6pack

Compressor and linker for Commodore 64 PRG files. Merges PRGs into one self-extracting program, or writes compressed data for your own decompressor. ZX0, LZSA2, ByteBoozer2 and RLE, each with its own 6502 decoder.

Linux x64	6pack-2026.11.06-linux-x64.tar.gz	28 MB
Windows x64	6pack-2026.11.06-win-x64.zip	29 MB

Built 2026-11-06 from 5f792e1. Self-contained: no .NET install needed. SHA256SUMS

Unpack and put 6pack on your PATH. The Windows binary is unsigned, so SmartScreen may warn. --effect custom=file.asm also needs 6asm on your PATH.

Full manual: every mode and option, stream and memory layouts.

Pack

$ cp mandel.kla mandel.prg
$ 6pack sfx demo.prg part2.prg mandel.prg -o demo.sfx.prg
demo.prg+part2.prg+mandel.prg → demo.sfx.prg  (32528 → 4355 bytes, 13.4%)
$ 6pack info demo.sfx.prg
file       demo.sfx.prg  (4355 bytes)
load addr  $0801
end addr   $1901
payload    4353 bytes
type       SFX (BASIC stub: SYS 2061)
algorithm  ZX0
  payload at +297 (4056 bytes compressed):
  compressed   4056 bytes → 32528 bytes  (12.5%)
  commands     1107 total  (393 literal runs, 630 new-match, 84 rep-match)
  literals        393 runs    ·     2420 raw bytes  (7.4% of output)
  new-match       630 matches · offset $0001–$6EB9  · length 2–15553 avg 36
  rep-match        84 matches · length 2–6016 avg 83
  max surplus  28475 bytes

Three PRGs become one file you LOAD and RUN. It decompresses to the original addresses and jumps to the entry point, taken from the input's SYS line unless you give -s.

The result in VICE. 32 KB of program and picture in a 4 KB PRG.

Compare

$ 6pack bench mandel.prg
bench: mandel.prg  (10001 bytes, load $6000)

  algorithm    compressed    ratio  surplus  core
  ------------ ---------- -------- -------- -----
  zx0                3254    32.5%     6749   210
  lzsa2              3544    35.4%     6460   249
  bb2                3390    33.9%     6613   215
  rle                4475    44.7%     5527    74

bench also runs exomizer and pucrunch for comparison if they are installed.

Algorithm	Decoder	Good for
`zx0` (default)	210 bytes	general use, best ratio
`lzsa2`	249 bytes	faster decompression
`bb2`	215 bytes	ByteBoozer2 streams
`rle`	74 bytes	repetitive data, smallest decoder

Modes

Mode	Makes
`sfx`	self-extracting PRG
`chain`	several stages, each decompressing and jumping to the next
`mem`	compressed payload only
`level`	indexed archive for loading data at run time
`source`	6asm source: decoder plus data as `.byte`
`asm`	the decoder alone, as a 6asm include
`info`	inspect a PRG: layout, algorithm, stream stats
`bench`	compare algorithms
`unpack`	back to the original

Options worth knowing

6pack sfx game.prg -a lzsa2             algorithm
6pack sfx game.prg --blank-screen       no badlines, no visible garbage
6pack sfx game.prg --bank 0x34          $01 value on exit
6pack sfx game.prg -x border-cycle      effect while depacking
6pack sfx game.prg -d 0x4000            load elsewhere, no BASIC stub
6pack sfx main.prg music.prg@0xA000     merge, overriding a load address
6pack sfx game.prg --watch --run auto   rebuild on change, launch VICE

Credits

ZX0 by Einar Saukas. LZSA2 by Emmanuel Marty (zlib licence). ByteBoozer2 by David Malmborg (HCL), maintained by Luigi Di Fraia.