The Commodore 64 Kernal is in a ROM so it is a fast boot for the OS, but the 1541 floppy drive is slow unless you use Fastload or Jiffydos, etc.
I think some C64 units had a spare socket for GEOS the GUI made for the C64.
I think some C64 units had a spare socket for GEOS the GUI made for the C64.