DOS 4

Looks like they just released the source code for DOS 4. Seems like an odd thing to boast about because, as I recall, DOS 4 was a horrible failure. I experienced this first hand, because I bought a computer that came with an OEM version of DOS 4.

DOS 4 had so many problems that most existing users didn't upgrade, but just continued using DOS 3. Only poor saps like me ended up with DOS 4. It wasn't until DOS 5 came out that people upgraded.

I remember seeing a presentation on DOS 5 from Microsoft folks at work. They basically apologized for how awful DOS 4 was and promised that DOS 5 wasn't like that. It was pretty great. They played a version of Take Five in 4/4 time, which of course, sounded terrible. It was clumsy and irritating, just like DOS 4! Then they played it again in 5/4 and it sounded lovely as usual.

The presentation worked on me; I bought the DOS 5 upgrade when it came out.

Coincidentally, the same thing happened with NT some years later. We had NT 4 at work, but it was such a hot mess that most other customers continued using NT 3. It wasn't until NT 5 (which was renamed "Windows 2000") was released that NT 3 really started going away.