MSDOS.SYS 2.00 build directory                   John Elliott, 20 October 2018
==============================================================================

This is an attempt to adapt the MIT-licenced incomplete MSDOS 2.11 source 
release at <https://github.com/Microsoft/MS-DOS/> to build, byte-for-byte,
the 2.00 MSDOS.SYS also present in that release.

Since MSDOS.SYS was in the MIT-licensed release, I reasoned that it was 
permissible to disassemble it and use it to recreate the missing source.

Build requirements:
* MASM 4.00 (MASM 3.00 may also work)
* LINK (I used LINK.EXE from Visual C++ 1.52; Microsoft LINK 2.40 also works).
* EXE2BIN (I used EXE2BIN 1.00 from DRDOS 6)

Build scripts:
* MK.BAT    builds MSDOS.SYS
* CLEAN.BAT removes intermediate build files
* ZIPIT.BAT builds the zip file containing everything

Changes I have made to convert the 2.11 source to 2.00 are mostly flagged 
[JCE], for ease of examination. My main contributions (based on disassembly)
are the files STDIO.ASM, IO.ASM and IO2.ASM.

Things I have not tried, but might be worth experimentation:
> Building with IBM defined, to produce a PC-compatible MSDOS.SYS rather 
 than the generic one supplied.
> Using the source tree to build MS-DOS 2.11 rather than 2.00.
> Building other bits of MS-DOS.
> Fixing that bug in DEBUG where it creates PSPs with the CALL 5 address 
 two bytes too low.
