EEVblog #904 – Hewlett Packard HP85 Professional Computer

1979, a screaming 613KHz clock, killer graphics, and it’s a Hewlett Packard, it doesn’t get much better than this!
Dave powers up the the classic HP85 Scientific / Engineering Professional Personal Computer and has a play around.
Forum HERE

Teardown VIDEO
Repair VIDEO
User Manual
Pocket Guide

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    • Chris Lott

      Early in the video you post some text saying HP made their own chip for accuracy reasons because other computers operated in binary, whereas HP calculators/computers operated in decimal arithmetic. Well, technically speaking most microprocessors have/had the ability to perform BCD arithmetic, at least all the ones I have worked on in the past. It is cumbersome compared to performing binary arithmetic, basically you used a binary add instruction on a packed decimal byte, then issued a “decimal adjust” instruction. I can certainly see how a custom chip designed for decimal operations from the ground up would be quicker and more efficient. This whole notion came to my attention as a young engineer in the mid-80s, when our company policy was to use Borland’s Turbo Pascal compiler. I realized Borland provided two math libraries, one for binary and one for decimal, dug a bit deeper and discovered these BCD instructions in the x86 processors and x87 FPUs of the day.

      Incidentally, I remember many years back when the stock exchange in the USA switched from power-of-two fractional pricing to decimal – the primary reason offered was that because of digital computers, fractional pricing resulted in round-off errors. This drove me crazy, because the truth is the opposite – the computer’s natural format is precisely those power-of-two fractions.

      Great teardown.


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