Modifying microcode

[Eric Smith]

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

> 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.