Computers and Computer Systems IV

TYPES OF COMPUTERS

THE MINICOMPUTER.

Until the 1960s all computers were mainframes. They were large and costly systems intended to support many users, sometimes numbering in the hundreds or thousands. A new class of computers, the minicomputer, was introduced in December 1959 with the launch of the PDP-1 by Digital Equipment Corp. (DEC). However, the term "minicomputer" wasn't used until the introduction of the PDP-5 in 1963. These computers were smaller and cheaper than mainframes, and were also programmed to be used interactively, i.e., in real time, instead of in batch mode. Soon after, Hewlett-Packard Co. and Data General also introduced minicomputers, and eventually Wang, Tandem, Datapoint, Prime, and IBM followed suit.

The distinction between the better minicomputers and the lesser mainframes was largely one of marketing. Generally, minicomputers performed the same functions as mainframes but had less storage capacity, processing power, and speed. Traditionally minicomputers had 16-bit processors (as did PCs by the early 1990s), but later ones were 32-bit (as were PCs by the mid-1990s). By contrast, mainframes tended to have 32-bit and 64-bit processors.

Minicomputers became predominant in the 1970s and served a broad range of businesses. The most widely used included the DEC VAX, starting with the VAX-11/780 in 1977, a 32-bit computer that ran DEC's proprietary VMS operating system. The IBM AS/400, introduced in 1988, was one of the most popular minicomputers for small to medium workloads. More recently, the label "midrange systems" has been used more frequently to describe minicomputers.

•Mainframes—high-capacity, expensive systems with centralized processing power, usually accessed by terminals or PCs running emulation software, that can run multiple programs at once. Examples: IBM System/390, Amdahl Millennium 2000.

•Mini/Midrange Computers—synonymous terms for powerful computers that can host a range of simultaneous users, such as for network servers or small to mid-size database management systems. Examples: IBM AS/400, Hewlett-Packard 3000.

•Microcomputers/PCs—desktop and portable computers with extensive built-in processing and storage capabilities. Examples: Compaq Presario, Dell Dimension, Apple Macintosh G3.

•Workstations—powerful desktop machines, often containing multiple processors and running Unix or Windows NT, for resource-intensive business or scientific applications. Examples: IBM IntelliStation, Silicon Graphics 02 R10000, Sun UltraSparc.

•Network Computers/Thin Clients—scaled-back PC-like devices with less on-board processing power and little or no local storage of programs or data, which are instead housed in a central computer and accessed through simple, universal software tools, such as Web browsers. Examples: IBM Network Station, Sun JavaStation.

THE MICROCOMPUTER.

The development of the microprocessor, a CPU on a single integrated circuit chip, enabled the development of affordable single-user microcomputers. The slow processing power of the early microcomputers, however, made them attractive only to hobbyists and not to the business market. The first microprocessor, introduced by Intel Corp. in 1970, could handle only 4 bits at a time. Later Intel introduced the 8000 series of 8-bit microprocessors. The Altair 8800 was introduced in 1974 and was the first commercially successful microcomputer, although in keeping with the interests of the hobby market, it was actually a kit. In 1977 the personal computer industry got under way with the introduction of off-the-shelf home computers from three separate manufacturers: Commodore Business Machines, Inc.'s PET; Apple Computer, Inc.'s Apple II; and Tandy Corp.'s TRS-80. These were each 8-bit computers that had a maximum of 64 kilobytes of memory and used only floppy disks for storage, instead of an internal hard disk. Popular home computers at the beginning of the 1980s included the Commodore 64 and 128, the Apple 11, and the Atari 500. A software package from Digital Research, Inc. (later acquired by Novell Inc.) known as CP/M, which stood for Control Program/Microprocessor, was the dominant operating system of microcomputers at this time.

