I seem to remember my old Commodore 64 being fully booted and READY at its BASIC REPL in about a second. Shorter than it took for the CRT to warm up. A computer from 40 years ago. How we have fallen!
Both atari 8 bit and commodore had a disk drive with a trimmed down 6502 in it so you basically bought a second computer. This is why the drives cost more than the computer itself.
So the atari was relatively fast! I never knew. I didn't have the disk drive until I was much older.