Designing the first microprossor

We now routinely buy personal computers in which microprocessors with millions of transistors perform at gigahertz speeds, so it is easy to forget that the first microprocessor was not a simple or obvious choice to produce. At the time it was being contemplated, metal oxide semiconductor (MOS) technology was still quite new, and integrated circuits themselves had existed less than a decade. While MOS circuits with a thousand transistors were being manufactured, the economics of integrated circuits of that day limited how far the technology could be pushed. A 2-in-diameter silicon wafer, costing perhaps US$50 to process, might have a 10% yield for a 0.02-in
²
die. If we pushed the die size higher, there would be fewer potential die per wafer, and yield would fall precipitously. Table 1 shows how the die cost might vary with die size.