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Ed Roberts decided that a change was needed and he decided to build a computer kit based on the new Intel 8080 chip. There were already a small number of computer kits available and the personal computer industry was very definitely trying to get out. Scelbi Computer Consultants had already introduced possibly the very first computer kit - the 8-H - but it was based on the under powered 8008 microprocessor and was more like an advanced controller than a computer.
Roberts had decided to go for something more like a real computer and based his design on the then new Intel 8080. The 8080 was an eight-bit device and the start of the family of Intel processors that led up to today's mulicore Pentium range. Even so by today's standards the chip was fairly feeble - 64KByte addressing and a very limited instruction set. The design of the machine wasn't an easy project but perhaps the most important step was to decide that the price would be less than $400. This was a bold step given that the 8080 was selling for around $350 a piece. Roberts managed, some how, to persuade Intel to part with the chips for $75 each!
The hardware design that Roberts and his team of engineers finally came up with set the standard for the explosive development that were to follow. Much of the design was cooked up via phone conversations with his old school friend Eddie Curry. Later Curry would become executive vice president. Rather than attempt to build the whole thing on one printed circuit board MITS used a modular design. The CPU was assembled on one card, the memory on another and the interface on yet another. The whole lot was connected together by motherboard with four sockets.
The CPU card
The bus that Ed Roberts introduced would become famous as the S100 bus although it was little more than the basic control signals of the 8080 processor supplemented by a few necessary extras and 50 earth connections - making a total of 100 connections that give the bus its name. The case that the electronics were packed into was just a rectangular box but it did have the necessary array of flashing LEDs and key switches! At that time the popular conception of a computer involved banks of flashing lights and switches but the need for them in this case was far from cosmetic. The problem was that there were no suitable I/O devices for this early personal computer. The only way that it could be programmed was via the switches. You had to key in the binary code of each instruction in turn and when you ran your program the output was via the pattern of LEDs on the front panel. It is difficult to believe that keyboards and video displays were just too expensive - but they were!
When you are selling a dream for $500 you need a good name to make sure that your audience's imagination is captured. David Bunnell, a MITS technical writer, suggested calling the machine "Big Brother". It is probably a good job that his suggestion wasn't taken up!