Self modifying code, lambda calculus - Re: ENIAC programming

Johnny Billquist bqt at
Fri Sep 18 16:38:12 CDT 2015

On 2015-09-18 15:45, tony duell wrote:
>>> As far as I know, the VAX11/730 (There is one next to me waiting for me to have time
>>> to restore it) has the microcode entirely in RAM. Classic PERQs (3 in the next room) have
>> The PDP-11 console loads the microcode from disk then mostly just sits there
>> looking pretty whilst the VAX runs.
> The 11/780 has a PDP11 to load the microcode (I think) but the 11/730 makes do with an
> 8085. After booting I think that handles the console port still.

The VAX-11/78x had some microcode on a floppy. Not sure if it was 
required in order to run the machine, or if just a few select bits and 
pieces were on that floppy. It's been way too many years since I touched 
those machines. Maybe someone else will know?

The VAX-11/750 have the microcode in rom, but it has a system by which 
you can patch the microcode. There is some ram, but not enough to hold 
all the microcode. You you can "overwrite" selected addresses of the 
microcode, and this was/is used both by VMS, Ultrix and NetBSD to fix a 
few bugs in the machine.

The VAX-11/730 would have to have the microcode on TU58, as that is the 
console media. Quite possible that it actually do load the microcode 
from there at power up. I've heard that those machine were slow in so 
many ways... :-)

The VAX-86x0 machines have the microcode on the front-end RL02. All of 
it. You want a copy? :-)


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