2K Linux

A Linux distribution that was supposed to bootstrap from a 2 kilobyte binary (and a pile of source code).

Current status: a Forth system that reads its source from FAT32, and chunks of a C preprocessor.

Deprecation warning

After a while, I realized that this approach is not ideal, because while booting from source code fully automatically makes for a nice demo, it doesn't have any way of inspecting what happens along the way, which is the reason bootstrapping is appealing.

I am currently approaching this problem from another angle with miniforth, which has the added benefit of a seed binary that's only 512 bytes, and enables interactive development with nothing else on disk.

Testing

You'll need:

• yasm or nasm
• mtools
• bash
• sfdisk
• GNU coreutils
• an emulator like QEMU or bochs if you are not brave enough to run it on hardware.

Run the build.sh script to generate a disk image called gen/2klinux.img. You can use the run.sh script to test it under QEMU.

The Forth system

The Forth implemented in 2K Linux is not fully ANS compliant. This section aims to list all places where the implementation diverges from this standard.

• This Forth is not interactive. All input is read from a file on the installation media.
• Input is not read line by line, but in 512-byte sectors. The input buffer might be refilled in the middle of reading a word.
• HERE does not behave like a VALUE, but like a VARIABLE.
• WORD does not take a separator on the stack. Instead, words may be separated by any whitespace character, i. e. anything with an ASCII value <= 32.
• ABORT is an unconditional "print message and halt". No error code is used.
• ." during interpretation will print a message.
• [COMPILE] is only available before POSTPONE is implemented.
• The following CORE and CORE EXT words are not implemented:
  • <#
  • #
  • #S
  • #>
  • 2!
  • 2@
  • >BODY
  • >NUMBER
  • ABORT"
  • ACCEPT
  • ALIGN
  • ALIGNED
  • BASE
  • CHAR+
  • CHARS
  • DECIMAL
  • DOES>
  • ENVIRONMENT?
  • EVALUATE
  • HOLD
  • MOVE
  • QUIT
  • S>D
  • SIGN
  • SOURCE
  • .(
  • ACTION-OF
  • BUFFER:
  • C"
  • COMPILE, (replaced by ,)
  • DEFER!
  • DEFER@
  • ERASE
  • HEX
  • HOLDS
  • MARKER
  • PAD
  • PARSE
  • PARSE-NAME
  • REFILL
  • RESTORE-INPUT
  • S\"
  • SAVE-INPUT
  • SOURCE-ID
  • TO
  • UNUSED
  • VALUE
• There aren't really any blocks to deal with, but a similar wordset is used to deal with 512 byte sectors on the installation media.
• There is only one block buffer
• The only word from the block wordset that carries the standard semantics is BLK
• LOAD just updates BLK and loads a sector from the disk into the buffer, current input won't be restored on EOF and the data will only be interpreted as Forth only if the control is returned to the interpreter. When using LOAD, care must be taken to make sure >IN and LENGTH reflect the reality.
• FILE is a word that takes a pointer to a filename and its length, finds the file on disk and LOADs its first sector. The currently loaded sector is used as the current directory.
• ROOT loads the root directory, to be followed by FILE.