before disks, there wasn't as much need for the concepts of an "operating system" in microcomputers. "what is a file?" and so on are more complicated with disks

before disks, there wasn't as much need for the concepts of an "operating system" in microcomputers. "what is a file?" and so on are more complicated with disks than with tapes, and its much more useful to have those conventions stretch further than the single make and model byte stream formats used for tapes. writing block number ranges on disk labels to keep track of where files are is no way to go about computing.