IBM Personal Computer

IBM’s 1981 Model 5150 microcomputer helped establish an open hardware architecture that became the basis for IBM PC compatibles.

Intel 8088: A 16-bit microprocessor with an 8-bit external data bus, introduced by Intel in 1979. The 5150’s CPU made its architecture compatible with inexpensive 8-bit peripheral components.
Expansion card: A circuit board installed in a computer slot to add functions or connect devices. Expansion cards gave 5150 owners ways to add memory, display, and communications hardware.
Don Estridge: An IBM engineer who led the team that developed the original IBM Personal Computer. Estridge’s team delivered the 5150 using a development process unusual for IBM.
Compaq Portable: A portable IBM PC-compatible computer released by Compaq in 1983. Compaq’s machine demonstrated that firms could reproduce IBM compatibility without IBM’s approval.
IBM PC BIOS: Firmware that initializes IBM PC hardware and provides low-level services to software. The BIOS let software interact with the 5150’s hardware through a common interface.
IBM PC DOS: The operating system IBM supplied for the original IBM PC, developed by Microsoft from 86-DOS. PC DOS provided the software environment that launched applications on the 5150.
Project Chess: IBM’s internal project to develop the original Personal Computer, begun in 1980. Project Chess produced the 5150 on a compressed schedule using outside suppliers.
Phoenix BIOS: A commercially licensed IBM PC-compatible BIOS developed through clean-room reverse engineering. Phoenix enabled compatible makers to use BIOS functionality without copying IBM’s code.
ISA bus: A parallel computer bus used to connect expansion cards to early IBM PC-compatible systems. The 5150’s expansion slots exposed a bus that third parties could build cards for.
Open architecture: A system design that makes interfaces and specifications available for independent implementation. IBM’s published technical information allowed outside firms to make compatible hardware.

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