IBM 4331 Mainframe

dave.g4ugm at dave.g4ugm at
Mon May 1 13:16:45 CDT 2017

No, these were very much Air Cooled. IBM's advertising implied they could be
run in a normal office environment, e.g. as here:-


but in practice that layout would not work, clearance was required round all
sides as can be seen from the Physical Planning Manual which is available


One issue with these machines was that whilst they were (and still are I
guess) S/370 compatible, in some ways they were perhaps at the time not
considered "Mainframes" by the owners of real S/370 machines.


This was because System/370 I/O is normally managed by a "Channel Program"
which is executed by a "channel processor" and on the bigger boxes this was
a separate "CPU"

But on the 4331, 41 and 61 (but not 81) the main CPU was also used to
execute the channel programs, so whilst the CPU was 3x faster than a
370/115, under heavy i/I it would slow down as it was diverted to running
the channel programs. 

There is a whole chapter on this in:-


starting at page 12. You may also read this note:-
cpu#hit> &ft=MEMO&args=4331+channel+cpu#hit


and this
cpu#47> &ft=MEMO&args=4331+channel+cpu#47


about the problems that were had with this CPU.


Dave Wade


From: dwight [mailto:dkelvey at] 
Sent: 01 May 2017 17:54
To: dave.g4ugm at; General Discussion: On-Topic and Off-Topic Posts
<cctalk at>
Subject: Re: IBM 4331 Mainframe


Aren't these water cooled?

I seem to remember hoses.




From: cctalk <cctalk-bounces at
<mailto:cctalk-bounces at> > on behalf of Dave Wade G4UGM via
cctalk <cctalk at <mailto:cctalk at> >
Sent: Monday, May 1, 2017 9:48:52 AM
To: 'Guy Sotomayor Jr'; 'General Discussion: On-Topic and Off-Topic Posts'
Subject: RE: IBM 4331 Mainframe 


> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at] On Behalf Of Guy
> Sotomayor Jr via cctalk
> Sent: 01 May 2017 05:39
> To: General Discussion: On-Topic and Off-Topic Posts
> <cctalk at <mailto:cctalk at> >
> Subject: IBM 4331 Mainframe
> Just to let folks know that I finally moved the IBM 4331 Mainframe this
> weekend from where it was currently stored to my shop.  Pictures are here:
> <>
> As can be seen in the pictures, it filled a 26' box truck that I had
rented for
> this purpose.
> Right now I just have it placed somewhat in my shop.  Some early tasks
> be:
>    * I have to verify that I have everything.  Even if I missed some
items, they
> won't be
>      scrapped.  I just need to go over what is currently in my shop and
> that I didn't
>      leave anything behind.  I'm mostly worried about cables at this
>   * I have to figure out some way to produce enough "clean" 3-phase power
> to run the
>     peripherals (the CPU is 220v single phase) as I only have 220v single
> coming
>     into my shop.
> Starting to power it up will probably be a while yet.  ;-)

Yes I remember having a gentle discussion with the University of Salford
electricians, who wanted to know why I wanted 2 x 100amp feeds for the room
into which the 4361 (I think it was a 4361, might have been a 4331 or 4341)
was placed. I don't think we ever loaded them at 100amps but that was what
IBM required. One was for the AirCon and the other for the CPU. If I
remember properly those disks are the truculent ones. Assuming you have
AirCon they need to sit for several hours to acclimatise. 

> TTFN - Guy


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