Unless you need to load anything else other than what's in that sector, because ...

p_l 11 months ago | parent | context | favorite | on: Writing a BIOS bootloader for 64-bit mode from scr...

Unless you need to load anything else other than what's in that sector, because you can't fit enough I/O drivers into one sector to load the rest of the OS.

Unless you're targeting S/360, but even there XA and newer made it a bit more complex.