Originally , it supported up to 64 kb of main memory . It was command-line based , and came before MS-DOS . Since MS-DOS had access to more memory ( as few IBM PCs were sold with less than 64 KB of memory , while CP\/M had to run in 16 KB if necessary ) , more commands were built in to the command-line user interface logic , making MS-DOS somewhat faster and easier to use on floppy-based computers .