The ever-so-popular EPYX Fast Load cartridge for the Commodore 64 included a DOS wedge (adding commands such as $ to list the files on a disk, /filename to load a file and @ to show the disk error status) and a fast loader that sped up certain disk operations, such as loading files from the disk. There were many other cartridges, KERNAL ROM replacements, etc. with similar functionality.

Are there any freely usable and modifiable open source projects that offer either or both of these functionalities? I'm interested in both pure software solutions (presumably loaded from disk) and solutions that involve hardware so a cartridge could be used. (The Epyx Fast Load had not only the software in ROM, but also special support in the cartridge to allow it to "disappear" after a short time, restoring RAM to the $8000-$9FFF address range so that programs could use it.)

This is intended for use on real hardware as well as emulators, and ideally the software should work with an SD2IEC as well. Also, cross-build from a Linux platform would be greatly appreciated, though this is probably something one could add oneself if the standard build platform were a C64 or something else.

  • I think that "works with SD2IEC" boxes you in to the Jiffy protocol, since that is the only fast serial protocol built-in to the SD2IEC drive firmware, and the SD2IEC does not support custom code on the drive as is done with the 1541 for other fast-loaders.
    – Brian H
    Nov 15, 2019 at 19:19
  • 1
    @Brian Does the Epyx Fast Load cartridge use the Jiffy protocol then? Or does it offer only a DOS wedge and its other utilities when used with with the SD2IEC? I have not tested directly (though I will do so when I get access to the equipment), but The Future Was 8 Bit seems to recommend using the two together.
    – cjs
    Nov 15, 2019 at 23:30
  • 1
    I was incorrect. Reviewing the SD2IEC source code from GitHub shows that it supports at least one version of Epyx FastLoad cart protocol, as well as a number of other fast loaders besides Jiffy. Of course, any particular SD2IEC device may or may not support that feature, but I'm guessing most do. The code is over 7 years old.
    – Brian H
    Nov 16, 2019 at 15:56
  • 1
    @Thorbjørn Actually, much of the early microcomputer community was also open source (consider all those early non-commerical CP/M programs); it was somewhere around '79 or '80 I noticed a lot of non-commericial developers were no longer releasing source.
    – cjs
    Jan 17, 2020 at 7:36
  • 1
    would this resource be of help ? c64brain.com/wp-content/uploads/2018/11/… Dec 24, 2022 at 23:36

3 Answers 3


Here are the ones I've come across:

  • SDOS V1.1, a "C64 disk utility and speed loader," which has had development done on it as recently as 2019. According to the readme, it's "Public Domain: open-source and freeware." It's based on earlier programs "VDOS" (1986), "SJLOAD (v0.96)" (2008-2009) and "SDOS (v1.0)" (2016).

    I discovered it on csdb.dk, but the original source seems to be http://istennyila.hu/stuff/sdos.zip.

    I've not yet had time to try it out (perhaps someone else can provide a better answer describing it), but it seems to include fast loaders for both "Jiffy protocol" drives and others, and a simple wedge.

  • SJLOAD: Fast loader only; no wedge. Works only with JiffyDOS-enabled drives (including the SD2IEC). The source SJLOAD.ASM is included on the SJLOAD.D64 image (download) and also viewable on the C64 Wiki. It's based on VDOS, a disassembly of which is also included in the image as VDOS.ASM. Sounds like it's got some bugs ("incomplete," it's described as) and it's no longer under development by the original author.


There's a recent improvement in C64 fast loading technology made by Linus Åkesson. The main idea is to decode GCR inside 1541 thus gaining more transfer speed.

An introductory article into the problems of GCR decoding inside 1541 (with the memory for both code and data of just 2048 bytes) is here: https://www.linusakesson.net/programming/gcr-decoding/index.php. The main idea there is to have wiser tables and faster code that uses heavily many undocumented 6502 instructions.

The complete fastloader, with the sources included, is here https://www.linusakesson.net/software/spindle/v2.php.

  • i love that someone did this recently. stellar.
    – Joe
    Nov 15, 2019 at 23:44
  • (ok, where "recently" = 2013, but still)
    – Joe
    Nov 16, 2019 at 0:35
  • 6
    @Joe I think that six years ago qualifies as "recent" for an item released 37 years ago and discontinued 25 years ago. :-)
    – cjs
    Nov 16, 2019 at 10:11

There is an open-source C64 ROM replacement project in development: https://github.com/MEGA65/open-roms. It contains a DOS Wedge, it can also use JiffyDOS and DolphinDOS protocols to communicate with the drive.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .