Booting an IBM MP 3000 S/390 System

[Chuck Guzis]

On 08/06/2015 07:33 AM, Al Kossow wrote:

> 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.

And really big iron almost always had some sort of maintenance control 
processor--some with their own mass storage.  Have a separate, simpler 
processor handle the management of a larger one made a lot of sense, 
particularly when it came to diagnostic activity.

Think Cray, CDC,...

--Chuck