The Commodore 4040 is the replacement for the previous models 2040 (U.S.) and 3040 (Europe). It's a dual-drive 5ΒΌ"
floppy disk
A floppy disk or floppy diskette (casually referred to as a floppy, a diskette, or a disk) is a type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined with a ...
subsystem for
Commodore Business Machines
Commodore International Corporation was a home computer and electronics manufacturer with its head office in The Bahamas and its executive office in the United States founded in 1976 by Jack Tramiel and Irving Gould. It was the successor comp ...
. It uses a wide-case form, and uses the parallel
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 1540 &
1541
__NOTOC__
Year 1541 ( MDXLI) was a common year starting on Saturday of the Julian calendar.
Events
January–March
* January 4 – Leonardo Cattaneo della Volta is elected to a two-year term as the new Doge of the Republic o ...
drives, but with a slightly different data marker indicating which model 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. A difference of one extra header byte is what causes this write incompatibility.
The
Group Coded Recording (GCR) scheme of binary encoding is used to store data on the magnetic disk medium. The drive also uses variable bit-clock to enable increased data density on a standard single-density floppy disk. It is a form of
constant bit-density recording done by gradually increasing the clock rate (
zone constant angular velocity, ZCAV) and storing more physical sectors on the outer tracks than on the inner ones (
zone bit recording
In computer storage, zone bit recording (ZBR) is a method used by disk drives to optimise the tracks for increased data capacity. It does this by placing more sectors per zone on outer tracks than inner tracks. This contrasts with other approache ...
, ZBR). Starting with the Commodore 2040 drive, this enabled Commodore to fit 170 KB on a standard single-sided single-density 5.25" floppy.
References
Commodore Knowledge Base
CBM floppy disk drives
{{microcompu-stub