"Carlini, Antonio" wrote:
> 
> > Gunther Schadow wrote:
> >
>         >(c) the VAX 11/750 also has an easy access for microcode hacks
>         >     as used by NetBSD.
> 
>         The original VAX-11/750 came with permament
>         microcode - an update required changing some
>         hige number of roms (I heard in the three figures
>         but I never checked myself). 
120 of them, in fact! The PCS used 30 much bigger proms. 
> Shortly afterward
>         an updated board was issued that allowed for
>         patchable microcode, via a boottime load.
>         There is a limit to how much patching you can do
>         without swapping ROMs. Enough for DEC to
>         issue fixes (last I know of is 104 with VMS V5.0 but
>         I stopped using a 750 shortly afterwards) but
>         possibly not enough for you to implement
>         Java primitives!
The PCS came in three variants. One had just the standard 1k bank
of RAM for microcode patches, but the other two came with one or
two more 1k RAM banks for user microcoding. As far as I remember, the 
only official use for this was extended precision floating point
microcode. 

I've always been interested in the possibilities of microcoding the
750, but it's really difficult to get enough information. The CPU
technical
description is a start, but it makes constant reference to the microcode
listing, which I've never been able to find a part number for. If
anybody
out there knows how I would go about getting a copy, I'd be very
interested
to hear from them!

James