So, if a mac DID use letters, what would its C drive be? That's my question...Does it make sense?
Maybe it would help if you explained what you are trying to figure out, or do?
Windows, while no longer DOS based is still using many of the terms from way back when these things were hardcoded into the OS. OS X, coming from a different lineage that never used Drive Letters (Like C:, or A: for floppies) doesn't really have an exact equivalent.
I don't know if it's still true for Windows, but once upon a time you designated a certain drive or partition as the C: drive, and then that was the drive that the OS tried to boot from. And if there wasn't an OS there, you didn't boot. So - you set the C: Drive, and
then you put the system files there.
There were limitations too on where the C: could go. Ah yes, the good old days. Whether or not those limitations still exist in Windows, that terminology still exists in working with the OS.
OS X boots from whichever drive/partition has system files, and iirc, is formatted to be bootable. There are no drive letters for the drives/partitions - just names. So you put the system files where ever you want, then boot from there.
This is all based on a non-professionals understanding of how things worked, though over the years I've messed around with my fair share of partitions etc.
Does that help?