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I looked at it pretty close and eventually the code was published in the IBM PC Tech Ref manual and it looked to be the part that IBM contributed.

So why would they need to "reverse engineer" it in the show?

Copyright issues. A direct copy would have been illegal and IBM would have crushed them. If I recall correctly the clones did exactly what is described in the program; put programmers in a locked room and described a task and had them come up with a solution independent of the actual IBM solution.

And it's been a while but I seem to recall one of the more difficult parts was the section of the BIOS that read "COPYRIGHT IBM". I'm pretty sure the IBM version of DOS read the BIOS and looked for that string and if it wasn't there it wouldn't load.

But since IBM didn't have an exclusive on DOS from Microsoft it was possible for the clone makers to come out with their own versions with subtle differences thus you had Compaq DOS, etc. After a bit MS produced generic versions branded by them.

In 1987 I was in a waiting for an interview. I picked up a technical news paper. One small article caught my eye. It basically said that, as soon as the South Koreans managed to reverse-engineer American desktop computers/components/software, the US prices would drop.

At the time, a complete desktop set up — computer, monitor, printer & peripherals — could easily cost over $6,000.

About 2 years later, the SK’s were importing desktop pcs and components. Prices dropped significantly. An entire system (computer, printer, monitor, peripherals) were around $3,000.