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posted by janrinok on Saturday January 08, @08:10PM   Printer-friendly
from the PC-introns dept.

Anyone trying to disassemble the PC DOS 1.1 boot sector soon notices that at offsets 1A3h through 1BEh there is a byte sequence that just does not belong. It appears to be a fragment of code, but it has no purpose in the boot sector and is never executed. So why is the sequence of junk bytes there, and where did it come from?

The immediate answer is "it came from FORMAT.COM". The junk is copied verbatim from FORMAT.COM to the boot sector. But those junk bytes are not part of FORMAT.COM, either. So the question merely shifts to "why are the junk bytes in FORMAT.COM, and where did they come from?"

It is not known if anyone answered the question in the past, but the answer has been found now, almost 40 years later—twice independently.

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  • (Score: 3, Interesting) by looorg on Sunday January 09, @08:04AM

    by looorg (578) on Sunday January 09, @08:04AM (#1211216)

    While this does sound like a plausible explanation I sort of wonder why you would allow this junk into the program tho if the goal was to save bytes of memory? You probably would also waste bytes of storage, which at the time also was quite expensive. Wouldn't it have been a lot better in that regard to just zero it out, or just make it something controlled so it could be compressed better?

    In that regard I almost wonder if some of it was left in there as a copyright claim. Considering there was a multitude of DOS:es etc at the time things was probably left behind there for all the people that copied your stuff so you could later claim they copied you and it was lawsuit time. So instead of leaving something legible you leave some "junk". Sounds like something Bill and friends would do.

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