> No. The BIOS needs to perform some touchy, hardware-specific initialization -- like detecting and calibrating RAM -- before releasing control to user code. It's not something you'd want the OS to be responsible for.
I don't feel like the person you're responding to suggested that the OS should be responsible for it; he/she just wondered if it is possible to have the CPU not have to jump through 16-bit real mode and 32-bit protected mode just to get to 64-bit.
I see no fundamental reason why it should be impossible for the BIOS to do its initialization work in 64-bit mode. There's the issue of paging and the page-table perhaps, but it seems trivial enough to suggest that the CPU could initialize with a very basic 1:1 mapping between virtual memory and RAM.
That said, I don't know if such a thing would ever actually happen, since I imagine that it would suggest re-writing a lot of code.
I don't feel like the person you're responding to suggested that the OS should be responsible for it; he/she just wondered if it is possible to have the CPU not have to jump through 16-bit real mode and 32-bit protected mode just to get to 64-bit.
I see no fundamental reason why it should be impossible for the BIOS to do its initialization work in 64-bit mode. There's the issue of paging and the page-table perhaps, but it seems trivial enough to suggest that the CPU could initialize with a very basic 1:1 mapping between virtual memory and RAM.
That said, I don't know if such a thing would ever actually happen, since I imagine that it would suggest re-writing a lot of code.