IBM PC
<computer> International Business Machines Personal Computer.
IBM PCs and compatible models from other vendors are the most widely used computer systems in the world.
They are typically single user personal computers, although they have been adapted into multi-user models for special applications.
Note: "IBM PC" is used in this dictionary to denote IBM and compatible personal computers, and to distinguish these from other personal computers, though the phrase "PC" is often used elsewhere, by those who know no better, to mean "IBM PC or 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 or
Pentium.
The models of IBM's first-generation Personal Computer (PC) series have names: IBM PC,
IBM PC XT,
IBM PC AT, Convertible and Portable.
The models of its second generation, the Personal System/2 (
PS/2), are known by model number: Model 25, Model 30.
Within each series, the models are also commonly referenced by their
CPU clock rate.
All IBM personal computers are software compatible with each other in general, but not every program will work in every machine.
Some programs are time sensitive to a particular speed class.
Older programs will not take advantage of newer higher-resolution
display standards.
The speed of the
CPU (
microprocessor) is the most significant factor in machine performance.
It is determined by its
clock rate and the number of bits it can process internally.
It is also determined by the number of bits it transfers across its
data bus.
The second major performance factor is the speed of the
hard disk.
CAD and other graphics-intensive application programs can be sped up with the addition of a mathematics
coprocessor, a chip which plugs into a special socket available in almost all machines.
Intel 8086 and
Intel 8088-based PCs require
EMS (expanded memory) boards to work with more than one megabyte of memory.
All these machines run under
MS-DOS.
The original
IBM PC AT used an
Intel 80286 processor which can access up to 16 megabytes of memory (though standard
MS-DOS applications cannot use more than one megabyte without
EMS).
Intel 80286-based computers running under
OS/2 can work with the maximum memory.
Although IBM sells printers for PCs, most printers will work with them.
As with display hardware, the software vendor must support a wide variety of printers.
Each program must be installed with the appropriate printer driver.
The original 1981 IBM PC's keyboard was severely criticised by typists for its non-standard placement of the return and left shift 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 relocated all the function keys and placed the control key in an awkward location for touch typists.
The escape key was relocated to the opposite side of the keyboard.
By relocating the function keys, IBM made it impossible for software vendors to use them intelligently.
What's easy to reach on one keyboard is difficult on the other, and vice versa.
To the touch typist, these deficiencies are maddening.
An "IBM PC compatible" may have a keyboard which does not recognize 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 introduced the 1.2 megabyte floppy disk along with its AT model. Although often used as
backup storage, the high density floppy is not often used for interchangeability.
In 1986, IBM introduced the 720K 3.5" microfloppy disk on its Convertible
laptop computer.
It introduced the 1.44 megabyte double density version with the PS/2 line.
These disk drives can be added to existing PCs.
Fixed, non-removable, hard disks for IBM compatibles are available with storage capacities from 20 to over 600 megabytes.
If a hard disk is added that is not compatible with the existing
disk controller, a new controller board must be plugged in.
However, one disk's internal standard does not conflict with another, since all programs and data must be copied onto it to begin with.
Removable hard disks that hold at least 20 megabytes are also available.
When a new peripheral device, such as a
monitor or
scanner, is added to an IBM compatible, a corresponding, new controller board must be plugged into an
expansion slot (in the 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 boards will fit into 16-bit slots.
Intel 80286 and
Intel 80386 computers provide both 8-bit and 16-bit slots, while the 386s also have proprietary 32-bit memory slots.
The bus in high-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, Basic and BasicA were distributed on floppy but ran and referenced routines in ROM.
IBM PC and PS/2 models
PC range
Intro
CPU
Features PC Aug 1981
8088
Floppy disk system XT Mar 1983
8088
Slow hard disk XT/370 Oct 1983
8088
IBM 370 mainframe emulation 3270 PC Oct 1983
8088
with 3270 terminal emulation PCjr Nov 1983
8088
Floppy-based home computer PC Portable Feb 1984
8088
Floppy-based portable AT Aug 1984
286
Medium-speed hard disk Convertible Apr 1986
8088
Microfloppy laptop portable XT 286 Sep 1986
286
Slow hard disk
PS/2 range
Intro
CPU
Features Model 1987-08-25
8086
PC bus (limited expansion) Model 1987-04-30
8086
PC bus Model 30 1988-09-286
286
PC bus Model 1987-04-50
286
Micro Channel bus Model 50Z Jun 1988
286
Faster Model 50 Model 55 SX May 1989
386SX
Micro Channel bus Model 1987-04-60
286
Micro Channel bus Model 1988-06-70
386
Desktop, Micro Channel bus Model P1989-05-70
386
Portable, Micro Channel bus Model 1987-04-80
386
Tower, Micro Channel bus
IBM PC compatible specifications
CPU
CPU
Clock
Bus
Floppy
Hard bus
speed
width
RAM
disk
disk
OS bit
Mhz
bit
byte
inch
byte
Mbyte
8088
16
4.8-9.5 8
1M*
5.25
360K
10-40
DOS 3.5
720K 3.5
1.44M
8086
16
6-12
16
1M*
20-60
286
16
6-25
16
1-8M*
5.25
360K
20-300
DOS 5.25
1.2M
OS/2
386
32
16-33
32
1-16M**
3.5
720K
Unix 3.5
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.
