Reproducing old machines with newer technology (Re: PDP-12 at the RICM)

[Chuck Guzis]

On 07/15/2015 10:35 AM, Paul Koning wrote:


> Then there was the very occasional early machine with no lights at
> all — the CDC 6000 series is the one I can think of.  But there you
> had the real time console status display, which was even better —
> updated just as fast but with a whole lot more information.

...and that counters Neil's assertion that lights were too expensive.
Cray didn't use lights, neither did CDC as well as other manufacturers.

What they used was (usually) a separate processor with diagnostic 
capabilities.

Lights and switches paled in comparison to what an intelligent 
diagnostic processor could do--you could see the state of I/O channels, 
the P-counter and the job to which it was attached, modify the status of 
just about anything in the system and--in some cases even tell the state 
of the cooling system.  Some allowed the operator to degrade system 
memory, allowing normal work to proceed using part of memory while 
performing diagnostic testing on the other part.

Lights are a quaint holdover from the 1950s and early 60s and really a 
cheap alternative to getting system information. The console on a360/195 
is an example of the technology carried to a ridiculous extreme.  The 
minicomputers of the 70s with their lights and switches being the last 
holdout, mostly because of cost.

--Chuck