CDC disk drives (was Re: what IBM system is this?)
paulkoning at comcast.net
Thu Jul 9 08:49:24 CDT 2015
> On Jul 9, 2015, at 9:27 AM, P Gebhardt <p.gebhardt at ymail.com> wrote:
>> I remember encountering them mostly as replacements for the terrible 821
>> drives, which had the appearance of an 808, but substantially increased
>> capacity. I don't think any 821s were ever installed at a customer's
>> site, however--I saw the lot of them that we had falling to the CE
>> They were replaced by banks of 844s--lots of them. I think one site had
>> well over 100 installed, all hooked together with a MAC on at least 2
>> Cyber 74s.
> Wow, more than hundred of these CDC drives??? This must have been a massive
> installation! I didn't know so many disk drives could be combined with
> Cyber systems. Thanks for the insights!
> I was already amazed by pictures provided by the University of Auckland:
> It doesn't say, though, where this picture was taken.
Wow. It isn’t clear how many systems are behind those drives.
And I thought CERL (University of Illinois PLATO) was a big setup. When I was there (1975-1978) it had, I believe, about 20 844 drives. Those were all connected to a single 7054 (via extenders of course, which aren’t well documented in the manuals I have seen) and from there to a dual mainframe setup (Cyber 73 and CDC 6500). Both mainframes would do I/O, and on each there were two PPUs involved in the I/O to allow 1:1 interlace on 70-series channels. This setup seriously exercised the drive reservation logic.
I ran into a controlware bug there, trying to use the Deadstart function (03uu). It runs a sequence of conventional operations internally in the 7054, but as supplied it did not correctly handle a drive interlock status and would get things wedged up. That wasn’t hard to fix; it gave me my one exposure to the controlware code, which is why I have a copy of it, though unfortunately not a copy of the manual.
In theory, a 7054 with extenders can support 64 drives, since the unit number is a 6-bit value. And also, again in theory, you could hook up multiple 7054s if you need more drives than that. So well over a 100, accessible to a single system, is at least theoretically possible.
Chuck, what (in this context) is a “MAC”?
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