In the early days of the Commodore 64, some productivity software called Magic Desk was published. It brought some graphical user interface and productivity software to the Commodore 64 ecosystem.

While the reception was great, development was difficult and only the word processor was ever published. The software was packaged as a cart in order to free up disk for word processing needs such as storing typed documents. However, the format used within the cartridge itself was interesting, pushing the ROM limit to bigger than the usual 16k. This was also done for some other games by developpers such as Ocean Software, but the Magic Desk format resurfaced in recent years as Do-it-yourself carts, with PCBs such as this 512k Magic Desk compatible PCB by msolajic (Solajic) – who kindly made it open hardware.

These carts accept bigger EPROMs – 1024k eproms accept much more software than 512k ones. The additional 74LS-series logic chip is used to handle bank switching internally within the cartridge and expose only what’s needed to the Commodore 64, in addition to the PLA logic the computer already uses. However they require something to boot up – Normally the cartridge software such as the magic desk or a specific game software would be made to handle this. That is pretty much how Ocean Software managed to have very large games on cartridges.

Bundling normal software on MD-compatible carts

What if this large cart isn’t to be used by a single large software, but by multiple smaller ones? That is why the Magic Desk Cartridge Generator was created: to bundle a bunch of smaller software into one binary file and include a boot-up selection menu.

This option permits to push PRG programs to a cart, to combine many into one single cart and use up most of the chip.

It is great to package similar software together and can make a rather useful diagnostic utility cart when paired with several of the programmed described in our diagnostics tools article.

Preparing the Magic Cart binary

The binary is essentially compiled from several programs, ran into the Magic Cart Generator. Magic cart generator is essentially a python script that takes it’s config file and make its magic (pun intended)

The config file can make one or many menu and separate programs into them. It can be animated and have music.

The header of the configuration gives the name, but also the expected size in kilobytes, not in kilobits – the chips are in bytes so a 512 kilobits EPROM can receive a 64 kilobytes binary. If the programs entered into the configuration files are making it bigger than the expected binary size, an error message will be displayed.

The command would run like so

python crtgen.py configfile

and the result would be the binary file as named in the configfile.cfg file.

Burning the EPROM

Either it being a binary magic cart taken from the web or one created using the Magic Cart Generator tool, the process is the same as anything being burnt on EPROM.

If by mistake a larger binary is burnt in a smaller EPROM, only the size that fits into the EPROM will function as expected. Geeks beware.