In this web content, the author explores the internal components and workings of an unusual HP chip called PHI (Processor-to-HP-IB Interface) from 1977. The chip is unique because it is formed on a base of sapphire instead of silicon, making it transparent. The author delves into the silicon-on-sapphire technology used in the chip, its advantages and disadvantages, and its applications in space and other industries. The author also examines the circuitry, logic gates, FIFOs, and address decoder within the chip. This chip is an example of a technology that didn’t become mainstream, as regular silicon chips proved to be more successful.
https://www.righto.com/2023/12/HP-silicon-on-sapphire-phi-chip.html