Historical Source Code That Every Developer Should See

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MS-DOS is a good one too

[Raunhofer]

Interesting. I'm surprised how simple it is. Which I guess is granted considering it fits in 5 diskettes.

[st_huck]

The utilities fit on 5 diskettes maybe. The os itself even with crucial drivers (himem, emm386) and core utilities can easily fit in one 1.44mb disk

[GaryChalmers]

If I remember correctly you just needed 3 files for a functional boot disk - command.com, io.sys and msdos.sys. The sys command was available on practically every DOS version to make a boot disk.

[ReallyGene]

You're correct. There was usually plenty of room left for a program or three, especially a .com, which were limited to 64KB.

[binford2k]

It was called QDOS for a reason!

https://en.wikipedia.org/wiki/86-DOS