🚀 go-pugleaf

mslater@cup.portal.com (Michael Z Slater) writes:
> The bug 
> Compaq referred to was in the FPU on the 486.  It occurs only under very
> specific and rare conditions...  An indication of
> how obscure the bus is is that the 486 passes all of Intel's test suites
> for the 387.

It might be obscure, but that's not a convincing argument.  How extensive
are the test suites for the 387? <<enter tired-aphorism mode>>  Testing can
only reveal the presence of bugs, not their absence.  <<exit tedium>>

A better measure of the problem is what it takes to avoid triggering it.
What's the cost in software to dodge the problem?  Actually, the 486 is
early enough in its lifetime that hopefully the bug can be banished by
replacing chips instead of hacking around it.

The multiply bug in the 386 is an instructive example here...it was a
relatively rare problem, and went a fair while without being known, yet the
effect was such that you couldn't reasonably use the bugged processors as
32-bit CPUs.
-- 
Dick Dunn     rcd@ico.isc.com    uucp: {ncar,nbires}!ico!rcd     (303)449-2870
   ...Worst-case analysis must never begin with "No one would ever want..."