In 1979 one of the most important advances for microcomputers came not in hardware, but in software. That year Software Arts, Inc. introduced the world's first spreadsheet software, VisiCalc. Though crude by modem standards, VisiCalc provided a level of interactivity and productivity that was truly unique at the time. With VisiCalc, businesses for the first time had a reason to seriously consider buying a microcomputer, as even mainframes didn't allow users to sit down and chum out a series of user-defined calculations on the spot. VisiCalc was originally developed for the Apple II, but competing spreadsheets were soon developed for other systems, notably 1-2-3 by Lotus Development Corp. (later a unit of IBM).

The familiar term "personal computer" (PC) was coined by IBM with the 1981 launch of its first microcomputer, which was an instant success and helped set new standards for the industry. This was a second major event, after the creation of productivity applications, that helped raise widespread interest in microcomputers, as IBM's name—and marketing channels—signaled legitimacy for business uses. The term PC came to be used for microcomputers generally, and it was also used specifically to designate computers that were compatible with the IBM standard, which was based on the Intel 80x86 chip and Microsoft Corp.'s MS-DOS (Microsoft Disk Operating System). IBM's choice of Microsoft as its operating system vendor was pivotal in the latter's ascent in the software industry, which later would reach monopoly status. By the late 1980s, MS-DOS had overtaken CP/M as the dominant operating system.

Meanwhile, one notable exception to the industry's coalescence around the IBM/Intel/Microsoft axis was Apple Computer's Macintosh line, introduced in 1984. The Mac was based on Apple's own proprietary operating system and graphical user interface called MacOS. The graphical interface attracted a limited but devoted following for the Mac, mostly from schools and businesses engaged in desktop publishing and other graphical work. It wasn't until the 1990s, with the release of advanced versions of Microsoft's Windows operating system that IBM-compatible PCs would begin to approximate the ease of use Mac users enjoyed. However, new applications and enhancements for the Macintosh platform were slow to develop because Apple chose not to make its operating system available for other developers to freely license and adapt programs to—as Microsoft had done with DOS and Windows—preferring instead to keep tighter control over its product.

By the early 1990s IBM-compatible PCs, which by then were 16-bit or 32-bit machines, had become the fastest growing category of computers. This was largely fueled by business adoption of PCs. Their availability, ease of set-up and operation, and relative low cost brought computer technology to even the smallest of enterprises. The middle and late 1990s saw a race among computer makers to beef up the performance of their PCs and components to improve speed, networking abilities, and multimedia capabilities. By the end of the decade, top-level consumer and business PCs had processors with clock speeds upwards of 500 megahertz (MHz), up from just 66 or less five or six years before. RAM use also skyrocketed, averaging 32 to 64 megabytes, versus just 4 or 8 megabytes earlier in the decade.

WORKSTATIONS.

Workstations are a special class of high-end microcomputers. Some workstations, in fact, are indistinguishable from less powerful midrange computers. Workstations are typically used as standalone machines, albeit usually networked, for resource-intensive applications like computer-aided design, three-dimensional modeling and simulation, and other demanding engineering, scientific, and graphical tasks.

The workstation was first introduced in 1980 by Apollo Computer, which was later absorbed by Hewlett-Packard. It was Sun Microsystems, Inc., though, founded two years later, that soon dominated this market segment by producing affordable workstations from standard, off-the-shelf parts and using an adaptation of the versatile and powerful Unix operating system, which had been developed originally by Bell Laboratories. Workstation performance was further enhanced with the adoption of a microprocessor based on reduced instruction set computing (RISC) architecture, pioneered by IBM in 1986. RISC enabled faster processing by limiting the complexity and diversity of instructions the processor handled. (RISC would later reach the general PC market only in the advanced versions of Intel's Pentium chips and related competitors in the mid-1990s). Sun introduced its first RISC-based workstation, the SPARCstation, in 1989. Soon, other workstation manufacturers such as Hewlett-Packard followed Sun's lead by combining RISC hardware and Unix software. This emergent standard helped generate interest in workstations by making them more compatible and consistent across manufacturers.