CASTALIA-ONLY SIGN-ON
The FreeDOS kernel is rebuilt from source so its boot banner reads CASTALIA DOS 386SX Edition. No “FreeDOS kernel”, no “Open Watcom”, no scrolling licence wall.
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TS-SYS-03 // FreeDOS · 386SX EDITION
Castalia DOS
CASTALIA DOS is a practical, beautiful, game-focused DOS-compatible operating environment for real 386 hardware. It is built on the FreeDOS kernel and shell and wraps them in an original suite of tools, eight boot profiles, a game launcher, an installer and a dignified 80×25 text-mode identity drawn from the stone fortresses of the Valencian coast.
A Mediterranean fortress for your 386.
IN DEVELOPMENT · OPEN SOURCEFreeDOS · 386SX+VS MS-DOS 6.22
8BOOT PROFILES
386SXMIN CPU
80×25TEXT MODE
0MS CODE
FREE · OPEN SOURCE
IBM5153
BOOT BANNERThe keep rises · the amber lights up · three seconds
SWITCH CHANNELS TO SEE MORE01 // WHAT IT IS
The system, no marketing
There is no shortage of ways to run DOS in 2026. What there is a shortage of is a DOS that treats a 30-year-old machine as something worth dressing well. Most retro-DOS setups are a pile of drivers and a bare C:\> — functional, and completely anonymous. CASTALIA DOS starts from the opposite instinct: a real 386, booted on purpose, deserves a first-class, coherent, dignified face.
Its identity comes from the stone fortresses of Valencia and Castellón — Peñíscola on its sea-rock, Morella on its hill, the keep of Sagunto. When a Castalia machine powers on, the three-tower keep rises, the CASTALIA DOS wordmark lights amber, stars twinkle over a Mediterranean-blue field, and within about three seconds the menu is ready. Every screen — the boot banner, the rescue disk, the installer, the main menu — wears the same face.
And one rule governs everything else: compatibility beats elegance. When a choice must be made between a prettier design and a game that actually runs, the game wins. That is why the launcher unloads itself from memory before a game runs, and why there are eight memory profiles instead of one clever guess.
Someone decided a 386 deserved a fortress — and then built it. Legally, testably, and beautifully.
02 // WHAT IT DOES
What you can do with it
THE FORTRESS KEEP
An animated splash: a three-tower keep rises, the wordmark lights amber, the pennants and lit windows flicker like candlelight and stars twinkle over the Mediterranean-blue field. Any key skips it; it never blocks the boot.
EIGHT MEMORY PROFILES
A clean menu at boot: Maximum Compatibility, XMS Gaming (default), EMS Gaming, CD-ROM Gaming, Windows 3.x, Diagnostics, Safe Mode and a plain command prompt. Each tuned to the task.
A LAUNCHER THAT STEPS ASIDE
The launcher (LAUNCH) and the menu unload from memory before a game runs, so the game gets every free byte. The elegance is in service of the machine, never the other way around.
THE TOOL ARMORY
MEMPROF, SETSOUND, HWINFO, CFGEDIT, SAFEBOOT, CASTFM, CASTDOC, CASTMARK, CASTEDIT, HELP… a full text-mode suite. Plus minigames: Snake, 15-Puzzle, Almena and Minas.
INSTALLER + RESCUE
A SETUP wizard that never partitions or formats on its own, backs up any file it replaces and changes nothing until you confirm. The 1.44 MB floppy is both the installer and a self-contained emergency boot/rescue disk.
A DIGNIFIED VOICE
Calm, complete sentences; never blames the user, never shouts. “The drive is not ready. Insert a disk and press R to retry” — not “Not ready reading drive A. Abort, Retry, Fail?”.
LEGALLY CLEAN
Zero Microsoft material — no code, binaries, message text or branding. FreeDOS used under its own licence with source shipped, and the copyleft carefully contained.
// THE PRACTICAL HEART
Eight gates into the fortress
1Maximum CompatibilityHIMEM only. The most free conventional RAM.
2XMS GamingDEFAULTHIMEM + UMBs, no EMS page frame.
3EMS GamingHIMEM + EMS page frame + UMBs.
4CD-ROM GamingCD-ROM stack + sound + UMBs.
5Windows 3.xEMS + a SmartDrive-style cache.
6DiagnosticsBoots, then runs the hardware report.
7Safe ModeBare kernel, no drivers, for repair.
8Command PromptNo menu. Just a prompt.
