[userbinator]

An OS doesn't need to have networking, permissions, or anything else. It just needs to provide a common set of services for applications programs to use.

Consider that OSs started out as libraries of functions that programs could call into, which then evolved into job managers, that is where MS-DOS fits.

It's single-tasking, single-address-space, but it already has the concept of processes, drivers, files. This is still more than some embedded OSs which are not much more than a threading library.

[wtallis]

Really though, wasn't most of DOS just thin abstractions on BIOS interfaces? What hardware abstractions did it provide other than the filesystem, and what services other than an ABI allowing you to quit a program without rebooting?

[userbinator]

http://en.wikipedia.org/wiki/MS-DOS_API

Given that it was a disk operating system it's no surprise that the bulk of the services are disk/filesystem-related, but it also has ones for I/O, memory, timing, and processes.

[caf]

It abstracted the character-at-a-time BIOS interfaces to a line-buffered text console.

It provided a memory allocator service.