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S-100 bus

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S-100 or IEEE696-1983 (withdrawn), was an early computer bus designed in 1974 as a part of the Altair 8800, generally considered today to be the first personal computer (or at least the first "microcomputer", insofar as it was designed for hobbyists rather than the general public). The S-100 bus was the first industry standard bus for the microcomputer industry. S-100 computers, consisting of processor and peripheral cards, were produced by a number of manufacturers. The S-100 bus formed the basis for homebrew computers whose builders (e.g., the Homebrew Computer Club) implemented drivers for CP/M and MP/M. These S-100 microcomputers ran the gamut from hobbyist toy to small business workstation and were the zenith of the microcomputer world until the advent of the IBM PC (which some of them outperformed).


The S-100 bus essentially consisted of the pins of the Intel 8080 run out onto the backplane. One early, unanticipated shortcoming was various power lines of differing voltages being located next to each other, resulting in easy shorting. This was addressed in later systems. The system included two unidirectional 8-bit data buses, but only a single bidirectional 16-bit address bus. Power supplies on the bus were unregulated +8 V and ±18 V, designed to be regulated on the cards to +5 V (used by TTL) and ±12 V (typically used on RS-232 lines or disk drive motors).

Examples of systems using the S-100 busEdit

  • IMSAI 8080
  • MITS Altair 8800

Examples of S-100 cardsEdit

Main article: List of S-100 cards
  • Cromemco ZPU
  • CompuPro 68K CPU
  • MITS

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