Minicomputer

 

For small modern computers, see Small form factor, nettop, etc.

First generation Digital Equipment Corporation (DEC) PDP-8 on display at the National Museum of American History

Data General Nova, serial number 1, the first 16-bit minicomputer, on display at the Computer History Museum

A PDP-11, model 40, an early member of DECs 16-bit minicomputer family, on display at the Vienna Technical Museum

The word "minicomputer" (colloquially, "mini") is a term for a class of smaller computers that evolved in the mid-1960s and sold for much less than mainframe and mid-size computers from IBM and its direct competitors. In a 1970 survey, the New York Times suggested a consensus definition of a minicomputer as a machine costing less than $25,000, with an input-output device such as a teleprinter and at least 4K words of memory, that is capable of running programs in a higher level language, such as Fortran or Basic. The class formed a distinct group with its own hardware architectures and operating systems.

When single-chip CPUs appeared, beginning with the Intel 4004 in 1971, the term "minicomputer" came to mean a machine that lies in the middle range of the computing spectrum, in between the smallest mainframe computers and the microcomputers. The term "minicomputer" is little used today; the contemporary term for this class of system is "midrange computer", such as the higher-end SPARC, POWER and Itanium-based systems from Oracle, IBM and Hewlett-Packard.

History

1960s: Origin; 1970s: Market entrenchment

The term "minicomputer" evolved in the 1960s to describe the smaller computers that became possible with the use of transistors and core memory technologies, minimal instructions sets and less expensive peripherals such as the ubiquitous Teletype Model 33 ASR. They usually took up one or a few 19-inch rack cabinets, compared with the large mainframes that could fill a room. The first successful minicomputer was Digital Equipment Corporation's 12-bit PDP-8, which was built using discrete transistors and cost from US$16,000 upwards when launched in 1964. Later versions of the PDP-8 took advantage of small-scale integrated circuits. The important precursors of the PDP-8 include the PDP-5, LINC, the TX-0, the TX-2, and the PDP-1. Digital Equipment gave rise to a number of minicomputer companies along Massachusetts Route 128, including Data General, Wang Laboratories, Apollo Computer, and Prime Computer.

Minicomputers were also known as midrange computers. They grew to have relatively high processing power and capacity. 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 the computer-aided design (CAD) industry and other similar industries where a smaller dedicated system was needed.

The 7400 series of TTL integrated circuits started appearing in minicomputers in the late 1960s. The 74181 arithmetic logic unit (ALU) was commonly used in the CPU data paths. Each 74181 had a bus width of four bits, hence the popularity of bit-slice architecture. The 7400 series offered data-selectors, multiplexers, three-state buffers, memories, etc. in dual in-line packages with one-tenth inch spacing, making major system components and architecture evident to the naked eye. Starting in the 1980s, many minicomputers used VLSI circuits.

As microcomputers developed in the 1970s and 80s, minicomputers filled the mid-range area between low-powered microcomputers and high-capacity mainframes. At the time, microcomputers were single-user, relatively simple machines running simple program-launcher operating systems like CP/M or MS-DOS, while minis were much more powerful systems that ran full multi-user, multitasking operating systems, such as VMS and Unix, often with timesharing versions of BASIC for application development (MAI Basic Four systems being very popular in that regard). The classical mini was a 16-bit computer, while the emerging higher performance 32-bit minis were often referred to as superminis.

At the launch of the MITS Altair 8800 in 1975, Radio Electronics magazine referred to the system as a "minicomputer", although it would properly be called a microcomputer; as it was the first commercially available personal computer based on the single-chip microprocessor from Intel.

Mid-1980s, 1990s: The minis give way to the micros

The decline of the minis happened due to the lower cost of microprocessor-based hardware, the emergence of inexpensive and easily deployable local area network systems, the emergence of the 68020, 80286 and the 80386 microprocessors, and the desire of end-users to be less reliant on inflexible minicomputer manufacturers and IT departments or "data centers". The result was that minicomputers and computer terminals were replaced by networked workstations, file servers and PCs in some installations, beginning in the latter half of the 1980s.

