I didn't know it was common for operating systems to let user-mode code adjust the memory segments and for them to persist those changes between context switche

I didn't know it was common for operating systems to let user-mode code adjust the memory segments and for them to persist those changes between context switches. It seems like a pretty niche feature to have in a 64-bit operating system, though I'm glad it's there. I only recently tried to run a 16-bit program in Wine on a 64-bit machine and I was pleasantly surprised to see it work perfectly.