2023-12-21 18:18:00
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21.12.2023 21:18, Sergey Surabekyants
In an HP computer released back in 1977, lovers of computer antiquities discovered a mysterious transparent chip. Further study of this chip showed that it is a silicon chip on a sapphire substrate. The purpose of the unusual processor turned out to be much more mundane than one might expect – the chip performed an auxiliary function in a floppy disk controller.
Image source: Ken Shirriff
Computer history researcher and chip reverse engineering enthusiast Ken Shirriff discovered an interesting chip while examining an antique HP computer. This chip wasn’t taken from some futuristic company experiment with a photonic supercomputer server, but was found in a modest floppy drive controller circuit board located between the HP Interface Bus (HP-IB) and the Z80 processor. The chip was responsible for processing the transmission protocol and data buffering.
A silicon-on-sapphire chip may seem a bit futuristic, but Shirriff said semiconductors have been made this way since at least 1963. A prime example of a silicon-on-sapphire chip is the RCA 1802 processor used on the Galileo space probe, which studied Jupiter and its moons.
Image source: NASA
Shirriff detailed some of the features of such chips, emphasizing that the sapphire substrate is an effective insulator for separating different areas of silicon. According to him, this design “reduces leakage between transistors, improving performance”. Moreover, sapphire’s insulating properties can prevent stray currents and protect once morest short circuits and radiation, hence its use in space electronics.
The researcher specifically noted that this chip is “silicon-on-sapphire” “interesting as an example of a future technology that hasn’t quite panned out.” In terms of their characteristics, such microcircuits were superior to conventional silicon chips, but the yield of usable microcircuits using silicon-on-sapphire technology from HP was only 9%. Technology development might take a different path if these transparent chips were mass produced with greater productivity and lower production costs.
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