Update
This port is now outdated. The latest ports of 86-DOS to the IBM PC are on GitHub and binaries may be downloaded from there too.
This is not a writeup, the port is still WIP. I’m just dumping whatever I’ve done here for people to see, because xmas and new year holidays are now over and I don’t want to devote any more of my very limited free time to projects like this.
A few days ago, Gene Buckle uploaded 86-DOS 0.11 and 0.34 to the Internet Archive. After about 2 hours of coding and debugging, perhaps the oldest surviving piece of x86 software booted on the (emulated) IBM PC:
I didn’t do anything too fancy – just modified the BIOS from my 86-DOS 1.14 port to simulate 128-byte sectors. As with my 1.14 port, I patched the kernel to use PC-DOS’ special editing commands, patched RDCPM to read CP/M-86 disks and rewrote SYS.
Everything works, but it is slow as a sloth. To workaround the stack overflows, I made the BIOS switch to an internal stack for every single call. Also, I did not implement buffered I/O – sequential reads are 4 times slower and sequential writes are 8 times slower (though I do have experimental buffered disk reading code).
If you’re interested in improving my code or implementing proper buffered I/O, drop a comment here and I can send you my BIOS source code.
Random note: 86-DOS 0.11’s FCB search function returns a 16-byte directory entry, rather than an unopened FCB. This makes its COMMAND.COM misbehave under later DOS versions.
Last thing – I have a plan to reconstruct the source code of 86-DOS 0.11, because this version is historically significant, it’s the earliest version of DOS (apart from QDOS 0.10, which was never released). I have already disassembled some binaries, but they’re really just the low hanging fruits like COMMAND.COM, SYS.COM and HEX2BIN.COM. If you have experience reverse engineering 8086/DOS code, please consider helping out, thanks!!
Edit: It’s been a week, I’ve contacted a few people and nobody is willing to lend a hand. I’m just going to reup the binaries with IO.ASM and SYS.ASM. If you’d like to contribute, go ahead and use these sources!
WIP PC port + COMMAND.COM, SYS.COM and HEX2BIN.COM src: https://mega.nz/file/4EZ2kLCB#pNJ4iRM2DqsQ9YJ9oAZWTsn4DLy0dH3LpsRdJDCel6U
Edit 2: With IO.ASM and SYS.ASM:https://mega.nz/file/JZpUBRKL#0ANcb2NKVELClamu0kRZknhl4WrHhXn7r_df9NabPXY
Edit 3: PC port and source code reconstruction are now on GitHub.