> I thought it was by and large dropped in 64-bit mode? Indeed: cs, ds, ss and es cannot be used in 64 bit mode (source: https://en.wikipedia.org/w/index.php?t

> I thought it was by and large dropped in 64-bit mode? Indeed: cs, ds, ss and es cannot be used in 64 bit mode (source: https://en.wikipedia.org/w/index.php?title=X86_memory_segmentation&oldid=728102976#Later_developments https://en.wikipedia.org/w/index.php?title=X86_memory_segmen...), but fs and gs can still be used. On x86 in 32 bit they are never used at least in ring 3. So not much difference. fs and gs may still be used in both x86-32 and -64 and gs is for both: Under Windows for accessing the Thread Environment Block and under Linux for accessing per-CPU data.