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From: spain@Alliant.COM (Dave Spain)
Newsgroups: comp.misc
Subject: Re: Looking for Computer Folklore
Message-ID: <2956@alliant.Alliant.COM>
Date: 3 Feb 89 23:54:59 GMT
References: <7143@pyr.gatech.EDU> <532@geovision.UUCP> <4575@tekgvs.GVS.TEK.COM> <1798@valhalla.ee.rochester.edu>
Reply-To: spain@alliant.Alliant.COM (Dave Spain)
Organization: Alliant Computer Systems, Littleton, MA
Lines: 20

>	Another unverified bit of folklore: I've heard several times that
>	the Vax 11/750 had a delay loop in the microcode, to insure that it
>	would run slower than the Vax 11/780.
>
>			Del Armstrong

I spent 3 years at DEC writing micro-code level diagnostics for the 11/750,
which often entailed thumbing through the micro-code listings to see how
certain things were done, and I cannot remember running into any delay loops.

There was a bit in the microword that extended one of the major clocks
to allow certain slower functions to complete. Perhaps this is what got
this folklore started.

However, the major machine cycle time was considerably slower for the 750 vs
the 780 (If memory serves, I believe this was 320ns vs 200ns, not counting
extended clocks and FPA operations), a limitation imposed by the technology
(i.e. those early 400-gate bipolar gate-arrays) and not by the microcode.

Dave Spain