A working fork of MS-DOS 4.0 that builds from source on Linux and macOS, boots in QEMU, and has full E2E test coverage — intended as a stable base for OS-level experiments.

The build uses the original DOS compilers (MASM, CL, LINK) running under kvikdos (a headless DOS emulator — KVM on Linux, software 8086 CPU on macOS).

• /? help for every tool — all 38 CMD utilities and all COMMAND.COM built-in commands have /? usage text (none existed in the original source)
• Bug fixes — FOR/SET/PROMPT hang (ES register corruption), COMMAND.COM parser crash (signed comparison overflow), FDISK R6001 and semicolon bugs, EDLIN binary mode fixes
• Full E2E test suite — kvikdos fast tests for all built-ins and most tools; QEMU+serial tests for disk ops, TSRs, interactive prompts, FORMAT geometry, FDISK partitioning, driver loading
• CI — GitHub Actions on every push; parallel QEMU jobs cover all test targets

IO.SYS, MSDOS.SYS, EMM386.SYS, MAPPER.LIB, boot.inc, shared kernel objects, SELECT.{EXE,COM,HLP,DAT}, USA-MS.IDX

COMMAND.COM, FORMAT.COM, SYS.COM, CHKDSK.COM, DEBUG.COM, MEM.EXE, FDISK.EXE, MORE.COM, SORT.EXE, LABEL.COM, FIND.EXE, TREE.COM, COMP.COM, ATTRIB.EXE, EDLIN.COM, FC.EXE, NLSFUNC.EXE, ASSIGN.COM, XCOPY.EXE, DISKCOMP.COM, DISKCOPY.COM, APPEND.EXE, RECOVER.COM, FASTOPEN.EXE, PRINT.COM, FILESYS.EXE, REPLACE.EXE, JOIN.EXE, SUBST.EXE, BACKUP.COM, RESTORE.COM, GRAFTABL.COM, KEYB.COM, SHARE.EXE, EXE2BIN.EXE, GRAPHICS.COM, IFSFUNC.EXE, MODE.COM

ANSI.SYS, COUNTRY.SYS, DISPLAY.SYS, DRIVER.SYS, KEYBOARD.SYS, PRINTER.SYS, RAMDRIVE.SYS, SMARTDRV.SYS, VDISK.SYS, XMA2EMS.SYS, XMAEM.SYS, FLUSH13.EXE

make               # build everything
make test          # kvikdos integration tests (fast)
make deploy        # create out/floppy.img
./run-qemu.sh      # boot interactively in QEMU

Full E2E test targets:

make test-sys
make test-help-qemu
make test-format
make test-backup-restore
make test-diskcomp-diskcopy
make test-share-nlsfunc-exe2bin
make test-append
make test-label
make test-fdisk
make test-recover
make test-assign-subst-join
make test-debug-qemu
make test-drivers-qemu
make test-misc-qemu
make gen-checksums   # regenerate tests/golden.sha256 (run make clean first)

Linux

sudo apt install nasm gcc make python3 qemu-system-x86 mtools

macOS

brew install nasm gcc make python3 qemu mtools

• MS-DOS/ — fork of microsoft/MS-DOS (dos4-enhancements branch)
• kvikdos/ — fork of pts/kvikdos with DOS 4.0 compatibility stubs and macOS support
• bin/ — wrapper scripts invoking kvikdos for each DOS tool (masm, cl, link, lib, …)
• mk/ — per-module Makefile fragments
• Makefile — GNU Makefile orchestrating the full build
• tests/ — all test scripts (kvikdos E2E, QEMU serial, golden checksums, /? smoke tests)
• KEYNOTES.md — build notes, architecture decisions, tips and tricks
• TODO.md — current work in progress