Reply 20 of 148, by Phido
wrote:Quake doesnt need fast FPU, Quake needs pipelined one - ability to interleave instructions using zero cycle fxch register swaps. Afaik nothing x86 pre Intel Pentium did that, AMD caught up in late 1998 with CXT revision K6-2.
Which is what really caught the clone cpu makers out, FPU's up to that point were essentially only for the small professional market. Quake made it a requirement and highly valued a pipelined one. Cyrix probably would have been a much bigger success if Quake had never existed. Cyrix's FPU is quite good, it just wasn't pipelined like the pentiums.
There was also Cyrix EMC87 with memory mapping. But without special support it performed the same as regular Cyrix FPU. I have it but don't know of any program that supports it
Again, before it was clear that a FPU integrated onto the CPU was the future, memory mapped FPU's could have been. The 286 and 386 were only really limited by the FPU access mechanisims, the XT didn't care, and 486's and beyond it was tightly integrated you didn't dump lots of cycles accessing it. Writing code for different types of FPU access was a PIA.
In theory you could have made a 50Mhz or 60Mhz bus 386 socketed motherboard, and put a CPU and FPU on that (if intel had locked out sockets like they did on pentium II and greater). But it still would suck, and clock doubling would get you very little, and VLB working at those freq would have been impossible. If you think about Macintoshs, the IIFX was really a jumped up 386 (68030) equiv. They did do 40mhz bus, 50Mhz+ accelerators (motorola has 50mhz cpus and FPUS). For $9000 usd at the time.