Re: [TUHS] Monitoring by loudspeaker (was: BTL pranks)

[Robert Clausecker <fuz@fuz.su>]

When the computer is in a tight endless loop, the accumulator takes the
same series of values every time it's in the loop.  Thus, instead of
white noise you get a sound whose frequency is the clock frequency of
the machine divided by the number of cycles spent by one loop iteration.

That's how you know that the machine is stuck in an endless loop: if it
was doing something useful, the values would change every iteration and
you would get white noise again.

Yours,
Robert C

On Sun, Jul 12, 2020 at 11:58:11AM +0000, Michael Kjörling wrote:
> (This should probably be on COFF because I don't think this has much
> to do with UNIX.)
> 
> 
> On 11 Jul 2020 22:22 -0400, from doug@cs.dartmouth.edu (Doug McIlroy):
> > a loudspeaker hooked to the low-order bit of the accumulator played
> > gentle white noise in the background. The noise would turn into a
> > shriek when the computer got into a tight loop,
> 
> How did that work? I can see how tying the low-order bit of the
> accumulator to a loudspeaker would generate white noise as the
> computer is doing work; but I fail to see how doing so would even
> somewhat reliably generate a shrieking sound when the computer is in a
> tight loop. Please, enlighten me. :-)
> 
> -- 
> Michael Kjörling • https://michael.kjorling.se • michael@kjorling.se
>  “Remember when, on the Internet, nobody cared that you were a dog?”
> 

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