IBM PC

(computer)International Business Machines Personal Computer.

IBM PCs and compatible models from other vendors are the mostwidely used computer systems in the world. They are typicallysingle user personal computers, although they have beenadapted into multi-user models for special applications.

Note: "IBM PC" is used in this dictionary to denote IBM andcompatible personal computers, and to distinguish these fromother personal computers, though the phrase "PC" is oftenused elsewhere, by those who know no better, to mean "IBM PCor compatible".

There are hundreds of models of IBM compatible computers.They are based on Intel's microprocessors: Intel 8086,Intel 8088, Intel 80286, Intel 80386, Intel 486 orPentium. The models of IBM's first-generation PersonalComputer (PC) series have names: IBM PC, IBM PC XT, IBM PC AT, Convertible and Portable. The models of its secondgeneration, the Personal System/2 (PS/2), are known by modelnumber: Model 25, Model 30. Within each series, the modelsare also commonly referenced by their CPU clock rate.

All IBM personal computers are software compatible with eachother in general, but not every program will work in everymachine. Some programs are time sensitive to a particularspeed class. Older programs will not take advantage of newerhigher-resolution display standards.

The speed of the CPU (microprocessor) is the mostsignificant factor in machine performance. It is determinedby its clock rate and the number of bits it can processinternally. It is also determined by the number of bits ittransfers across its data bus. The second major performancefactor is the speed of the hard disk.

CAD and other graphics-intensive application programs canbe sped up with the addition of a mathematics coprocessor, achip which plugs into a special socket available in almost allmachines.

Intel 8086 and Intel 8088-based PCs require EMS(expanded memory) boards to work with more than one megabyteof memory. All these machines run under MS-DOS. Theoriginal IBM PC AT used an Intel 80286 processor which canaccess up to 16 megabytes of memory (though standard MS-DOSapplications cannot use more than one megabyte without EMS).Intel 80286-based computers running under OS/2 can workwith the maximum memory.

Although IBM sells printers for PCs, most printers will workwith them. As with display hardware, the software vendor mustsupport a wide variety of printers. Each program must beinstalled with the appropriate printer driver.

The original 1981 IBM PC's keyboard was severely criticised bytypists for its non-standard placement of the return and leftshift keys. In 1984, IBM corrected this on its AT keyboard,but shortened the backspace key, making it harder to reach.In 1987, it introduced its Enhanced keyboard, which relocatedall the function keys and placed the control key in an awkwardlocation for touch typists. The escape key was relocated tothe opposite side of the keyboard. By relocating the functionkeys, IBM made it impossible for software vendors to use themintelligently. What's easy to reach on one keyboard isdifficult on the other, and vice versa. To the touch typist,these deficiencies are maddening.

An "IBM PC compatible" may have a keyboard which does notrecognize every key combination a true IBM PC does,e.g. shifted cursor keys. In addition, the "compatible"vendors sometimes use proprietary keyboard interfaces,preventing you from replacing the keyboard.

The 1981 PC had 360K floppy disks. In 1984, IBM introducedthe 1.2 megabyte floppy disk along with its AT model.Although often used as backup storage, the high densityfloppy is not often used for interchangeability. In 1986, IBMintroduced the 720K 3.5" microfloppy disk on its Convertiblelaptop computer. It introduced the 1.44 megabyte doubledensity version with the PS/2 line. These disk drives can beadded to existing PCs.

Fixed, non-removable, hard disks for IBM compatibles areavailable with storage capacities from 20 to over 600megabytes. If a hard disk is added that is not compatiblewith the existing disk controller, a new controller boardmust be plugged in. However, one disk's internal standarddoes not conflict with another, since all programs and datamust be copied onto it to begin with. Removable hard disksthat hold at least 20 megabytes are also available.

When a new peripheral device, such as a monitor orscanner, is added to an IBM compatible, a corresponding, newcontroller board must be plugged into an expansion slot (inthe bus) in order to electronically control its operation.The PC and XT had eight-bit busses; the AT had a 16-bit bus.16-bit boards will not fit into 8-bit slots, but 8-bit boardswill fit into 16-bit slots. Intel 80286 and Intel 80386computers provide both 8-bit and 16-bit slots, while the 386salso have proprietary 32-bit memory slots. The bus inhigh-end models of the PS/2 line is called "Micro Channel".EISA is a non-IBM rival to Micro Channel.

The original IBM PC came with BASIC in ROM. Later, Basicand BasicA were distributed on floppy but ran and referencedroutines in ROM.

