http://en.wikipedia.org/wiki/Apple_DOS
My 33 figure was wrong (either me or Wikipedia). Maybe the directory entry had 33 bytes (30 for the file name, 1 for type, and two for track and sector)
fd0: was floppy 1. If you had an additional drive, that would be fd1: etc. The best part was that you could also access devices by file-system label, so if you needed to make sure you were accessing not only a floppy, but the device labelled "WorkbenchExtras" you would simply do WorkbenchExtras:
Needless to say, this made multi-disk tasks & scripting rather pleasant, easy and cut out lots of boilerplate and checking.
It was a nice system and I kinda miss it.
Edit: df0: was floppy 1. dh0: was first harddrive, etc. Not that in changes much.
SUBST on Windows is similar, but with 1/10th of the power and just single drive letters.
I miss the Amiga too, but it simply never kept up the pace.
I just thought it might be slightly out of scope for the discussion at large, so I decided not to include it ;)
Just to imagine most today's PCs deal with cruft that dates back to the CP/M days is... disgusting.
Apple's ProDOS also had something like that - the volumes were named and you accessed files with /VOLUMENAME/FILE.DAT paths.