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MSDOS 4 was reportedly an overall bad release and was not in wide circulation, in all my days I think I only came across it once. This is why DOS 3.3 and 5.0 were much more common to find in circulation together.

I'm sure the source for 4 will make for some interesting bug hunting. Anyone remember the MUF list? "Microsofts Undocumented Features".

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This is "multitasking dos 4" though, which isn't the same as the much-reviled ms-dos 4. As I understand it, it's a lot closer to dos 3 than it is to dos 4 in terms of functionality.

I wouldn't expect this to understand extended partitions, much less large partitions (that dos 4 uses)

>I wouldn't expect this to understand extended partitions, much less large partitions (that dos 4 uses)

Most of the source code (everything outside of -ozzie) is for regular DOS 4.0 and supports 32-bit sector numbers. They planned to add it in the multitasking version as well [1], but from reading IBMDSK.ASM it isn't there yet.

Also that driver talks directly to the hard disk controller instead of going through the ROM BIOS, and will only support XT drives, not IDE/ATA. Apparently the goal was to be able to do background I/O on an XT, where there is no BIOS support for that.

[1] see driver docs at https://raw.githubusercontent.com/microsoft/MS-DOS/main/v4.0...

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