FPGA VAX update, now DIY TTL computers

Chuck Guzis cclist at sydex.com
Wed Nov 9 11:37:02 CST 2005


On 11/9/2005 at 11:49 AM Allison wrote:

>True for later generations.  However CDC6000 was more specialized 
>packaging where the PDP6 was a whole lot of flipchips and limited 
>specialized packaging.

Automated wire-wrapping is less expensive than other methods, but doesn't
give one the leve of control that other methods afford.

It now seems incredible on what amounts to a 10 MHz mainframe, but wire
length was a big part of the CDC 6600 design puzzle.  I recall a friend
telling me that his first assignment on his job at CDC was to take Cray's
6600 prototype and measure each coil of twisted pair to which had been
attached a tag that said "tune" in preparation for actually manufacturing
the thing.

 The old 6000-series taper-pin backplanes were a deep maze of wiring
hanging here and there and the nanosecond-per-foot rule was an important
part of the 6600 design.  CDC continued to use taper-pin style backplanes
long after other firms were using machine-wrapped backplanes, mostly, I
suspect because of the ability to optimize propogation delays--and still
retain the use of standardized "cordwood" logic modules.

Cheers,
Chuck





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