Nope you're not mistaken. All Atari 8 bit computers require a DOS (Disk Operating System) to load into the computer before they can access disk drives (unless a software on the disk already has disk operating code embedded in it). Before they can be used, disks (floppies) need to be formatted. Here's a short explanation of the boot process:
- Insert a DOS diskette into your drive (drive id must have been set to 1 in order to boot the computer)
- Turn the drive ON
- Turn the computer ON.
- The first 3 sectors of the disk is read from the inserted disk. These sectors are called boot sectors and Atari's built-in OS knows how to read the 1st 3 sectors
- Those 3 sectors contain code to locate and load the DOS from the rest of the disk. On a DOS diskette the file loaded is called DOS.SYS
- When DOS is loaded, you now have a disk manager who knows how to access disks with directory structures and control is returned to the built-in BASIC and a READY prompt appears on your screen.
- If the Atari doesn't have built-in BASIC (like Atari 400/800/1200XL computers), then a file called DUP.SYS is loaded from the disk next. This is the DOS Menu or Disk Utility Program.
- If the computer does have built-in BASIC (or a BASIC cartridge was inserted in the cartridge slot), the DOS menu can be loaded manually by typing DOS from BASIC'S READY prompt.
- If there is no disk drive attached to the computer DOS is not loaded and the computer boots into BASIC. In this case you can not do any disk operations with the computer until you reboot with a DOS disk attached.
- If no disk drive is present and there is no built-in/cartridge BASIC in the computer, the computer will either land into a Self-Test mode screen (XL/XE computers), to a blank screen called Memopad (400/800) or to an animated Atari logo screen (1200XL)
- Once the DOS is loaded you can then do all sorts of I/O from BASIC, or save/load files, format disks from the DOS menu.
This is the basic workflow of the boot process of Atari 8 bit computers. There are some more details of course but I don't have a reference to a complete documentation at this time.