Editing Commodore 1551

{{Short description|External 5 1/4-inch floppy disk drive for the Commodore C-16 and Commodore Plus/4 homecomputers}}{{Infobox computing device
| name         = Commodore 1551
| codename     = SFS481{{r|ComputingHistory}}
| aka          = 
| logo         = 
| image        = Commodore 1551 disk drive.jpg
| caption      = View of a European Commodore 1551 disk drive, showing the connector
| developer    = 
| manufacturer = Commodore Business Machines, Inc.
| family       = Commodore 264 series
| type         = Floppy drive
| generation   = 
| release date  = {{Start date and age|1984}}{{r|C64_wiki}}
| retail availability = 
| lifespan     = 
| price <!--intro--> = {{US$|400}}{{r|C64_wiki}} (1984) {{Inflation|US|399|1984|fmt=eq|r=-2}}
| discontinued = 1986{{r|C64_wiki}}
| units sold    = 
| units shipped = 
| media        = 5.25" [[floppy disk]] Single Sided, Single Density{{r|Commodore_1551}}
| os           = CBM DOS 2.6{{r|Commodore_1551}}
| power        = 
| soc          = 
| cpu          = [[MOS Technology 6510|MOS 6510T]]{{r|198410_1551_UsersGuide|page=86}}
| memory       = {{ubl|2 kB RAM{{r|198410_1551_UsersGuide|page=86}}|16 kB ROM{{r|198410_1551_UsersGuide|page=86}}}}
| storage      = {{val|170|u=kB}}{{r|Commodore_1551}}{{r|198410_1551_UsersGuide|page=86}}
| memory card  = 
| display      = 
| graphics     = 
| sound        = 
| input        = 
| controllers  = 
| camera       = 
| touchpad     = 
| connectivity = TED parallel port{{r|Commodore_1551}}
| currentfw    = 
| platform     = 
| service      = 
| dimensions   = {{convert|97|x|200|x|374|mm|abbr=on|disp=br}}{{r|198410_1551_UsersGuide|page=86}}
| weight       = {{convert|10.5|kg|abbr=on|disp=br}}{{r|198410_1551_UsersGuide|page=86}}
| topgame      = 
| compatibility= {{Hlist|[[Commodore 16]]|[[Commodore Plus/4]]}}
| predecessor  = [[Commodore 1541]]
| successor    = {{Hlist|[[Commodore 1570]]|[[Commodore 1571]]}}
| related      = 
| marketing_target =  
| website      = <!-- {{URL|example.org}} -->
| language     = 
}}

[[Image:Commodore 1551 rear.jpg|thumb|Rear view]]
[[Image:Commodore 1551 connector inside (1).jpg|thumb|Adapter interior]]

The '''Commodore 1551''' (originally introduced as the '''SFS 481''') is a [[floppy disk]] drive for the [[Commodore Plus/4]] [[home computer]]. It resembles a charcoal-colored [[Commodore 1541]] and plugs into the cartridge port, providing faster access than the [[Commodore 64|C64]]/1541 combination. Commodore reportedly planned an interface to allow use of the 1551 with the C64, but it was never released.

Aside from faster access, the drive is very similar to the 1541. Like the 1541, it is a single-sided 170-[[kilobyte]] drive for 5¼" disks, with each disk split into 664 256-[[byte]] blocks available for user data plus 19 blocks for DOS data and directory; the [[file system]] makes each block its own cluster.{{r|198410_1551_UsersGuide|page=86}}

==Hardware==
The disk drive uses [[group coded recording]] and contains an [[MOS Technology 6510|MOS Technology 6510T processor]] as a [[disk controller]]. The 6510T is a specialized version of the 6510 processor used in the C64, and it is only used in the 1551. The DOS limits the number of files per disk to 144 regardless of the number of free blocks on the disk because the directory is of a fixed size, and the file system does not allow for subdirectories. Its DOS is compatible with the 1541, so disks written by one drive can be utilized in the other.

The 1551 has no [[DIP switch]]es to change the drive's device number. If a user added more than one drive to a system, they had to open the case and cut a trace in the circuit board to permanently change the drive's number, or hand-wire an external switch to allow it to be changed externally. It is possible to connect a maximum of two 1551s to one computer.

==References==
{{Reflist|30em|refs=

<ref name="ComputingHistory">{{cite web | title = Commodore 1551 Disk Drive | url = https://www.computinghistory.org.uk/det/32124/Commodore-1551-Disk-Drive/ | date = n.d. | access-date = 2023-09-12 | language = en-gb | work = [[The Centre for Computing History]] | archive-url = https://web.archive.org/web/20230414003019/https://www.computinghistory.org.uk/det/32124/Commodore-1551-Disk-Drive/ | archive-date = 2023-04-14 | df = dmy-all}}</ref>

<ref name="198410_1551_UsersGuide">{{cite book | title = Commodore 1551 Disk Drive User's Guide | date = October 1984| url = https://archive.org/details/1551DiskDriveUsersGuide/ | language = en-us | access-date = 2023-09-12| publisher = [[Commodore International|Commodore Business Machines]] | via = [[Internet Archive]] | df = dmy-all}}</ref>

<ref name="Commodore_1551">{{Cite web | access-date = 2023-09-12 | title = Commodore 1551 Disk Drive | last1 = Zimmerman | first1 = Bo | date = n.d. | work = Zimmer's.net | url = https://zimmers.net/cbmpics/d1551.html |archive-url = https://web.archive.org/web/20221008023822/https://zimmers.net/cbmpics/d1551.html | archive-date = 2022-10-08 | url-status = live | df = dmy-all }}</ref>

<ref name="C64_wiki">{{Cite web | access-date = 2023-09-12 | date = 2021-10-13 | title = Commodore 1551 | work = C64-Wiki | url = https://www.c64-wiki.com/index.php?title=Commodore_1551&oldid=35453 | archive-url = https://web.archive.org/web/20230912154751/https://www.c64-wiki.com/index.php?title=Commodore_1551&oldid=35453 | archive-date = 2023-09-12 | url-status = live | df = dmy-all }}</ref>

}}

==Further reading==
{{refbegin}}
*{{cite book | title = Commodore 1551 Disk Drive User's Guide | date = October 1984| url = https://archive.org/details/1551DiskDriveUsersGuide/ | language = en-us | access-date = 2023-09-12| publisher = [[Commodore International|Commodore Business Machines]] | via = [[Internet Archive]] | df = dmy-all}}
*{{Cite web | access-date = 2023-09-12 | date = 2021-10-13 | title = Commodore 1551 | work = C64-Wiki | url = https://www.c64-wiki.com/index.php?title=Commodore_1551&oldid=35453 | archive-url = https://web.archive.org/web/20230912154751/https://www.c64-wiki.com/index.php?title=Commodore_1551&oldid=35453 | archive-date = 2023-09-12 | url-status = live | df = dmy-all }}
{{refend}}

{{Commodore disk drives}}
[[Category:CBM floppy disk drives]]