View source for Commodore 4040

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{{Original research|date=April 2023}}}}
{{Infobox information appliance  <!-- https://en.wikipedia.org/wiki/Template:Infobox_information_appliance -->
| name         = Commodore 4040
| title        = 
| image        = Commodore4040.jpg
| caption      = Front view of the Commodore 4040 dual disk drive.
| manufacturer = Commodore Business Machines, Inc.
| type         = Floppy disk drive
| releasedate  = 
| price        = 
| discontinued = 
| media        = 2 × 5¼" double-sided [[floppy disk]] [[Floppy disk format#Single Sided, Double Density|SS SD]]<ref name="ieee">{{Cite web |access-date=2020-04-18 |date=  |title=Early IEEE Disk Drives |url=http://www.zimmers.net/cbmpics/deieee.html |quote=  }}</ref>
| os           = [[Commodore DOS|CBM DOS 2.6]]{{r|ieee}}
| power        = 
| cpu          = [[MOS Technology 6502|MOS 6502]] & [[MOS Technology 65xx|MOS 6504]] @ {{nowrap|1 MHz}}
| memory       = 4&nbsp;KB SRAM (8 × [[Random-access memory#SRAM|2114]]), 10&nbsp;KB ROM (1 × [[Read-only memory#Timeline|6332]], 1 × [[Read-only memory#Timeline|6316]])<ref name="2040DD">{{Cite FTP |access-date=2020-04-22 |date=  |title=2040 SERIES SERVICE MANUAL |url=ftp://ftp.zimmers.net/pub/cbm/schematics/drives/old/4040/2040_CBM_Service_Manual.pdf|quote=  |server=ftp.zimmers.net |url-status=  }}</ref>
| storage      = 170 KB per disk{{r|ieee}}
| connectivity = Parallel [[IEEE-488]]{{r|ieee}}
| dimensions   = 
| weight       = 
| compatibility= [[Commodore PET|Commodore PET/CBM]], 4000-series, 8000-series, [[Commodore CBM-II|B128]]
| predecessor  = Commodore 2040 & 3040
| successor    = [[Commodore 8050]] & 8250
| related      = [[Commodore 2031]] & [[Commodore 1541|1541]]
}}

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 International|Commodore Business Machines]]. It uses a wide-case form, and uses the parallel [[IEEE-488]] interface common to [[Commodore PET|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]] & [[Commodore 1541|1541]] 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 [[Floppy GCR|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]], 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 ==
{{reflist|30em}}
* [http://www.floodgap.com/retrobits/ckb/ Commodore Knowledge Base]

[[Category:CBM floppy disk drives]]
{{Commodore disk drives}}
{{microcompu-stub}}