What operating system support is required for the Pentium III?
Both MMX and 3DNow! were aliased onto the floating-point registers so that no additional processor state had to be introduced. This meant all existing operating systems could continue to work without modification. However, the eight new extended multimedia registers found in the Pentium III add state to the processor, and the operating system must be aware of this when switching tasks. To help, Intel added two new instructions, FXSAVE and FXRSTOR, which save and restore a whopping 512 bytes of state. Within these 512 bytes are the SIMD registers, the floating point/MMX registers and various control registers. These new instructions actually first appeared in the late-model Pentium II processors, and their presence is indicated by the CPUID instruction and by checking the FXSR bit in the features.
