ST-DOS

The kernel can be compiled and linked using Open Watcom compiler. The kernel does not make other assumptions about the bootloader than that in the memory address 0xFC15 there must be the BIOS drive number of the system drive, and in the memory address 0xFC1C the 32-bit index of the first logical sector of the boot partition. The kernel can be loaded to anywhere in the memory (as long as the starting point is the beginning of a paragraph) and must be started by doing a far jump to the beginning of the code with offset 0.
ST-DOS-specific features

Changelog:
29. 5. 2025: Fixed STDOUT redirection in COMMAND.COM. 23. 4. 2025: Stability improvements with interrupt handling. 10. 4. 2025: Power saving improvements. 30. 3. 2025: The kernel is now compatible with DOS/32A. 21. 2. 2025: Better int21,ah=44 (ioctl) syscall. 19. 2. 2025: memcpy+memset optimizations for CD-ROM drivers. 19. 2. 2025: The ISO9660 filesystem driver should now support other logical block sizes than 2048 bytes. 13. 1. 2025: FORMAT.COM now detects bad sectors. 2. 1. 2025: Fixed a bug in the EXE loader. 24. 11. 2024: Better out of memory handling. 2. 11. 2024: New version of NETDISK. 1. 11. 2024: Fixed a bug in the TCP/IP stack. It should now detect the DNS server correctly from the DHCP response. 18. 10. 2024: Speed optimizations. 10. 10. 2024: New: NUL device and inheritance flag for file handles. 8. 10. 2024: CON is now an allowed driver name. 30. 9. 2024: Fixed a bug that the command prompt exited when it couldn't redirect the STDIO correctly. 28. 9. 2024: STDIO redirections should now work... 24. 9. 2024: The serial port driver now flushes the hardware input buffer when the settings of a serial port are changed. 19. 9. 2024: Included NETDISK and a new mouse driver in the bootable disk images. 12. 9. 2024: Better critical error handler. 11. 9. 2024: Changed the driver API. Update your drivers! 11. 9. 2024: When accessing optical disks the critical error handler is now called by the CDROM device driver instead of the filesystem driver. 7. 9. 2024: Hardening the kernel and the CD-ROM driver against some very unlikely situations that would otherwise crash the system. 6. 9. 2024: Fixes for the TCP/IP stack. 5. 9. 2024: Support for mounting device files to mountpoints. 31. 8. 2024: The graphical shell now supports advanced power saving features. The POWER driver can be downloaded from the software page. 14. 8. 2024: Better compatibility with filesystems that are created with Linux's mkfs.fat. 11. 8. 2024: DIR listing consumes less than 40 columns. 31. 7. 2024: Bug fixes. 19. 7. 2024: Support for large partitioned hard disks. The 2047 MB limit is gone. 16. 5. 2024: Fixed a problem with drive letters in ISO9660 driver. 23. 4. 2024: Fixed a memory leak in the TCPIP module. The TCP/IP stack is now better bug compatible with some packet drivers. 21. 4. 2024: ISO9660 driver can now be loaded also when the computer does not have optical drives. 7. 4. 2024: Bug fixes, the graphical UI doesn't crash anymore when tiling windows. Better congestion control for the TCP/IP stack. The bootloader now supports booting from a partitioned disk. 1. 4. 2024: Added userspace utilities TREE, DELTREE, DIRFIND (called by COMMAND.COM when DIR /S command is given), XCOPY and ATTRIB. 29. 3. 2024: Bug fixes. 28. 3. 2024: Replaced MMX routines with code that uses 32-bit i386 registers. Symbolic links can now point to device files. 26. 3. 2024: Micro-optimizations. The kernel can now be compiled with MMX support to make calculating 64-bit sector indexes faster. The default build uses 32-bit sector indexes. 23. 3. 2024: The size of the source filesystem is now detected automatically when creating filesystem images from optical disks. Modifying allocation size now changes the owner of the memory block. Bug fixes in CD-ROM drivers. 21. 3. 2024: Better support for installing from a USB storage device. Disk read optimizations. 19. 3. 2024: Fixed one memory bug. 18. 3. 2024: Added DOS syscall 0x26. Interrupt vector 0x22 now points to the program termination address. 16. 3. 2024: Fixed two memory bugs. 13. 3. 2024: Fixed write problems with LBA drives. 10. 3. 2024: Bug fixes 24. 2. 2024: Bug fixes and optimizations 22. 2. 2024: Fixed a bug in the .COM loader. 20. 2. 2024: Bug fixes for KEYB. 15. 1. 2024: Support for different keyboard layouts. 10. 12. 2023: Support for 8 TB ISO9660 filesystems. 10. 11. 2023: The ATAPI CD-ROM code should now work with physical hardware without BIOS support for CD-ROMs. 23. 10. 2023: Symbolic links. 10. 10. 2023: Experimental CD-ROM support. 4. 10. 2023: The filesystem mounter now supports MS-DOS logical partitions. 15. 8. 2023: Write buffer optimizations. 15. 7. 2023: Wildcards for COPY and DEL commands. 8. 7. 2023: The kernel now supports BIOS int 13h enhanced disk drive extensions and hard drives that have a size of 2^64 sectors (which is 8589934592 terabytes when the sector size is 512 bytes). The standard build of the kernel also now works with the original IBM PC and XT. 16. 6. 2023: Bug fixes... 27. 5. 2023: It runs DOOM!

Download sources

Download disk images

Source for the kernel & userland

Last updated: 29. May 2025

Source for the boot loader (can be assembled with NASM)
The bootloader searches for a file named KERNEL.BIN from the root directory of a FAT12/16 filesystem and loads it to memory.

Bootable 1,44 MB floppy image

Bootable USB storage image

Bootable "El Torito" CD image

Bootable 360 kB floppy image

Alternative mirror

md5sums

Features

Support for large disks and 2 GB FAT filesystems
Dynamic disk caching
Dynamic file buffering
Mostly MS-DOS-compatible API - most DOS programs should work
Can create and mount disk images
Calls DOS idle handler (int 28h) also during disk I/O
Symbolic links