That was the first 'DOS' with support for those whopping big drive **, later to be known as a hard drive .... Folders or subdirectories also dates from that moment.
The DOS that makes the computer boot without a floppy. That was yaw dropping technology.

edit : ** something close to 20 mega bytes, but there were always bad sector right from the beginning. remember : the 3.5 inch 1,44 Mbytes floppies didn't exist back then. 5.25 floppies were single sided (?) - or something like 180 Kbytes.
I do recall also :

debug

and then

g c800:0

to do an initial low level C drive format.

and I just found out that we don't have 'debug' any more .... ;)