Commodore DOS

Commodore DOS, aka CBM DOS, is the disk operating system used with Commodore's 8-bit computers. Unlike most other DOS systems, which are loaded from disk into the computer's own RAM and executed there, CBM DOS is executed internally in the drive: the DOS resides in ROM chips inside the drive, and is run there by one or more dedicated MOS 6502 family CPUs. Thus, data transfer between Commodore 8-bit computers and their disk drives more closely resembles a local area network connection than typical disk/host transfers.

CBM DOS versions

At least seven distinctly numbered versions of Commodore DOS are known to exist; the following list gives the version numbers and related disk drives. Unless otherwise noted, drives are 5¼-inch format. The "lp" code designates "low profile" drives. Drives whose model number starts with 15 connect via Commodore's unique serial (TALK/LISTEN) protocols, all others use IEEE-488.