The Commodore 4040 is the replacement for the previous models 2040 (U.S.) and 3040 (Europe). It's a dual-drive 5¼"
floppy disk subsystem for
Commodore Business Machines
Commodore International (other names include Commodore International Limited) was an American home computer and electronics manufacturer founded by Jack Tramiel. Commodore International (CI), along with its subsidiary Commodore Business Mach ...
. It uses a wide-case form, and uses the parallel
IEEE-488
IEEE 488 is a short-range digital communications 8-bit parallel multi-master interface bus specification developed by Hewlett-Packard as HP-IB (Hewlett-Packard Interface Bus). It subsequently became the subject of several standards, and is ...
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 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 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 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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