The S -100 bus was an early computer bus, which was designed as part of the Altair 8800, which is now regarded as the first personal computer. The S -100 bus was the first bus, which was a kind of industry standard. S-100 computer processors and peripheral devices were manufactured in 1975 to approximately 1985 by several manufacturers.
During the design of the Altair was quickly realized that the hardware that was needed for a usable machine, would not be available in time to launch in January 1975. The designer, Ed Roberts, also had problems with the motherboard that simply took up too much space. To solve these problems, he packed the existing components in an enclosure with additional slots so that the missing hardware could be added later as soon as they became available. The main circuit board has been divided into four different maps with the CPU to a fifth. Then he was looking for an inexpensive source for connectors and tripped over a 100 - pinnigen edge connector ( edge connector ), which was the basis for the S-100 bus.
The most important feature of this bus is probably that it consists essentially of the pins of the Intel 8080, which are extended only to the board. In the design of the bus was not too much ( thinking ) invested work, so that it came to such disasters as several power lines with different voltages directly next to each other, resulting in a short circuit provoked outright. Another absurdity: The system included two unidirectional 8 -bit data buses, but only a bi-directional 16 -bit address bus. A bargain when buying power supplies meant that V on the bus 8 and 18 V were used as tensions on the cards by Verheizen of the surplus to the much more commonly used TTL level ( 5 V) or RS -232 ( 12 V) had to be turned down.
Despite these shortcomings, the S -100 bus developed from this point on the standard bus for professional personal computer, almost all were running under the operating system CP / M. The standard was so strong that many CPU designs have either been modified so that they looked like the 8080, or they were installed on so-called converter cards, which would allow them to operate in S-100 machines. Only the wide dissemination of the IBM PC and its clones, with their own bus system ( XT bus architecture ), put the S-100 bus to an end.
From the S-100 bus existed a number of variants of different manufacturers, but the bus was standardized in 1982 ( when his use already meet coming to an end ) as IEEE 696.