[torh]

I wonder how much time is spent on getting the processor from 16-bit Real Mode and up to the full 64-bit mode.

[amluto]

A few tens of microseconds, most likely.

[AnIdiotOnTheNet]

It is interesting how even people in this industry are sometimes orders of magnitude off when thinking about how quickly a modern computer is able to do something. Personally, I think it is because web development has trained people to believe that computers are slow.

[d_tr]

Just switching is a few tens of instructions. Tens of microseconds should be more than enough to also build a non-trivial page table.