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Using JiffyDOS

The advantage of JiffyDOS is that you can load files from the simulated 1541 disk drive (*.d64 files) significantly faster. It also works with real hardware disk drives that you attach via the MEGA65's IEC port as long as you have installed the JiffyDOS ROM on those drives, too.

Learn more about JiffyDOS in the C64 Wiki. You will also find download links to the user's manual there. If you want to learn more about JiffyDOS distribution channels and about licensing information then read this article on go4retro.com.

Where and what to buy

JiffyDOS is commercial software. We recommend, that you either buy from Restore-Store (click here) or from RETRO Innovations (click here).

You need to buy and download two ROM images, one for the C64 and one for the 1541. While both shops use the same name for the C64 ROM image, the name for the 1541 ROM image differs:

  • C64 ROM image: JiffyDOS 64 KERNAL ROM Overlay Image

  • 1541 ROM image at Restore-Store: JiffyDOS 1541 DOS ROM Overlay Image

  • 1541 ROM image at RETRO Innovations: JiffyDOS 1541/1541C/1541II DOS ROM Overlay Image

Make sure you double-check the name of what you buy, otherwise you might end up with a ROM variant that is not supported by the C64 core.

The download packages are ZIP archives. Unpack them. For performing the next steps, you only need the *.bin files.

Prepare the files

The C64 for MEGA65 core needs two files to run JiffyDOS and each of them needs to be exactly 16 kB = 16,384 bytes in size. One file is the C64 Kernal ROM jd-c64.bin and one file is the 1541 DOS ROM jd-c1541.bin. Perform the following steps to create these files from the *.bin files you purchased.

C64 Kernal ROM: jd-c64.bin

  1. Download the C64 BASIC ROM basic.901226-01.bin from zimmers.net
  2. Concatenate the C64 BASIC ROM with JiffyDOS: First the BASIC and then JiffyDOS
  3. Make sure that the resulting file is called jd-c64.bin

Example for the macOS and Linux terminal

The following commands assume that you are in a folder that is empty with the exception of one file that is called JiffyDOS_C64_6.01.bin.

wget http://www.zimmers.net/anonftp/pub/cbm/firmware/computers/c64/basic.901226-01.bin
cat basic.901226-01.bin JiffyDOS_C64_6.01.bin > jd-c64.bin

Example for the Windows command prompt

The following command assumes that you are in a folder that contains the following two files: JiffyDOS_C64_6.01.bin and basic.901226-01.bin.

copy /b basic.901226-01.bin+JiffyDOS_C64_6.01.bin jd-c64.bin

Hint: Do not omit the /b (for binary) in the copy command above.

C1541 DOS ROM: jd-c1541.bin

The JiffyDOS download package contains two *.bin files. Take the one that is exactly 16 kB = 16,384 bytes in size and rename it to jd-c1541.bin.

Install and use JiffyDOS

  • Make sure the core is not started (for example: switch off the MEGA65)

  • Make sure you have a /c64 folder on the SD card that is active, when the C64 for MEGA65 core boots. Remember, that the SD card slot on the back of the MEGA65 takes precedence over the SD card slot at the bottom.

  • Copy jd-c64.bin and jd-c1541.bin to the /c64 folder of your SD card.

  • Start the core with the updated SD card

  • Select "JiffyDOS" in the "Kernal" submenu of the core's menu

  • If you want the core to remember that you seleced JiffyDOS next time you start the MEGA65, make sure that you that you also have the config file c64mega65 installed in your /c64 folder.