The Commodore 4040 is the replacement for the previous models 2040 (USA) and 3040 (Europe). It's a dual-drive 5¼" floppy disk subsystem for Commodore International computers. It uses a wide-case form, and uses the parallel version of the IEEE-488 interface common to Commodore PET/CBM computers.
These drive models use a single-density, single-side floppy data storage format similar to that used by the Commodore 1541 drive, but with a slightly different data marker indicating which model originally formatted the disk. The low-level disk format is similar enough to allow reading between models, but different enough that one series of drive models cannot reliably write to disks formatted with one of the other model series.