This repository preserves and maintains the DOS/32 Advanced DOS Extender source. The active tree is the DOS/32A 26.1 maintenance branch under src/, with older 7.35 and 8.00 trees kept as historical references.

DOS/32A is a 32-bit DOS extender and a drop-in replacement for DOS/4GW and compatible extenders. The maintenance goal is to combine useful fixes and behavior from the 7.35, 8.00, and 9.1.2 releases: HDPMI32 compatibility for linear frame buffer write-combining, the 8.00 speed-loop changes, and the 9.x SSE support. Version 26.0 was the first stable release from this maintained line; version 26.1 carries low-risk compatibility fixes on top of it.

• src/dos32a/ - active DOS/32A extender assembly sources.
• src/dos32a/text/ - included kernel/client assembly text.
• src/stub32a/ - active STUB/32A and STUB/32C assembly sources.
• src/sb/ - SUNSYS Bind Utility sources.
• src/sc/ - SUNSYS Compress Utility sources.
• src/ss/ - SUNSYS Setup Utility sources.
• src/sver/ - SUNSYS Version Utility sources.
• dos32a-735-src/ - historical 7.35 source tree.
• dos32a_800/ - historical 8.00 reference distribution, including binaries, documentation, examples, and sources.

Useful references include ChangeLog, archived readmes in the source trees, and the HTML documentation under dos32a_800/docs/.

The active 26.1 sources are built with the historical DOS toolchain family. This checkout provides Windows batch wrappers so the tools do not need to be added to the machine-wide PATH.

Required local tools:

• Open Watcom installed at C:\WATCOM. If it is installed somewhere else, set WATCOM before running the build.
• TASM 5.3 setup/patch files under tasm5\ in this checkout. The build uses tasm5\PATCHES\53_WIN\TASM32.EXE.
• DOSBox-X installed at C:\DOSBox-X\dosbox-x.exe for runtime smoke tests. If it is installed somewhere else, set DOSBOX_X before running the smoke test. Use a DOSBox-X build with integrated DOS; the OS-Free build requires a separate bootable DOS image and will not run the provided smoke test directly.

From a Windows Command Prompt or PowerShell in the repository root, verify the expected tool paths:

dir C:\WATCOM\BINNT\wcl.exe
dir tasm5\PATCHES\53_WIN\TASM32.EXE
dir C:\DOSBox-X\dosbox-x.exe

To configure an interactive Command Prompt for ad-hoc tool use, run:

build-env.cmd

When calling it from another batch file, use call build-env.cmd so control returns to the caller. PowerShell users can run build.cmd and smoke-dosbox.cmd directly; environment changes made by build-env.cmd do not persist back into a parent PowerShell session.

Build all active 26.1 components:

build.cmd

The build writes generated binaries to binw\ and removes source-directory intermediates. Individual components can be built with:

build.cmd dos32a
build.cmd stub32a
build.cmd sb
build.cmd sc
build.cmd ss
build.cmd sver

Remove generated outputs and intermediates with:

build.cmd clean

The build wrapper uses the archived 8.00 h32\ and src\sutils\misc\ include files already in this checkout. The original 9.1.2 readme states that building requires the v7.1 SDK, and the historical 8.00 source documentation records Borland Turbo Assembler 5.x and Watcom C/C++ as the toolchain family used for that line.

The checked-in tasm5\ directory contains third-party historical assembler tool media and patch files used only to reproduce this build environment. Those files are not part of DOS/32A and are not covered by the DOS/32A license.

Do not assume a modern host compiler can reproduce the historical binaries. Any build notes should identify the exact SDK, TASM and Watcom versions, host environment, DOS or DPMI runtime, and source tree used.

After build.cmd, run:

smoke-dosbox.cmd

The smoke test stages temporary files under C:\DOSBox-X\drivez and runs:

SVER.EXE DOS32A.EXE
DOS32A.EXE HELLO.EXE
AHELLO.EXE

A successful run reports the generated DOS/32A version, for example:

DOS/32 Advanced DOS Extender:
Version:        26.1

There are no automated tests in this checkout, so validation must be explicit and reproducible.

For utility changes, document the exact command path exercised and the files used as input and output. For extender or stub changes, record the affected binary path, the DOS/DPMI runtime, host environment, and observed runtime behavior. Low-level extender, binding, compression, and generated binary changes should be treated as compatibility-sensitive.

The active source is distributed under the DOS/32 Advanced DOS Extender Software License. See LICENSE for the complete terms.