IBM PC

IBM PC™ (Personal Computer), is a trademark of IBM. The predecessor of the current personal computers and progenitor of the IBM PC compatible hardware platform, it was introduced in August 1981. The original model was designated the IBM 5150. It was created by a team of 12 engineers and designers under the direction of Don Estridge of the IBM Entry Systems Division. The introduction of the PC changed the world of IBM in 1981.

Technology

Electronics

The main circuit board in an IBM PC is called the motherboard. This carries the CPU and memory, and has a bus with slots for expansion cards.

Related Topics:
Motherboard - CPU - Memory - Bus

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The bus used in the original PC became very popular, and was subsequently named ISA. It is in use to this day in computers for industrial use. Later, requirements for higher speed and more capacity forced the development of new versions. The VESA Local Bus allowed for a single, much faster 32-bit card slot for display cards, and the EISA architecture was developed as a backward compatible standard including 32-bit card slots, but it only sold well in high-end server systems. The lower-cost and more general PCI bus was introduced in 1994 and has now become ubiquitous.

Related Topics:
ISA - VESA Local Bus - EISA - PCI - 1994

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The motherboard is connected by cables to internal storage devices such as hard disks, floppy disks and CD-ROM drives. These tend to be made in standard sizes, such as 3.5" (90 mm) and 5.25" (133.4 mm) widths, with standard fixing holes. The case also contains a standard power supply unit (PSU) which is either an AT or ATX standard size.

Related Topics:
Hard disk - Floppy disk - CD-ROM - Power supply

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Intel 8086 and 8088-based PCs require EMS (expanded memory) boards to work with more than one megabyte of memory. The original IBM PC AT used an Intel 80286 processor which can access up to 16 megabytes of memory (though standard DOS applications cannot use more than one megabyte without using additional APIs. Intel 80286-based computers running under OS/2 can work with the maximum memory.

Related Topics:
Intel - 8086 - 8088 - EMS - Megabyte - 80286 - DOS - OS/2

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Keyboard

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.

Related Topics:
1981 - Keyboard - 1984 - 1987 - Enhanced keyboard - Touch typist

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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 used proprietary keyboard interfaces, preventing you from replacing the keyboard.

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See also: Keyboard layout

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Character set

The original IBM PC used the 7 bit ASCII alphabet as the basis, but in addition this was extended to an 8 bit somewhat haphazardly collected set of characters unique for the IBM PC. This set was not really suitable for international use, and soon a veritable cottage industry emerged providing variants of the original character set in various national variants. In IBM tradition, these variants were called code pages. These codings are now obsolete, being replaced by more well thought out schemes for character coding, like the ISO 8859-1 and Unicode.

Related Topics:
ASCII - Code page - ISO 8859-1 - Unicode

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This was the original IBM PC character set:

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Storage media

Technically, the standard storage medium for the original IBM PC model 5150 was a cassette port. It was virtually obsolete—even by 1981 standards—and very few (if any) IBM PCs left the factory without a floppy disk drive installed. The 1981 PC had one or two 180 kilobyte 5 1/4 inch single sided double density floppy disk drives; XT's generally had one double sided 360 kilobyte drive (next to their hard disk).

Related Topics:
1981 - Kilobyte - Floppy disk - Hard disk

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The first IBM PC that included a fixed, non-removable, hard disk was the XT. Hard disks for IBM compatibles soon became available with very large storage capacities. If a hard disk was added that was not compatible with the existing disk controller, a new controller board had to be plugged in; some disks were integrated with their controller in a single expansion board.

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In 1984, IBM introduced the 1.2 megabyte dual sided floppy disk along with its AT model. Although often used as backup storage, the high density floppy was not often used for interchangeability. In 1986, IBM introduced the 720 kilobyte double density 3.5" microfloppy disk on its Convertible laptop computer. It introduced the 1.44 megabyte high density version with the PS/2 line. These disk drives could be added to existing older model PCs. In 1988 IBM introduced a drive for 2.88 megabyte "DSED" diskettes in its top-of-the-line models; it was an instant failure and is all but forgotten today (but survives as a possible "size" choice in disk-formatting utilities).

Related Topics:
Double density - High density - Disk-formatting

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Software

All IBM PCs includes a relatively small piece of software stored in ROM and used mainly for bootstrapping, called a BIOS. In addition, the original IBM PC came with BASIC in ROM (Cassette BASIC). Later, BASIC and BASICA were distributed on floppy disks but ran and referenced routines in the PC's ROM.

Related Topics:
ROM - Bootstrap - BIOS - BASIC - Cassette BASIC - BASICA

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