I dont know for sure but I think non +drive is limited to one bank of userwaves.
The drive gives you 128 banks of waves which is very handy. Depends how you work, but if you think of one bank as say 64 organ waves or 64 strings, squares, pianos, 8-bit, etc etc then that gives you 64 waves to audition through a digi pro machine until you find the right sound within that ‘genre’. And the banks are hot-swappable.
Without the drive you have 1 bank of 64 waves that either holds just say “strings”, or you could have different types of waves at different positions in the bank:
- Fat String
- Cheese String
- String Vest
- Square
- Squarish
- Moogermeister
- Wasp
.
.
.
- DX Piano
So the drive is way more convenient as you can flick through several wave banks without having to sysex up into one bank whenever you need a change.