Not exactly, especially in the context of this issue. You could use the MMX registers as 'traditional' registers (or at least a scratchpad), not quite like the

Not exactly, especially in the context of this issue. You could use the MMX registers as 'traditional' registers (or at least a scratchpad), not quite like the x87 stack. There are 8 64-bit MMX registers. To avoid having to add new registers, they were made to overlap with the FPU stack register. This means that the MMX instructions and the FPU instructions cannot be used simultaneously. MMX registers are addressed directly, and do not need to be accessed by pushing and popping in the same way as the FPU registers. [1] [1] https://en.wikibooks.org/wiki/X86_Assembly/MMX https://en.wikibooks.org/wiki/X86_Assembly/MMX