A few things: x86-64 uses a 4-level page-table, which is much more annoying to get right then a 2-level page-table if you're not familiar with paging or haven'

A few things: x86-64 uses a 4-level page-table, which is much more annoying to get right then a 2-level page-table if you're not familiar with paging or haven't dealt with it before. I agree about TSS - nobody really bothers using it anyway. That said, x86-64 has a bit more state to handle when doing a context-switch (Though nothing very extreme) x86-64's calling convention is more complex then x86's calling convention. For this project it doesn't really apply because it isn't followed anyway, but for a C project it would come into play. IMO, another big issue with doing x86-64 is documentation - x86 has tons, x86-64 has comparatively little. I would definitely agree that if you know what you're doing the differences aren't huge, but if you don't know what you're doing I think you'll definitely have an easier time getting stuff working with x86.