How could a disk drive ever be faster than RAM or ROM, Eddie? Have you ever loaded a BASIC from disk quicker than the *BASIC command (from ROM)? No way, Mate. The now familiar PC "booting-up" (from disk) is all about selling software, and nothing to do with speed or efficiency.
Why not have a go at burning XP into ROM (but what would you run it on)?
The BBC Micro was a clever design, and one that should have been taken further (that is, beyond the Master and up to more recent times). I believe that the grand BBC Micro project fizzled out when (for some perverse reason) the BBC started getting rid of its engineering and R&D facilities (and genius guys like RTR) so it could start paying moronic newsreaders and foul-mouthed "presenters" million £££ salaries. In a way, it just about sums up the state of play in Modern Britain!