Also, even if you only had one physical floppy drive, it would still respond to A: and B:, albeit as split personalities. What I mean is that you could stick your programs disk in there and type A:EDITOR.EXE to run some editing program, and then go to save your document and type B:MYDOC.TXT as the filename, and DOS would know that you wanted to write this file to a different floppy, so it would day, "Insert disk for drive B and press enter", prompting you to swap the floppies. Then, when the editor program needed to access some of its files again, it would try to access, say, A:LIBRARY.OVL, and DOS would know that meant it was time to prompt the user to swap disks again.
At that time (okay, a little later, but there was some overlap), I was using RISC OS. Its disk format allowed for each disk to have a name, which would be used in fully qualified filenames (e.g. ADFS::MyData.$.Docs.Resume). The OS could then ask for the disk by name (MyData).
