Using DOS on the Atari

So many different DOSes!

As I’ve been learning more about the Commodore 64¹, one big difference that keeps coming up is how the DOS for the C64 is built into the ROM of the 1541 disk drives.

Atari 8-bit computers did not work like that. Instead DOS was loaded from disk. This meant that there could be a lot of different versions of DOS.

The original Atari DOS shipped with the Atari 810 disk drive but it was replaced quickly with Atari DOS II (aka DOS 2). This DOS was single-density and allowed 90K on a 5 1/4” floppy disk.

The way the system was designed, when the Atari was powered on it would check if a disk drive was attached. If there was one, it would load the first byte from the floppy (the boot sector). This would then tell the disk how to boot, which meant loading DOS (or for things such as games, could be told to autoboot the game²).

So to use DOS on an Atari you have to power on the drive first and put a disk with DOS in the drive. Only after you do that should you turn on the computer. You’ll then hear the beeps of DOS being loaded before you get to the BASIC “READY” prompt.

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