7 Aug
2015
7 Aug
'15
5:26 a.m.
As Al says, the microcode was dynamic and loaded from the boot console.
I remember our (Deluxe Coachlines, Australia, 1987-1990) VAX 8550s and 8820
had PRO based boot consoles.
When we had both 8550s failing with double CPU faults the DEC engineers
loaded new microcode onto the consoles to diagnose the problem.
On 6 August 2015 at 15:33, Al Kossow <aek at bitsavers.org> wrote:
On 8/6/15 6:16 AM, geneb wrote:
--
4.4 > 5.4
One thing I don't understand - why can't
the machine boot on its own?
Why would IBM design a computer that required another computer just to
boot it?
Main processor microcode is in RAM. Putting microcode in ram and having a
small computer load it was actually pretty common in the 70's and 80's in
larger systems since then you didn't have to manage the hassle of patching
microcode in ROM.
Apple ended up putting a small TI microcontroller in the G5 because it
also couldn't boot on its own. There was a bunch of volatile state you
had to set up before it would fetch its first instruction.