Article 95 of comp.sys.cdc:
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From: Paul.C.Smith@cdc.com (Paul C. Smith)
Newsgroups: comp.sys.cdc
Subject: Re: Reminiscing About the Cyber 6600
Date: Wed, 14 May 1997 19:14:09 -0500
Organization: Control Data Systems, Inc.
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In article <jdykstra-1405971415140001@ndpam1a.dpark.nt.com>,
jdykstra@nortel.com (John Dykstra) wrote:
)
)It's also notable that these modules were HEAVY--the main body of the
)module is a thick metal plate.  This was probably partly for cooling
)purposes;  the modules were mounted on chassis that had chilled water
)flowing through them.  The CDC customer engineers had to be plumbers as
)well as technicians.

More like a refrigeration specialist, actually.  The coolant loop *within* 
the mainframe on these machines used Freon (R-12) rather than water.  The
machine *did* require an external supply of chilled water to cool the
Freon.
It wasn't until much later, in machines like the Cyber 990, that we used
water in a closed coolant loop inside the mainframe itself.  And the very
last Cyber models (the 960 and the 2000) were air-cooled.

Here at Arden Hills we've got big cooling towers out behind the facility, 
which used to run full blast all winter long generating chilled water to 
cool all the mainframes.  Nowadays we only use a couple of the towers to 
run the air conditioning, even on hot days...

Paul C. Smith
NOS Support
Control Data Systems, Inc.