Advanced Micro Devices Inc (AMD)

[HailMary]

Is the segmentation such a big deal? Isn't it just adding some registers together to get an effective address?

Address calculation in a segmented world adds to the time it takes to get a lookup address, so it is likely multiple hardware paths have to be implemented to allow both flat and segmentation modes to work optimally. This adds to the complexity of the implementation.

You point out some good cruft that is limiting.

x86 will never lose some of those things like variable length instructions, to which a couple of pipe stages are dedicated to scanning and aligning instructions for decode. I guess the benefit of more efficient use of cache/memory for instructions works in its favor. Intel gets around this a bit by having the trace cache, but that just points out even clearer the x86 baggage.

Some of the other stuff can be phased out. Many old instructions are done in microcode, so there is little affect on the hardware, although these would still have to be verified as functional, so it adds to the design cycle time. I'm willing to bet many of the old instructions have been declared as don't use by new compilers or even current compilers. Of course there may be tons of existing 32 bit apps that use these. The true phase out comes when there are no longer any 32 bit x86 apps, but that is 10+ years away, if we are lucky.