Comment by JoeAltmaier

Oh I remember SYSENTER/SYSEXIT, I think. I worked on CTOS, widely released by Burroughs/Unisys back then. CTOS used all the clever instructions. They performed badly. Later I learned from an Intel customer consultant on porting code, that we were the only ones who ever embraced fancy things like task gates etc. Everybody else just continued using regular push/pop and simple traps. Because they ran faster.