MS-DOS 1.25 is the first version of MS-DOS, released in 1982-08. It was the first version licensed to OEMs beyond IBM or Seattle Computer Products. Some OEMs labeled their release with different version numbers (e.g. COMPAQ), but it seems they're still all based on 1.25.
It only supported 5.25" 160 kB floppies and did not support folders (all files had to be located in the root directory). The command interperter,
COMMAND.COM, supported these commands: