Segment registers are precisely how NT does context switching. I think it may be restricted to just switching from user- to kernel- threads. I can't remember if

Segment registers are precisely how NT does context switching. I think it may be restricted to just switching from user- to kernel- threads. I can't remember if there's thread-to-thread switching using segment registers — I feel like this was a thing, or it was just a thing we did when we tried to boot NT on Larrabee. (Blech.)