IBM PC and PS/2 models

PC range

Intro CPU FeaturesPC Aug 1981 8088 Floppy disk systemXT Mar 1983 8088 Slow hard diskXT/370 Oct 1983 8088 IBM 370 mainframe emulation3270 PC Oct 1983 8088 with 3270 terminal emulationPCjr Nov 1983 8088 Floppy-based home computerPC Portable Feb 1984 8088 Floppy-based portableAT Aug 1984 286 Medium-speed hard diskConvertible Apr 1986 8088 Microfloppy laptop portableXT 286 Sep 1986 286 Slow hard disk

PS/2 range

Intro CPU FeaturesModel 1987-08-25 8086 PC bus (limited expansion)Model 1987-04-30 8086 PC busModel 30 1988-09-286 286 PC busModel 1987-04-50 286 Micro Channel busModel 50Z Jun 1988 286 Faster Model 50Model 55 SX May 1989 386SX Micro Channel busModel 1987-04-60 286 Micro Channel busModel 1988-06-70 386 Desktop, Micro Channel busModel P1989-05-70 386 Portable, Micro Channel busModel 1987-04-80 386 Tower, Micro Channel bus

IBM PC compatible specifications

CPU CPU Clock Bus Floppy Hardbus speed width RAM disk disk OSbit Mhz bit byte inch byte Mbyte

8088 16 4.8-9.5 8 1M* 5.25 360K 10-40 DOS3.5 720K3.5 1.44M

8086 16 6-12 16 1M* 20-60

286 16 6-25 16 1-8M* 5.25 360K 20-300 DOS5.25 1.2M OS/2

386 32 16-33 32 1-16M** 3.5 720K Unix3.5 1.44M 40-600

386SX 32 16-33 16 1-16M** 40-600

*Under DOS, RAM is expanded beyond 1M with EMS memory boards

**Under DOS, RAM is expanded beyond 1M with normal "extended"memory and a memory management program.

See also BIOS, display standard.

IBM PC

A PC made by IBM. In 1981, the first IBM PC was introduced with a colossal 16KB of RAM. However, the company was not that optimistic, projecting that 250,000 IBM PCs would sell in the first five years. In fact, three million were sold in that period, and the PC industry, first DOS and later Windows, would become the world's largest computer base.

Good Bye IBM PC
In 2004, IBM exited the desktop and laptop arena when it sold its personal computer division to Lenovo, a major Chinese PC manufacturer. IBM retained its x86-based server market with its System x series until 2014, when Lenovo also acquired the line. See System x.

Names and Numbers
IBM's first PCs had names such as PC, XT and AT, while its next-generation PS/2 line was given model numbers. For historical purposes, early IBM model designations are listed below. See PC, IBM-compatible PC, ThinkPad, IBM and Lenovo.

The Original IBM PC

This first model had two floppy disks and 16KB of RAM. Today, a smartphone has 150,000 times as much memory and more. (Image courtesy of IBM.)

IBM PS/2 Model 50

The PS/2 introduced the Micro Channel bus, VGA graphics and the 3.5" floppy disk. See IBM PS/2. (Image courtesy of IBM.)

IBM ThinkPad

Very popular, IBM's ThinkPads introduced novel features such as the pointing stick and Butterfly keyboard. This model 755CD came out in 1994. See ThinkPad. (Image courtesy of IBM.)

FIRST GENERATION - IBM PCYearModel Intro. CPU Features PC (#1) 1981 8088 floppy disk XT 1983 8088 slow HD XT 286 1986 286 slow HD XT/370 1983 8088 370 emulation AT 1984 286 hard disk 3270 PC 1983 8088 3270 emulation PCjr 1983 8088 floppy home use PC Portable 1984 8088 floppy portable Convertible 1986 8088 floppy laptop SECOND GENERATION - IBM PS/2 Unless otherwise noted, models used the Micro Channel bus. YearModel Intro. CPU Features 25 1987 8086, PC bus 30 1987 8086, PC bus 30-286 1988 286, ISA bus 35 LS 1991 386SX, ISA, diskless 35 SX 1991 386SX, ISA L40 SX 1991 386SX, ISA, laptop 40 SX 1991 386SX, ISA N45 SL 386SL notebook 50 1987 286 50 Z 1988 286, faster 50 N51 SX 1992 386SX, notebook N51 SLC 1992 386SLC, notebook 55 SX 1989 386SX 55 LS 1990 386SX, diskless 56 SLC 1992 386SLC 56 SX 1992 386SX, upgradable 57 SLC 1992 386SLC 57 SX 1991 386SX, 2.88MB floppy CL57 SX 1992 386SX, notebook 60 1987 286 65 1990 386SX 70 1988 386 70 486 1989 486 P70 1989 386 portable P75 486 1990 486 portable, 22 lbs. 76 1994 486SX & DX, OS/2, SCSI 76i 1994 486SX, OS/2, IDE drive 77 1994 DX4, OS/2, SCSI, ECC RAM 77i 1994 DX4, OS/2, IDE, ECC RAM 80 1987 386, tower 90 1990 486, XGA, SCSI 90 1992 486DX2/66 95 1990 486, tower 90 SX 1991 486SX 95 SX 1991 486SX, tower