Older versions of DOS running on a Jr?

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Older versions of DOS running on a Jr?

Postby OldComputerGuy » Tue Jan 21, 2020 8:29 am

Has anyone managed to get any version of DOS starting with a 1 to run on a Jr? I may have a source for a physical copy of PCDOS 1.1 is why I ask.
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Re: Older versions of DOS running on a Jr?

Postby KenG » Tue Jan 21, 2020 6:23 pm

I believe DOS 2.1 was the first version to support the PCJR. I imagine you would have to patch the boot sector on an older DOS the same way you have to for DOS 5 and beyond to get it to work. There may be other considerations that I am not aware of.
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Re: Older versions of DOS running on a Jr?

Postby Brutman » Tue Jan 21, 2020 6:59 pm

The patch for DOS 5 and up is required because DOS 5 and up require 256KB machines, and a stock PCjr will only report 112KB.

Don't bother booting DOS 2.0 or earlier on the machine. I tried it and the machine crashes if you look at it incorrectly. They were quite buggy and they don't have the correct stepping parameters for the floppy drive, so it sounds like hell when the floppy drive is seeking. And functionally there is no reason to run those older versions.
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