Modifying microcode

Eric Smith spacewar at
Thu May 31 10:28:47 CDT 2018

On Wed, May 30, 2018, 20:26 Jon Elson via cctalk <cctalk at>

> The early 780 had most microcode in ROM, and had a small
> writable control store for special OS-required options and
> patches.  Later machines had more WCS, but I think they
> still had some non-writable control store.

The control stores of the 11/785, 8600, and 8650 were entirely WCS.
Probably the so-rare-as-to-be-almost-nonexistent 9000 series had entirely
WCS as well.

All other VAXen had (relatively) large ROM control store and tiny WCS or
patch store.

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