The Commodore 4040 is the replacement for the previous models 2040 (U.S.) and 3040 (Europe). It's a dual-drive 5¼"
floppy disk
A floppy disk or floppy diskette (casually referred to as a floppy, or a diskette) is an obsolescent 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 w ...
subsystem for
Commodore Business Machines. 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
The Commodore 1540 (also known as the VIC-1540) introduced in 1982 is the companion floppy disk drive for the VIC-20 home computer. It uses single-sided 5¼" floppy disks, on which it stores roughly of data utilizing Commodore's GCR data enco ...
&
1541
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Year 1541 ( MDXLI) was a common year starting on Saturday (link will display the full calendar) of the Julian calendar.
Events
January–June
* February 12 – Pedro de Valdivia founds Santiago del Nuevo Extremo, whi ...
drives, 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. 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
Constant or The Constant may refer to:
Mathematics
* Constant (mathematics), a non-varying value
* Mathematical constant, a special number that arises naturally in mathematics, such as or
Other concepts
* Control variable or scientific cons ...
recording done by gradually increasing the clock rate (
zone constant angular velocity 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 on inner tracks. This contrasts with other approac ...
, 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 on inner tracks. This contrasts with other approach ...
, 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
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