenVMS was ported to HPAlpha and IntelIA-64 (Itanium) CPU architectures, and now runs onx86-64 processors.
Tandem Computers, which specialized in reliable large-scale computing, was acquired byCompaq in 1997, and in 2001 the combined entity merged withHewlett-Packard.[26] The NonStop Kernel-basedNonStop product line was re-ported fromMIPS processors to Itanium-based processors branded as 'HP Integrity NonStop Servers'. As in the earlier migration fromstack machines to MIPS microprocessors, all customer software was carried forward without source changes. The NSK operating system, now termedNonStop OS, continues as the base software environment for the NonStop Servers, and has been extended to include support forJava and integration with popular development tools such asVisual Studio andEclipse. Later, Hewlett-Packard would split into HP and Hewlett-Packard Enterprise. The NonStop products and the DEC products would then be sold by HPE.
Database software[9][page needed] is an example of an area where a variety of companies emerged that builtturnkey systems around minicomputers with specialized software and, in many cases, custom peripherals that addressed specialized problems such ascomputer-aided design,computer-aided manufacturing,process control,manufacturing resource planning, and so on. Many if not most minicomputers were sold through theseoriginal equipment manufacturers andvalue-added resellers.
Several pioneering computer companies first built minicomputers, such asDEC,Data General, andHewlett-Packard (HP) (who later referred to itsHP 3000 minicomputers as "servers" rather than "minicomputers"). And although today's PCs and servers are clearly microcomputers physically, architecturally their CPUs and operating systems have developed largely by integrating features from minicomputers.[citation needed]
In the software context, the relatively simple OSs for early microcomputers were usually inspired by minicomputer OSs (such asCP/M's similarity to Digital's single userOS/8 andRT-11 and multi-userRSTS time-sharing system). Also, the multiuser OSs of today are often either inspired by, or directly descended from, minicomputer OSs.[citation needed]Unix was originally a minicomputer OS, while theWindows NT kernel, the foundation for all current versions ofMicrosoft Windows, borrowed design ideas liberally fromVMS. Many of the first generation of PC programmers were educated on minicomputer systems.[27][28]
John Leng sent back sales reports: 'Here is the latest minicomputer activity in the land of miniskirts as I drive around in my Mini Minor.' The phrase caught on at DEC, and then the industry trade publications grabbed on to it. The age of the minicomputer was born.
Minicomputer... the term was introduced in the mid-1960s.
The term was coined by then DEC UK head John Leng, who sent a sales report saying, "Here is the latest minicomputer activity in the land of miniskirts as I drive around in my Mini Minor".
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