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Minicomputer

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Minicomputer (colloquially, mini) is a largely obsolete term for a class of multi-user computers which make up the middle range of the computing spectrum, in between the largest multi-user systems (traditionally, mainframe computers) and the smallest single-user systems (microcomputers or personal computers). More modern terms for such machines include midrange systems (common in IBM parlance), workstations (common in Sun Microsystems and general UNIX/Linux parlance), and servers.

1 History
2 List of some notable minicomputers
3 See also

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History

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1960s: Origin; 1970s: Market entrenchment

The term "minicomputer" evolved in the 1960s to describe the "small" third generation computers that became possible with the use of transistor and core memory technologies. The term came in fashion about the same time as the miniskirt and mini cars. They usually took up one or a few cabinets the size of a large refrigerator or two, compared with mainframes that would usually fill a room. The first successful minicomputer was Digital Equipment Corporation's 12-bit PDP-8, which cost from US$16,000 upwards when launched in 1964.

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 (Very Large Scale Integration), often making the hardware organization much less apparent.)

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 like VMS and Unix. The classical mini was a 16-bit computer, while the emerging higher performance 32-bit minis were often referred to as superminis.

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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, and the desire of end-users to be less reliant on inflexible minicomputer manufacturers and IT departments/"data centers"—with the result that minicomputers and dumb terminals were replaced by networked workstations and PCs 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, Linux, FreeBSD, NetBSD and OpenBSD. Also, the Microsoft Windows series of operating systems now includes server versions that support preemptive multitasking and other features required for servers, beginning with Windows NT.

As microprocessors have become more powerful, 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 the leading minicomputer manufacturer, at one time the 2nd 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 Computer, many based in New England also collapsed as DEC was sold to Compaq in 1998.

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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 first microcomputer operating system, CP/M was an implementation of a DEC PDP-11 operating system for the 8080 and Z80 processors. DOS, which gives its command line to Windows, was an unauthorized port / redesign of CP/M for the 8086. The Windows NT operating system was headed by a designer from DEC responsible for the VMS OS for the VAX minicomputer range in the 1970s, and adopted features from UNIX which ran largely on minicomputers.

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