Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!necntc!linus!alliant!cantrell
From: cantrell@Alliant.COM (Paul Cantrell)
Newsgroups: comp.arch
Subject: Re: Cycle stretching
Message-ID: <1268@alliant.Alliant.COM>
Date: 23 Feb 88 16:33:08 GMT
References: <8802162251.AA20090@decwrl.dec.com> <3297@psuvax1.psu.edu>
Reply-To: cantrell@alliant.UUCP (Paul Cantrell)
Organization: Alliant Computer Systems, Littleton, MA
Lines: 24

In article <3297@psuvax1.psu.edu> przemek@gondor.cs.psu.edu (Przemyslaw Klosowski) writes:
>Hey, I saw an old PDP (was it 8?) with a knob on the front panel, regulating
>the clock frequency! you are pressed for time? turn it clockwise! (probably
>at the expense of the error rate). I personally would rather implement it as
>a foot operated lever under the operator console...   :^)
>				przemek@psuvaxg.bitnet
>				psuvax1!gondor!przemek


This was almost certainly a KA-10 processor, part of a DECSystem-10
computer system. The knob is used during debugging (of hardware or
software) to control the speed of single-step operation, not the
speed during normal operation. This was actually pretty nice if you
were debugging a problem with the operating system. You could place
the system in single step mode, crank the knob around to get desired
speed of single step, and watch the lights on the processor and memory
until you saw the condition you were looking for.

The KA-10 was indeed an asynchronous machine (I always heard it referred
to as a 'race' machine). The machine would run at different rates
depending on environmental conditions, which memory things were being
accessed from, etc. Different machines would run at different rates
from each other. It made it difficult to do good benchmarks...

					PC