25 Jul
2014
25 Jul
'14
5:04 a.m.
From: Eric Smith <spacewar at gmail.com>
Date: Thu, 24 Jul 2014 20:22:30 -0600
Subject: microcode store (was Re: Looking to get into a Mini Computer...)
Early on, it was very expensive to use fast RAM chips for a microcode
store, so DEC used bipolar PROMs except on relatively high-priced
machines (e.g., KL10 and KS10), and if serious bugs were found, the
microcode PROMs had to be replaced.
The PDP-9 uses transformers to store it's microcode.
You can change the microcode by changing the routing of the wires
through the transformers.
http://www.ricomputermuseum.org/Home/equipment/dec-pdp-9/pdp-9-restoration/…
--
Michael Thompson
