HP2100a VS HP2100s

From: Jay West <jwest_at_classiccmp.org>
Date: Mon Aug 23 08:10:18 2004

John wrote...
> Surely the 2100S has user-writeable microcode? The front panel
> says "Microprogrammable Systems Computer":

As a followup - I just found over the weekend something I wasn't aware of.
Apparently the 2100A/S isn't "entirely" microprogrammable. In order to
maintain full compatability with the earlier systems (2114/2115/2116), about
2/3 of the instruction set is microprogrammed (the base set of microcode in
module 0). The other 1/3 of the base instruction set is actually done in
hardware - mostly. This is because the few instructions that are built into
the hardware would take too long to execute in microcode. However, for those
hardware based instructions to execute, that circuitry needs to be enabled
via microcode instructions. Fascinating, I had no idea.


Jay West

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Received on Mon Aug 23 2004 - 08:10:18 BST

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