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Sunday, May 9, 2021

TRACKING WITH CLOSEUPS: HP 9825 Repair Part 7: How Dynamic RAM Works (or Doesn't)

In the next installment of the “everything is broken” saga, the focus moves on to the random access memory (RAM) of the Hewlett-Packard 9825 laboratory computer. The refresh circuitry appears not to be working, which causes the system to rapidly forget what's been stored. What's refresh? Perhaps a deep dive into the history and technology of dynamic RAM will refresh your memory!

The HP 9825 uses the 4116 dynamic RAM chip, which brought back…memories…as I designed a 64 Kb memory board in 1979 using this same iconic chip.

Posted at May 9, 2021 11:41