microcoding a PC into a PDP-11 (was: RE: Classic Computers v s. Classic Computing) - test-drb@ccmp.vtda.org

19 Sep 2001

Bill Pechter wrote:
...
  Actually much of the 11/780 microcode is in rom.
 The stuff loaded from RX01 is mostly bug fixes to the rom code.
 The patches went into the Writeable Control Store board. 
The VAX-11/750 did the same thing (IIRC the 
first microcode patch required a large number 
of roms to be changed by field service ... 
the control store was redesigned to allow
patchable code a-la 780).

...
  The 11/785 went to completely RAM loaded microcode.
 The 11/780 did have an optional second User Writeable Control Store
 board. 
In one or other of the DTJ articles, the
development of the MicroVAX II is described.
They used the VAX-11/730 with new microcode 
to simulate a MicroVAX II: the 11/730
was *completely* soft.

Antonio