03 // REAL SCREENSHOTS · 386SX EDITION
The boot experience, exactly as the hardware paints it
04 // ARCHITECTURE
How it's built inside
01
AGGREGATION, NOT A FORK
Original Castalia programs run on top of an open-source DOS, talking to it only through the documented INT 21h interface. Nothing Castalia is linked into the kernel or shell.
02
FREEDOS KERNEL + FREECOM
The FreeDOS kernel (KERNEL.SYS) and FreeCOM (COMMAND.COM): a legal, open-source, MS-DOS-compatible DOS. On top: ~20 original 16-bit real-mode programs.
03
BARE-METAL TEXT MODE
VGA 80×25, 16 colours, drawn by direct video-memory writes for speed on a 386SX; BIOS for the cursor and INT 16h for the keyboard.
04
C89 WITH NO HEAP
The whole Castalia layer is real-mode C89, large model, no dynamic allocation: it compiles small and loads fast on period hardware. FAT12 on floppy, FAT16 on disk/CompactFlash.
// HONEST ENGINEERING, IN THE OPEN
It doesn’t just compile: on every commit, a real disk boots in an emulator
01
Repository gate
C89 syntax check of every source, shell-script linting and repository sanity checks.
02
Host unit tests
The real shared modules — INI parser, the boot-banner rebrand tool — compiled and executed natively.
03
16-bit DOS build
All ~20 tools built for real with Open Watcom and verified as genuine DOS MZ executables; the FreeDOS kernel rebuilt with the CASTALIA sign-on.
04
End-to-end boot test
A bootable 1.44 MB floppy image is assembled and actually booted in a headless emulator, asserting it reaches AUTOEXEC.BAT from cold.
SPECIFICATIONS · Full spec sheet
- PLATFORM
- Real 386SX → 386DX · 486 · early Pentium
- MINIMUM
- 386SX · ~640K conventional RAM · VGA
- STORAGE
- 1.44 MB floppy · IDE · CompactFlash
- FILESYSTEMS
- FAT12 (floppy) · FAT16 (disk/CF)
- DISPLAY
- VGA 80×25 text · 16 colours
- AUDIO
- PC Speaker · AdLib · Sound Blaster / Pro / SB16
- INPUT
- Keyboard · serial (COM) or PS/2 mouse
- VERIFIED ON
- Headless DOSBox in CI · 86Box · real hardware: phase 7, pending
- BUILT WITH
- FreeDOS · Open Watcom V2 · NASM · mtools
- LICENSE
- Castalia MIT · FreeDOS GPLv2+ (with source)
// FOUNDATION & LICENSING
Legally clean by construction
CASTALIA CODEMIT
The ~20 tools, the UI toolkit, the boot profiles, the installer and configuration.
FREEDOSGPLv2+
The kernel and FreeCOM shell, memory managers and base utilities. The build fetches them from their upstream sources into third_party/; the design repo does not commit them.
MICROSOFT0 bytes
No code, binaries, message text or branding. Lawfully redistributable worldwide, forever.
ATTRIBUTIONHonest
FreeDOS credited in the shipped source, in the licence tree and on the system’s own About screen.
CREATED BY · Dave Abellán · Claudio di Castello◆ github.com/Tombatossals-Softworks-LLC/Castalia-DOS
05 // STATUS & ROADMAP
Where it is and where it goes
TODAYPhases 1-5 standing20 original C89 tools compiling and verified with a real MZ header, eight boot profiles, a rebuilt kernel of our own and CI that boots a 1.44 MB floppy on every push. No tagged release yet: the repository has not a single tag.
1.0Tombatossals · targetThe stable release, still ahead: phase 9-10 of the repository roadmap, not a shipped version. Reserved for the legendary giant-hero of Castellón, for when the keep stands on its own.
0.5Morella · targetThe installer — which already exists — and a game-compatibility database that today holds exactly two sample entries. Phase 6 of the roadmap is filling it.
0.2PeñíscolaBoot profiles, the main menu, the game launcher, sound / CD-ROM / mouse.
0.1AlmenaraIt boots. The minimal FreeDOS + Castalia image. 386SX-era simplicity.
// AVAILABILITY
SOURCE ON GITHUB1.44 FLOPPY · BUILT IN CIINSTALLER TO C: / CF · IN THE REPONO TAGGED RELEASE YET
06 // QUESTIONS
Reasonable doubts
No. CASTALIA DOS ships no Microsoft code, binaries, text or branding. It is FreeDOS plus original, MIT-licensed Castalia work. Any “MS-DOS 6.22-compatible behavior” wording is a plain description of behaviour, never a claim of origin.
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