CDC disk drives (was Re: what IBM system is this?)

Chuck Guzis cclist at
Thu Jul 9 11:44:06 CDT 2015

On 07/09/2015 06:49 AM, Paul Koning wrote:

> Chuck, what (in this context) is a “MAC”?

"Multiple Access Controller"--pretty much just a software-programmable 
switch.  At one time, was strictly a QSE--we used them extensively on 
4-Cyber configurations sharing 4MW of ECS and multiple peripherals.

The idea was that any CPU could get to any peripheral.  So a site with 4 
CPUs might be equipped with a couple of 512 printers; but any CPU could 
use any printer.

This extended to the disk drives, IIRC.  Mostly it involved an extra FCN 
instruction ahead of the usual code.   So one could take a stock SCOPE 
deadstart, and just key in the FCN from DSD to get to an available 
printer not the default.   Sometimes COMSOURCE would run on one of the 
systems, while our project was using another in the same configuration. 
  It annoyed the COMSOURCE operators no end when their peripherals would 
be "stolen" by our system.

But don't get me started on COMSOURCE...

On our big setups, the 844s had their own filesystem--keeping over 100 
drives online (not as PF drives) using the usual RBR/RBT scheme would 
have eaten up a lot of CM.  In our case, we used them for an indexed 
database, so the database itself had the block linking information 
embedded, so all that was needed was a simple bitmap to indicate used 


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