Final Cartridge III Undocumented Functions

The “Final Cartridge III” has been among the most popular Commodore 64 extensions, providing a floppy speeder, BASIC extensions, a machine language monior, a freezer and even a (rarely used) graphical desktop. The major advantage compared to other C64 cartridges is the consistent way in which the Final Cartridge III extends the C64 experience.

As it turns out, there are several undocumented instructions implemented in the Final Cartridge III.

Filtered Directory


The DOS”$” command passes all characters following the “$” to the disk drive, allowing the user to specify filters, like this:


This feature is not available for the “@” command in the monitor.

Fast Format


The 26 second fast format known from the “DESKTOP” GUI is also available from the command line. Note that this also works with the “@” command in the monitor. If the ID is omitted, this only overwrites BAM and directory, just like the “N” command.

Disk Rename


This commands renames the disk without erasing it. The ID can be up to 5 characters, so the default “2A” can be overwritten.

FC III ROM Banking


B, followed by a digit between 0 to 3, in the monitor enables the view of the ROMs of the Final Cartridge III. The specified ROM bank will be visible between $8000 and $BFFF. B without a parameter switches the ROM back off.

The following commands in the machine language monitor can be used to dump the complete ROM of an FC3 to disk:

B 0
T 8000 BFFF 8000
S "B0",08,8000,C000
B 1
T 8000 BFFF 8000
S "B1",08,8000,C000
B 2
T 8000 BFFF 8000
S "B2",08,8000,C000
B 3
T 8000 BFFF 8000
S "B3",08,8000,C000

7 thoughts on “Final Cartridge III Undocumented Functions”

  1. Ah, the FC III, had one, too, and was quite fond of it.

    What I never really understood is what the graphical UI was for. It was very limited and as far as I know, there wasn’t really any intended way to add new applications to it.

    I do remember, however, that the box and/or manual of my FC3 showed a screenshot of that UI with applications that simply didn’t exist in my FC3, among them a graph of some sort and I think even a spreadsheet. So either there was some stuff that never made it into the final cartridge (argh, no pun intended 😉 ) or, more likely, it was just a mockup of some sort…

    By the way, has anybody ever had a Final Cartridge II, or I?

    • @Julien: The site I link to has ROMs for all Final Cartridge versions. Personally, I also have an FC 1, which is almost as useful. It doesn’t have the Desktop and the Freezer functionality is very limited, but it seems to have pretty much the same monitor built in. I had to use it recently because I misplaced all my FC3s. 😉

  2. Hmm, I know there was an undocumented BASIC command – I actually got a letter published in Datormagazin with the details that I found when snooping around in the FC3 ROM. Buggered if I could remember what it was though…

    @Julien: You can write your own applications that run on the desktop using the FC3 Developer Disk, that can be downloaded here:

    FC2’s are fairly common, but FC1’s are pretty rare.

    Good tech info can be found here:

  3. JC @ Basic Bytes i have an earlier version fc 3 than you but on that basic page where you were demonstrating those hidden commands you can indeed go direct to monitor press the mouse button on that page and a tskbar appears with a huge number of options just discovered this 1 years after getting the cart—now to dig out my fc1 and see what i can discover there


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