CDC 6600 display character generation

[Jim Manley]

Using all of those gates to do brute-force logic for character vector
generation is pretty brilliant.  Edison was truly a genius because he
invented and sold the electric light so that people could stay up late at
night to listen to his phonograph invention that he also sold.  The
electric lights also eliminated the risk of coal tar condensing on the
phonograph cylinders from coal gas lights on the walls.

Seymour Cray was a genius because he observed that the fastest possible
circuit is a wire, and that if you use the same length of wire for each bit
in a word in cables between stages in a computer that you want to go as
fast as possible, all of the bits will arrive at the next stage at the same
time.  That was important for computers that took up entire rooms, with
circuit boards and racks far enough apart that upwards of a dozen
nanoseconds could elapse as bits passed from stage to stage.

IBM "solved" this synchronization problem in the 6600's contemporary, the
Model 3090 (Stretch), using delay lines to hold bits arriving on shorter
cables until bits arriving on longer cables could catch up.  The last thing
you want in a supercomputer is a component that has the word "delay" in it,
and by using equal-length wires for every bit in a word between stages, you
also reduce parts count.

That means that you reduce parts and assembly labor costs, replacement
parts costs, power and cooling costs (a very important function, back
then), system volume and weight (and therefore, structural costs), and the
costs of troubleshooting labor needed to identify which parts have failed
that didn't need to be there in the first place (or additional circuitry to
identify where faults occurred, adding yet-more of all of the above
expenses).

At the time, CDC had 39 employees, including Seymour and the janitor, while
IBM's engineering and technician head-count alone was upwards of 20,000.
The 6600s were the fastest computers in the world for over six years, and
would have held the record longer, except that CDC's own 7600s eclipsed
them.  He hired local women with experience doing mind-numbing, repetitive,
but precision tasks like knitting and needlepoint, to wire the
interconnects between boards on the Cray 1s and 2s.

However, they could gossip about who was seeing whom around town to while
away the hours, for which they were paid less than technicians, but more
than for any other work women could get back then.  I'll bet they made
fewer mistakes than alternative employees would have, too.  Seymour told
them how important their work was to the nation's defense, and they were
proud of it (many Crays were used on DoD projects for advances in pure
science, as well as engineering).

"Things should be as simple as possible, but no simpler." -- Albert
Einstein (talking about scientific education, but not a bad idea, in
general)


On Wed, Jun 6, 2018 at 3:26 PM, Paul Koning <paulkoning at comcast.net> wrote:

>
> The crazy thing about the 6000 series display controller is that it
> doesn't use tables at all.  The selection of what stroke step to produce
> for a given character and point in time is defined by a very large
> collection of gates.  The 170 controller does use table lookup (a ROM with
> the equivalent information).  I wonder why a ROM wasn't used in the 6000.
> Perhaps they couldn't find a cost-effective technology that's fast enough?
> Core rope would work just fine for this, but not at 100 ns cycle time.
>
>         paul
>