open-watcom-v2 VS MS-DOS

https://github.com/open-watcom/open-watcom-v2

In terms of ISO-complianceness, perhaps don't expect much. It basically C89 (the C99 support is still incomplete), and for C++... most likely not even C++98 - compliant.

> You will also want to start with a 16-bit C compiler like Borland Turbo C or Microsoft C

The parent post mentioned they're going to use OpenWatcom which is an actively developed[0] C and C++ compiler that targets 16bit DOS (among others).

[0] https://github.com/open-watcom/open-watcom-v2

Despite the lack of feature support, the compiler is still updated to this day, and still does support DOS, Windows, Linux, and OS/2, so it's modern in the sense of maintenance, just not really standards support. If you got further questions, I can send you the Discord link. They are pretty friendly.

My advice is, when you feel you need that challenge, install DOSBox or DOSBox-X and Open Watcom C/C++, DJGPP, or gcc-ia16 and do some retro-programming. You'll also get the fun of being able to do low-level hardware twiddling and rely on DOS being so simple that it's effectively an RTOS.

If you want to build under Linux, I would recommend you look at Open Watcom. It's the best open source 16-bit x86 C compiler, IMHO.

I have recently found out that Watcom C still exists. And not just exists, but there are plenty of commits.

I should note, that OpenWatcom 2.0[1] is far better for supporting more recent C and C++ code, modern hosts and tooling, but still able to compile into 16 bit code. It is also actively maintained. Instead of MASM I recommend JWasm[2] + Jwlink[3]. Back in time I did a fork[4] of JWasm that has cleaner build system (CMake).

[1] https://github.com/open-watcom/open-watcom-v2

[2] https://github.com/Baron-von-Riedesel/JWasm

[3] https://github.com/JWasm/JWlink

[4] https://github.com/JWasm/JWasm

If you want to run this in DOS: the code under src/should actually compile with this OpenWatcom fork via the -za99 flag. MiniFB however will not compile. You'd have to palettize the output pixel buffer to 256 colors and then blit it to 0xa000if you fancy that.

GCC, clang or maybe watcom? You wouldn't find it there (before invention of AGI, but that would be entirely different can of worms).

This 4.0 code contains references to 4.00, though: https://github.com/microsoft/MS-DOS/blob/main/v4.0/src/BOOT/...

I recently stumbled across the MS-DOS 1.25 and 2.0 source code [1].

[1] https://github.com/microsoft/MS-DOS

“Despite this reduction in scope for MS-DOS 2.0, it did carry many bits of XENIX. The system adopted I/O redirection via less-than and greater-than symbols, piping, a hierarchical directory tree, file handles […]”

The source code for MSDOS 2 is available and the file descriptor stuff appears to be in https://github.com/microsoft/MS-DOS/blob/master/v2.0/source/... and XENIX2.ASM. It stands in contrast to the File Control Block API which MSDOS 1 (née 86-DOS) modeled after CP/M’s API.

Asynchronous I/O figures in prominently in Windows NT. I was really surprised to see[0]:

Each driver in the chain defines two entry points; the strategy routine and the interrupt routine. The 2.0 DOS does not really make use of two entry points (it simply calls strategy, then immediately calls interrupt). This dual entry point scheme is designed to facilitate future multi-tasking versions of MS-DOS. In multi-tasking environments I/O must be asynchronous, to accomplish this the strategy routine will be called to queue (internally) a request and return quickly. It is then the responsibility of the interrupt routine to perform the actual I/O at interrupt time by picking requests off the internal queue (set up by the strategy routine), and process them. When a request is complete, it is flagged as "done" by the interrupt routine. The DOS periodically scans the list of requests looking for ones flagged as done, and "wakes up" the process waiting for the completion of the request.

I didn't realize that kind of forwarding-looking perspective was going into the design of MS-DOS.

[0] https://github.com/microsoft/MS-DOS/blob/master/v2.0/source/...

>Any others I'm missing?

I would suggest MS-DOS: https://github.com/microsoft/MS-DOS