4 ms·
LOOP was a great instruction until Microsoft messed it up. If the instruction went fast enough, a timing loop in Windows got messed up, and Windows wouldn't boo
by souprock 6y ago
LOOP was a great instruction until Microsoft messed it up. If the instruction went fast enough, a timing loop in Windows got messed up, and Windows wouldn't boot. People would blame the CPU vendor for the bug, so LOOP was purposely made slow.
- andy_ppp 6y agoIntel do that with a lot of old instructions I.e. MMX and SSE instructions are really really fast on AMD but horrible on Intel. I guess this is to force people to upgrade to the latest and greatest AVX whatever.
- yvdriess 6y agoCitation needed? I've never encountered that, and used plenty of those. The main reason old instruction become slow is that the hardware implementation is replaced by a microcoded version.
- dogma1138 6y agoMMX these days costs extra instructions on both AMD and Intel CPUs. This has been the case since SSE and SSE2 were introduced and later AVX extensions. There quite possibly been a point in time where certain MMX instructions run faster on some AMD CPUs and required less uOps to achieve. https://agner.org/optimize/ https://agner.org/optimize/ This is a pretty good source for uOps and instruction cycles.
- YetAnotherNick 6y agoThis looks an interesting story that I tried to do Google it, but couldn't find any reliable source. Isn't it easy to do windows fix than processor hack? I could find some reasons though here https://stackoverflow.com/questions/35742570/why-is-the-loop-instruction-slow-couldnt-intel-have-implemented-it-efficiently https://stackoverflow.com/questions/35742570/why-is-the-loop...
- souprock 6y agoI recall that the affected OS was Windows 95. (could be 98) The first to hit the problem was AMD. Although not pre-internet, it nearly is, so finding info would be hard. People didn't get automatic updates from fast always-on connections. Lots of people had slow dial-up connections. For some people, even that wasn't an option, so an update would require physical media.
- kmm 6y agoI think this is the story referred to: http://www.os2museum.com/wp/those-win9x-crashes-on-fast-machines/ http://www.os2museum.com/wp/those-win9x-crashes-on-fast-mach...