Periodically, the operating system embedded in a game will intentionally deny access to the floating point coprocessor CP1. The OS achieves this by setting a bit in Coprocessor 0's STATUS register. Then, when a floating point instruction attempts execution, flow control is switched to the exception handler routine to service the exception. After that, flow should return to the floating point instruction that initially caused the exception, or the instruction that immediately precedes it, depending on where it is in the code. You may notice a minor speedup with this off, but in some games this may result in odd effects - usually weird video problems. We strongly recommend that you leave this on for maximum compatibility.
- Turning this off can get a tiny bit more speed out of the thing, but it is recommended that you leave this on. Interestingly, some a few games require it off (Tom&Jerry). The FPU Hack option is an additional check in the FPU to test for what is known as a Coprocessor Unusable Exception. Refer to MIPS documentation for information about it if you are interested.