Business Glossary

popular lines of microcomputers manufactured by IBM. There are many variations of each; this article will mention only the most historically important.

The IBM Personal Computer (PC), introduced in 1981,was the first of a family of very popular microcomputers, including not only IBM products but also "clones" (imitations) made by other companies. The original IBM PC used very little proprietary technology. Thus, it was easy for competitors to build compatible machines without violating patents. See clone; PC compatibility.

IBM maintained a high level of upward compatibility within the PC and PS/2 line. This means that later-model machines would run virtually all software written for earlier models. Nowadays, most PCcompatible computers are made by other companies; IBM continues to market PC-compatibles that are very similar to competitors' products.

IBM's two original machines, the PC and PC XT, are virtually identical, featuring 4.77-MHz 8088 microprocessors with an 8-bit bus. The only difference was that the XT had a 10-megabyte hard disk and had eight expansion slots instead of five. The PC AT, introduced in 1984, was the first PC to use the 80286 microprocessor, enabling programs to run much faster. The PC AT had what is now known as the ISA (Industry Standard Architecture) bus; it accepted both 8-bit (XT-style) and 16-bit plug-in cards.

The PS/2 machines were introduced in 1987 and discontinued in 1995. They were more compact than comparably configured PCs or ATs, and all but the lowest models used the Micro Channel bus, which made it possible in some situations to use more than one CPU in a single machine.

These computers use theASCII character set (see ASCII). In addition, they define printed representations for all character codes from 0 to 255.

Figure 135 shows the printable part of the special character set. Under DOS or at a Windows command prompt, these characters are typed by holding down the Alt key and typing the appropriate number on the numeric keypad at the right side of the keyboard. For example, to type a shaded block, hold down Alt, type 178, and then release Alt.

high-performance desktop computers manufactured by Sun Microsystems of Mountain View, California. Most are marketed as single-user systems although each can support more than one user. All run Solaris (SunOS), a proprietary version of UNIX based on System V and incorporating some BSD features. Current Sun workstations are descendants of the Sun-4, which introduced the SPARC CPU; earlier products used Motorola 68000 and Intel 386 processors.

a family of high-performance 32- and 64-bit microprocessors developed jointly by IBM, Motorola, and Apple, to compete with the Intel microprocessors and Microsoft software that presently dominate the personal computer market. The successive models of the PowerPC chip are called G1, G2, G3, and so on.

Introduced in 1994, PowerPC processors are specially designed to emulate other kinds of CPUs efficiently. Thus a PowerPC-based computer can run DOS and/or conventional Macintosh software by running a special program on the PowerPC that recognizes and executes the machine instructions of the 386 or 68030 CPU, respectively.

The first PowerPCs to reach the market were Macintoshes. So far, PowerPC chips are not used in Windows PCs.

a family of personal computers introduced by Apple in 1984; the first widely used computers with a graphical user interface, windowing, and a mouse. The Macintosh user interface was derived from that of Xerox workstations; it has been imitated by a number of other operating systems, including Microsoft Windows and OS/2 Presentation Manager.

The mechanisms for using windows, icons, and mouse menus are provided by the operating system, which means they look virtually the same in all programs. Thus, anyone who knows how to use any Macintosh software package will also knowhowto perform similar operations in any other software package. Macintosh hardware is simple to set up because of Apple's early commitment to widely recognized standards such as PostScript, PDF, and SCSI. Macintoshes have always been on the forefront of practical computer graphics and related technology (for example, TrueType scalable fonts and QuickTime video), thus making them the preferred platform for the commercial arts.

Although the selection of available software is smaller than with PCs, Apple maintains a loyal and vocal following for the Macintosh. The computers perform well and the Mac user community is close-knit. This may be one reason Macintosh computers are not as plagued with viruses as the Windows community.

Apple currently offers a variety of Macintosh computers, giving their customers a wide variety of solutions for their computing needs. There are two basic lines of laptops: iBooks and Powerbooks (student versus professional models, respectively). As for desktop-style computers, Apple offers a traditional high-end line of computers calledPower Macs, but also offers the iMac, eMac, and Mac mini. The iMac is a very elegantly designed multi-use computer. eMacs were designed as a lower-cost option to the iMac, but are adequate for most computing tasks. The Mac mini is very small and easily transported. It can quickly hook up to any available monitor, mouse, and keyboard. The Mac mini is ideal for PC-users who also need access to a Macintosh computer.

The current version of the Macintosh operating system is macos x (read "ten," not "x").

For Macintosh serial port pinouts, see RS-232.

a CPU design with a small number of machine language instructions, each of which can be executed very quickly. The Sun Sparcstation and the PowerPC are examples of RISC computers. The opposite of RISC is CISC.

RISC architecture was developed for speed.A RISC computer can execute each instruction faster because there are fewer instructions to choose between, and thus less time is taken up identifying each instruction.

RISC and CISC computers can run the same kinds of software; the only difference is in what the software looks like in machine code. CISC is faster than RISC if memory access is relatively slow; the RISC machine has to fetch more instructions from memory than the CISC machine to do the same work. RISC is faster than CISC if memory access is very fast.