Editing Commodore 1571 (section)

== Release and features ==
The 1571 was released to match the Commodore 128, both design-wise and feature-wise. It was announced in the summer of 1985, at the same time as the C128, and became available in quantity later that year. The later [[Commodore 128#C128D|C128D]] had a 1571 drive built into the system unit. A double-sided disk on the 1571 would have a capacity of 340 [[kilobyte|kB]] (70 tracks, 1,360 disk blocks of 256 [[byte]]s each); as 8 kB are reserved for system use (directory and block availability information) and, under {{nowrap|[[Commodore DOS|CBM DOS]],}} {{nowrap|2 bytes}} of each block serve as pointers to the next logical block, {{nowrap|254 x 1,328}} = 337,312 [[byte|B]] or about {{nowrap|329.4 kB}} were available for user data. (However, with a program organizing disk storage on its own, all space could be used, e.g. for data disks.)

The 1571 was designed to accommodate the C128's "burst" mode for faster disk access, however the drive cannot use it if connected to older Commodore machines. This mode replaced the slow [[bit-banging]] serial routines of the 1541 with a true serial [[shift register]] implemented in hardware, thus dramatically increasing the drive speed. Although this originally had been planned when Commodore first switched from the parallel [[IEEE-488]] interface to the [[Commodore bus|CBM-488]] custom serial interface, hardware bugs in the [[VIC-20]]'s [[MOS Technology 6522|6522 VIA]] shift register prevented it from working properly.<ref name="b64notes">{{cite web|title=Binary Dinosaurs - C64 Notes |url=http://www.binarydinosaurs.co.uk/Museum/Commodore/c64/c64notes.php |date=7 April 1994 |access-date=27 June 2013}}</ref>

When connected to a C128, the 1571 would default to double-sided mode, which allowed the drive to read its own 340k disks as well as single-sided 170 kB 1541 disks. If the C128 was switched into C64 mode by typing GO 64 from [[Commodore BASIC|BASIC]], the 1571 will stay in double-sided mode. If [[Commodore 64|C64]] mode was activated by holding down the C= key on power-up, the drive would automatically switch to single-sided mode, in which case it is unable to read 340 kB disks (also the default if a 1571 is used with a C64, [[Commodore Plus/4|Plus/4]], VIC-20, or [[Commodore PET|PET]]). A manual command can also be issued from BASIC to switch the 1571 between single and double sided mode. There is also an undocumented command which allows the user to independently control either of the read/write heads of the 1571, making it possible to format both sides of a diskette separate from each other, however the resultant disk cannot be read in a 1541 as it would be spinning in reverse direction when flipped upside down. In the same vein, "flippy" disks created with a 1541 cannot be read on a 1571 with this feature; they must be inserted upside down.

The 1571 is not 100% low-level compatible with the 1541; however, this isn't a problem except in some software that uses advanced [[copy protection|copy protections]] such as the RapidLok system found on [[MicroProse]] and [[Accolade, Inc.|Accolade]] games.

The 1571 was noticeably quieter than its predecessor and tended to run cooler as well, even though, like the 1541, it had an internal power supply (later Commodore drives, like the 1541-II and the 3½" [[Commodore 1581|1581]], came with external power supplies). The 1541-II/1581 power supply makes mention of a 1571-II, hinting that Commodore may have intended to release a version of the 1571 with an external power supply. However, no 1571-IIs are known to exist. The embedded [[operating system|OS]] in the 1571 was {{nowrap|[[Commodore DOS|CBM DOS]]}} {{nowrap|V3.0 1571,}} an improvement over the {{nowrap|1541's V2.6.}}<ref>{{Cite web |title=Commodore Floppy 1571 - Buy it |url=http://myoldmac.net/SELL-com/Floppydrive1571.htm |access-date=2024-07-14 |website=myoldmac.net}}</ref>

Early 1571s had a bug in the [[Read-only memory|ROM]]-based disk operating system that caused relative files to corrupt if they occupied both sides of the disk.  A version 2 ROM was released, but though it cured the initial bug, it introduced some minor quirks of its own – particularly with the 1541 emulation.  Curiously, it was also identified as V3.0.

As with the 1541, Commodore initially could not meet demand for the 1571, and that lack of availability and the drive's relatively high price (about US$300) presented an opportunity for cloners. Two 1571 clones appeared, one from Oceanic and one from Blue Chip, but legal action from Commodore quickly drove them from the market.

Commodore announced at the 1985 [[Consumer Electronics Show]] a dual-drive version of the 1571, to be called the '''Commodore 1572''', but quickly canceled it,<ref>{{cite web|title=A nostalgic look back at the Commodore 128
|date=December 1985 – January 1986
|access-date=12 January 2013
|url=https://archive.org/stream/info-magazine-09/Info_Issue_09_1985_Dec-Jan_1986#page/n25/mode/2up}}</ref> reportedly due to technical difficulties with the 1572 DOS.  It would have had four times as much RAM as the 1571 (8 kB), and twice as much ROM (64 kB). The 1572 would have allowed for fast disk backups of non-copy-protected media, much like the old [[Commodore 4040|4040]], [[Commodore 8050|8050]], and 8250 dual drives.

The 1571 built into the European plastic-case C128''D'' computer is electronically identical to the stand-alone version, but 1571 version integrated into the later metal-case C128D (often called C128 DCR, for D Cost-Reduced) differs a lot from the stand-alone 1571. It includes a newer DOS, version 3.1, replaces the [[MOS Technology CIA]] interface chip, of which only a few features were used by the 1571 DOS, with a very much simplified chip called 5710, and has some compatibility issues with the stand-alone drive. Because this internal 1571 does not have an unused [[8-bit computing|8-bit]] input/output port on any chip, unlike most other Commodore drives, it is not possible to install a parallel cable in this drive, such as that used by SpeedDOS, DolphinDOS and some other fast third-party Commodore DOS replacements.