AFAIK the entire idea dates back to the days of the 80286/80287 (and 80386/80387) when accessing the coprocessor was slow, and a TSS switch (Linux used it until

AFAIK the entire idea dates back to the days of the 80286/80287 (and 80386/80387) when accessing the coprocessor was slow, and a TSS switch (Linux used it until the late 1990s) set that bit for you.