The Commodore 128 and MEGA65 come with built-in features that let them automatically load programs from disk at startup or when issuing a simple boot command. This can make launching C64 games almost as convenient as using a cartridge—without extra hardware.
The latest video from The 8 Bit Theory dives into setting up autoboot on these systems and even briefly touches on the Commander X16. The best part? A single disk image can work across multiple platforms.
How Autoboot Works
Setting up autoboot is straightforward on the MEGA65. The system looks for a file named AUTOBOOT.C65 on the disk and runs it if found. The process is nearly identical on the Commander X16—just change the filename to AUTOBOOT.X16.
The C128 requires a different approach. Instead of scanning for a specific filename, it reads a special sector from the disk to determine if autoboot is enabled. Editing this sector manually requires tools like a disk editor, but there’s an easier way—MakeBoot, a utility that simplifies the process.
Configuring Autoboot on the C128
Using MakeBoot, users can configure their disks without needing deep technical knowledge. The program, developed by MC Bacon (a well-known figure in the C64 community), offers various options, including customizing the boot message, choosing a file to run, and selecting the memory bank.
Once configured, the disk can be used to boot directly into C128 mode. If changes are made later, it may be necessary to reconfigure the boot sector to prevent issues like disk corruption.
Autobooting C64 Games
While autobooting C128 programs is relatively simple, launching C64 games automatically requires a bit more effort. The GO64 command can be embedded in a BASIC program to switch modes, but anything following it is lost after the transition.
To get around this, tools like Etherload (for MEGA65) and 128Boot64 (published in Compute! magazine in 1986) handle the switch while preserving critical data. These programs make the C64 think a cartridge is inserted, allowing it to execute commands automatically.
For the MEGA65, C64Run offers an alternative that takes advantage of the system’s faster loading speeds. Instead of relying on manual commands, it preloads the game before switching modes. This results in dramatically reduced load times—42 seconds drops to just 9 seconds when using burst mode.
Expanding the Approach
The methods above work well for most games, but some titles exceed the default 25 KB loading limit. To support larger games, a workaround using bank switching allows programs up to 30 KB in size to be loaded into memory before switching to C64 mode.
A more advanced technique eliminates the need for cartridge-style memory tricks. Instead of performing a full system reset, a soft switch can transition the machine to C64 mode while maintaining control over execution. This opens up even more possibilities for seamless autobooting.
More Than Just Games
Autoboot isn’t just useful for games. It can also launch programming tools like Turbo Macro Pro or Turbo Pascal directly from disk. On the MEGA65, this method makes it easy to load applications that would normally require a physical cartridge.
For those who want to explore this further, all source code is available on GitHub:
https://github.com/the8bittheory/autoboot65-128/
Final Thoughts
Autobooting on the C128 and MEGA65 streamlines game and software loading, making disks almost as convenient as cartridges. Whether launching a C64 game with minimal effort or loading development tools instantly, these techniques bring a new level of ease to classic computing.
