Need explanation of the CPU and FPU technology on turbo boards

[alexh]

kidkoala wrote:
1. what is the connection between the fpu and the crystal?

For 68882 FPU's the crystal speed is 1:1 to the FPU speed. Use a 40MHz Crystal, FPU runs at 40MHz etc.

can i just put in the fastest fpu and crystal there is? (says something about max. 33mhz in my primitive papers on the sx32).

It depends on the accelerator, but in general YES.

2. can i put in the fastest cpu i find? (like a 50mhz or something), is there a connection between the cpu and the fpu speed?

The 680x0 and FPU can run asynchronously, but I believe that the CPU has to feed the FPU both instructions and data and so if there is a BIG gap between speeds (14MHz 020 & 50MHz 68882) then the FPU will spend a lot of it's time waiting. There is pipelining in the FPU so it's not a 1:1 relationship.

4. what is the fpu used for (i know about floating-point operations, but what is that, and give me some examples of which programs/games use it and which doesn't)?

The answer is mainly nothing. Very few games will use it. A few CAD like things (SCALA, Lightwave etc.) will use it.

[alexh]

Hyperspeed wrote:
Hang on, I thought quite a few games used it?

Not to my knowledge. A handfull if that. Usually ports like Quake etc.

Does software specifically have to call on an FPU or will the FPU just cooperate to un-burden the CPU's task of dealing with floating point maths?

The code has to have been written to use an FPU or a maths library.

With the '040/060 the FPU is internal so it might be different with the '020/'030 CPUs...

Games dont use the '040/060 FPU any more than a 68881/2

I wonder if Shapeshifter/Fusion and other emulators use it.

I think that they do. But the question is "Does any MAC software of that day use the FPU?" I think it is just as unlikely.

[alexh]

rkauer wrote:
Just a memo: you could NOT use a faster FPU than your CPU. If you bought a faster FPU, simply put a cristal the same clock of CPU.

That is just not true. They run asynchronosly in most designs. If it has a separate crystal socket it was designed to run at a different speed to the CPU!

Hyperspeed wrote:
What would be the difference between a CPU's FPU and a modern day GPU? Both seem to be gauged in FLOPS?

Too many to mention. GPU's are not usually measured in FLOPS (FLoating point Operations Per Second) but in pixels/texels per clock, or more commonly now in the number of pipelines and shaders.