Xref: utzoo comp.arch:12172 comp.sys.intel:984 comp.sys.ibm.pc:37438 Path: utzoo!utgpu!utstat!jarvis.csri.toronto.edu!mailrus!ncar!ico!vail!rcd From: rcd@ico.isc.com (Dick Dunn) Newsgroups: comp.arch,comp.sys.intel,comp.sys.ibm.pc Subject: Re: Compaq finds problem with chip Summary: Obscurity is subjective Message-ID: <1989Nov2.074808.2913@ico.isc.com> Date: 2 Nov 89 07:48:08 GMT References: <2719@ganymede.inmos.co.uk> <2725@ganymede.inmos.co.uk> <23548@cup.portal.com> Organization: Interactive Systems Corporation Lines: 23 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? <> Testing can only reveal the presence of bugs, not their absence. <> 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..."