JiffyDOS is a Disk Operating System (DOS) enhancement which gives your C-64 or C-128 the disk access speed it has always needed. A chip-for-chip replacement for the Kernal ROM in your computer and the DOS ROM in your disk drive(s), JiffyDOS achieves levels of performance and compatibility unmatched by other disk speed-enhancement products. Outstanding speed, solid compatibility with virtually all hardware and software, and a new set of desperately-needed commands and features, gives your system a new lease on life and the power to compete with today’s newer, more-expensive machines.

JiffyDOS should not be confused with Cartridges, Turbo ROMs, Burst ROMs or “Parallel” systems. Ultra-high-speed multi-line serial technology enables JiffyDOS to outperform these products without any of their inherent disadvantages. JiffyDOS leaves all ports on your computer open, works with virtually all software, speeds up PRG, SEQ, REL and USR files, and does not require any extra cabling. Owning JiffyDOS also gives you access to some of the best product support available.

JiffyDOS support is included natively in uIEC and all other sd2iec-based solid state drive solutions for the Commodore. Thus, by installing JiffyDOS in your C64 or C128, you can immediately enjoy all JiffyDOS functionality when using these devices.

Authorized Sales Channels

At this time, authorized JiffyDOS sales channels include (in alphabetical order):

Each licensee is responsible for their own product offering. No other distributors are currently licensed to offer JiffyDOS at this time. Please help us maintain the ability to offer licensed JiffyDOS copies by purchasing from one of the above sales channels.

Licensing Information

Though many people associate JiffyDOS with Creative Micro Designs (known most often as CMD), Mark Fellows actually created the ROM replacement and joined forces with Creative Micro Designs to market and sell the system. When CMD stepped out of the Commodore sales marketplace, the rights stayed with Mark, who set up a royalty agreement with the firm that bought the remaining CMD stock.

JiffyDOS sales continued for some time, but eventually, ROMs became unavailable from the new sales channel. As a result, many people, unable to legally obtain the system, resorted to “burning” their own ROMs from pirated images available online.

As RETRO Innovations started marketing the uIEC drive replacement (which supports the JiffyDOS protocol), the lack of legal JiffyDOS sales proved problematic. Buyers wanted to legally obtain JiffyDOS, which was effectively unavailable. Thus, RETRO Innovations worked for many months to secure a licensing agreement for the ROMs, so they could once again enter the market.

Under the master agreement with Mark Fellows, who continues to hold the JiffyDOS copyright, RETRO Innovations works with additional licensees (listed above) to provide ample access to the solution. Additionally, a few enthusiasts purchase image files from RETRO Innovations and create multi-KERNAL or other value-added solutions. When purchasing from these secondary market sellers, please ask to see proof of JiffyDOS image purchase.

Unfortunately, the historical lack of access to this solution has created the perception that it has fallen into the public domain or is considered “orphanware”, neither of which is correct. Though it can be tempting to download one of the many pirated archives of JiffyDOS images, we continue to encourage the community to support the above businesses and Mark Fellows by obtaining legal copies of JiffyDOS. If you would like to secure licensing to legally offer JiffyDOS in your product, please feel free to contact RETRO Innovations.


Below are the installation guides and manual for JiffyDOS. These are provided free of charge to those already owning JiffyDOS and/or those wanting to understand JiffyDOS commands.

I want to thank David Haynes for scanning some of these documents and Shane Fell for the reproduction of the JiffyDOS overlays. As for the other documents and the searchable manual, I’m trying to track down the scanners/authors to thank them.

Over time, I hope to OCR and re-typeset these documents. If you would like to help with this effort, please let me know. As well, the list of documents is currently incomplete. If you can help with copies of documents not yet in the archive, please let me know.

PLEASE LINK ONLY TO THIS PAGE, as the underlying manual and installation guides may move in the future. With the exception of the overlays, PLEASE DO NOT REHOST THESE DOCUMENTS AT OTHER LOCATIONS.

Frequently Asked Questions

  • Can I utilize JiffyDOS on the Ultimate II?

    • Yes. Customers have noted that settings PH1=140 and PH2=80 work well.