CDC 6600 - Why so awesome?

Paul Koning paulkoning at
Tue Jun 21 19:12:17 CDT 2016

> On Jun 21, 2016, at 5:39 PM, Noel Chiappa <jnc at> wrote:
>> From: Swift Griggs
>> I see a lot of traffic about them on the list and I went out to
>> discover "why so cool?" 
> One word - 'crunch'. The 6600 especially, but also its successors (7600, etc)
> were _the_ number-crunching monsters of their day. 

Yes.  The 6600 was an amazing engineering accomplishment.  It had extremely fast memory for its day (under a microsecond access time, in 1964).  It could run several million instructions per second.  Floating point add in half a microsecond, multiply in one microsecond.

Lesser known things, like context switching ("exchange jump") in about 4 microseconds (!).  And divide was done two bits per clock tick rather than the usual one bit per tick; essentially it was doing long division base 4 rather than base 2 as is common.

Also a disk drive (6603) that was WAY faster than its peers because it recorded data in 12 bit words parallel rather than using a serial bit stream.  I believe something similar was also done in the Cray 1, but CDC had it a decade earlier.


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