During the 1990s, the change from minicomputers to inexpensive PC networks was cemented by the development of several versions of Unix to run on the Intel x86 microprocessor architecture, including Solaris, FreeBSD, NetBSD and OpenBSD. Also, the Microsoft Windows series of operating systems, beginning with Windows NT, now included server versions that supported preemptive multitasking and other features required for servers.

As microprocessors have become more powerful, the CPUs built up from multiple components – once the distinguishing feature differentiating mainframes and midrange systems from microcomputers – have become increasingly obsolete, even in the largest mainframe computers.

Digital Equipment Corporation was once the leading minicomputer manufacturer, at one time the second-largest computer company after IBM. But as the minicomputer declined in the face of generic Unix servers and Intel-based PCs, not only DEC, but almost every other minicomputer company including Data General, Prime, Computervision, Honeywell and Wang Laboratories, many based in New England, also collapsed or merged. DEC was sold to Compaq in 1998.

Today only a few proprietary minicomputer architectures survive. The IBM System/38 operating system, which introduced many advanced concepts, lives on with IBM's AS/400. Realising the importance of the thousands of lines of 'legacy code' (programs) written, 'AS' stands for 'Application System'. Great efforts were made by IBM to enable programs originally written for the System/34 and System/36 to be moved to the AS/400. The AS/400 was replaced by the iSeries, which was subsequently replaced by the System i. In 2008, the System i was replaced by the IBM POWER Systems. By contrast, competing proprietary computing architectures from the early 1980s, such as DEC's VAX, Wang VS and Hewlett Packard's HP3000 have long been discontinued without a compatible upgrade path. OpenVMS runs HP Alpha and Intel IA64 (Itanium) CPU architectures.

Tandem Computers, which specialized in reliable large-scale computing, was acquired by Hewlett Packard. The NSK-based NonStop product line was re-ported from MIPS processors to Itanium-based processors branded as 'HP Integrity NonStop Servers'. As in the earlier migration from stack machines to MIPS microprocessors, all customer software was carried forward without source changes. Integrity NonStop continues to be HP's answer for the extreme scaling needs of its very largest customers. The NSK operating system, now termed NonStop OS, continues as the base software environment for the NonStop Servers, and has been extended to include support for Java and integration with popular development tools like Visual Studio and Eclipse.

The minicomputer's industrial impact and heritage

Several pioneering computer companies first built minicomputers, such as DEC, Data General, and Hewlett-Packard (HP) (who now refers to its HP3000 minicomputers as "servers" rather than "minicomputers"). And although today's PCs and servers are clearly microcomputers physically, architecturally their CPUs and operating systems have evolved largely by integrating features from minicomputers.

In the software context, the relatively simple OSs for early microcomputers were usually inspired by minicomputer OSs (such as CP/M's similarity to Digital's RSTS). Also, the multiuser OSs of today are often either inspired by, or directly descended from, minicomputer OSs. UNIX was originally a minicomputer OS, while Windows NT—the foundation for all current versions of Microsoft Windows—borrowed design ideas liberally from VMS and UNIX. Many of the first generation of PC programmers were educated on minicomputer systems.^{[citation needed]}.

List of some notable minicomputers

• Control Data's CDC 160A and CDC 1700
• DEC PDP and VAX series
• Data General Nova
• Hewlett-Packard HP 3000 series, HP 2100 series, HP1000 series.
• Honeywell-Bull Level 6/DPS 6/DPS 6000 series
• IBM midrange computers
• Norsk Data Nord-1, Nord-10, and Nord-100
• Prime Computer Prime 50 series
• SDS SDS-92
• SEL, one of the first 32-bit real-time computer system manufacturers
• Texas Instruments TI-990
• Wang Laboratories 2200 and VS series
• K-202, first Polish minicomputer and probably first personal computer

See also

• The Soul of a New Machine – about the development of Data General’s Eclipse/MV minicomputers in the early 1980s
• Charles Babbage Institute
• History of computing hardware (1960s-present)
• Superminicomputer

External links

• Early mini computers, still runnable in a German computer museum
• A list of Minicomputers
• Modern Minicomputers