dos10 — open-source DOS in the browser

Build 86-DOS 1.00 (the genuine ancestor of MS-DOS 1.0, the source of which Microsoft released April 28, 2026) from source, with a JS-native re-implementation of Tim Paterson's SCP 8086 Assembler, and run it in a browser-based 8086 emulator.

Live demo: https://86-dos.berrry.app

Upstream sources (gitignored — fetch with scripts/fetch-sources.sh)

• DOS-History/Paterson-Listings — 86-DOS 1.00 source, PC-DOS 1.00 dev snapshots, SCP ASM 2.43 source. Released by Microsoft 2026-04-28, MIT-licensed.
• microsoft/MS-DOS — v1.25 / 2.0 source for cross-reference. MIT.

Layout

• tools/scpasm.js — JS implementation of the SCP ASM 2.43 dialect.
• tools/core/ — 8086 CPU + memory + IMD disk + nine-vector SCP BIOS shim (STAT/IN/OUT/PRINT/AUXIN/AUXOUT/READ/WRITE/DSKCHG).
• test/boot_smoke.js — Node harness; boots the disk image headlessly and asserts COMMAND.COM reaches its date prompt.
• web/ — browser shell. index.html + main.js wire the CPU+BIOS to a canvas-backed glass-TTY (glass_tty.js) modeling an SCP-era serial VDU (80×24, BS/HT/LF/FF/CR/BEL, blinking block cursor).
• assets/86dos114-tarbell-dd.imd — 86-DOS 1.14 disk image (Tarbell DD).
• build/ — generated binaries (gitignored).
• scripts/fetch-sources.sh — clones the upstream repos into paterson/ and msdos-src/.

Build / run

npm run build:asm    # ASM_2.43.ASM  -> build/ASM.COM       (self-host check)
npm run build:dos    # 86DOS.ASM     -> build/MSDOS.BIN
npm run boot:smoke   # node test/boot_smoke.js              (headless boot)
npm run web          # python3 -m http.server 8000          (open /web/)
npm run deploy       # bundle web/+tools/+assets to Berrry  (needs .env.berrry)

The web shell currently boots the on-disk 86-DOS 1.14 image directly (loader + BIOS read off cyl 0–1; INT 0xE0+idx trampolines patched over the nine BIOS entry points), not the freshly-assembled MSDOS.BIN — that's the next milestone.

Hardware target

Seattle Computer Products S-100 8086 system: serial console, 8" floppy. No video card, no IBM-PC BIOS — that's why the BIOS shim is nine character/disk vectors and the terminal is a glass-TTY rather than a framebuffer. PC-DOS 1.0 was Microsoft's port of this code to the IBM PC hardware in 1981.

Status

Boots to COMMAND v. 1.10 date prompt; line input works. Disk writes, file commands, and assemble-then-boot loop are TODO. See git log.