Booting an IBM MP 3000 S/390 System

Dave G4UGM dave.g4ugm at
Thu Aug 6 09:59:51 CDT 2015

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at] On Behalf Of Al Kossow
> Sent: 06 August 2015 15:34
> To: cctalk at
> Subject: Re: Booting an IBM MP 3000 S/390 System
> On 8/6/15 6:16 AM, geneb wrote:
> > 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.

On a "normal" 360/370/390/Z there are multiple independent I/O processors,
called Channels. When you hit the IPL button it is one of the i/o processors
that actually loads the OS.
On an MP3000 the PC does some of the I/O work so it may be needed to IPL.

Most IBM Mainframes from 370 onwards have control processors to manage the
main CPU. Some even have smaller mainframes, so one has a 43xx box running
VM/CMS as the control box...
I believe that Gene Amdahl patented the use of a control processor and IBM
paid him licence fees for every Mainframe with a control processor.
Of course IBM owned the patents on Virtual Memory so Gene had to pay IBM to
use those....

> Apple ended up putting a small TI microcontroller in the G5 because it
> couldn't boot on its own. There was a bunch of volatile state you had to
> up before it would fetch its first instruction.

Lots of newer servers have some sort of control processor. I am used to IBM
"X" series which have a control CPU, and on payment of the appropriate
licence fee, you can enable remote console support which provides a Java app
which can be used to boot the server, power the main CPU up and down, and
even map a remove floppy/CD/DVD so you can remotely install an OS. Before
anyone asks it has a separate RJ45 jack. As long ago as 2000 I remember
Compaq having a RIB  board which did the same. I think it is now standard..


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