Editing Commodore PET (section)

===Peripherals===
[[File:CBM8028-2.png|thumb|right|Commodore 8028 daisy wheel printer]]
:[[Commodore 2031]] single disk drive ({{nowrap|170 KB}} single-sided 5.25-inch format)
:Commodore 2040/3040 dual disk drives{{snd}} The initial dual floppy disk drive units. 2040 (U.S.), 3040 (Europe). ({{nowrap|170 KB}} single-sided 5.25-inch format)
:Commodore 4022 [[dot matrix printer]], [[tractor feed]], with [[Epson]] mechanicals.<ref>[[:File:Cbm4022p-2.jpg]]</ref>
:Commodore 4023 dot matrix printer, tractor feed, with Epson mechanicals.<ref>[[:File:Cbm-4023.jpg]]</ref>
:[[Commodore 4040]] dual disk drive{{snd}} replacing the 2040 and 3040 models; used same disk format as the 2031 and could be used as a stand-alone disk copier
:Commodore 8024 132 column printer, friction or traction gear, with [[Mannesmann Tally]] mechanicals
:Commodore 8028 daisy wheel printer, 40 chars/s, friction or traction gear, with [[Kombinat Robotron|Robotron]] mechanicals
:[[Commodore 8050]] dual disk drive ({{nowrap|500 KB}} single-sided 5.25-inch format)
:Commodore 8075 plotter, with [[Graphtec Corporation|Watanabe]] mechanicals
:[[Commodore 8060]] single 8-inch disk drive (single-sided 800K format, also supports IBM 3740 disks)
:[[Commodore 8061]] dual 8-inch disk drive (single-sided 800K format, also supports IBM 3740 disks)
:[[Commodore 8062]] dual 8-inch disk drive (double-sided 1.6MB format, also supports IBM 3740 disks)
:[[Commodore 8250]] "quad density" dual disk drive ({{nowrap|1 MB}} capacity, same as the 8050, but double-sided)
:[[Commodore 8280]] dual disk drive (8-inch) ({{nowrap|500 KB}} [[Modified frequency modulation|MFM]] format)
:[[Commodore D9060|Commodore 9060]] hard drive (5&nbsp;MB)
:[[Commodore D9060|Commodore 9090]] hard drive (7.5&nbsp;MB)
:[[Commodore SFD-1001]] "quad density" single disk drive (basically a single-drive 8250 model)

The original lineup of disk drives for the PET were the single-unit 2031 and dual-unit 2040, 3040. Then followed the 4040, 8050, and 8250. Later (near the end of the PET's lifespan), single-unit 2031 and SFD-1001 drives were produced that used the same case as the 1540/1541, but sported the PET's parallel interface instead of the VIC-20/C64 [[Commodore bus|IEC serial]] interface. The 4040/2031 used the same {{nowrap|170 KB}} format as the [[Commodore 1541|1541]] and is read compatible (although software that performs low-level drive access will not work, and a one byte sector–header size difference makes the formats write-incompatible). 8050 and 8250 drives had an incompatible higher density {{nowrap|500 KB}}/{{nowrap|1 MB}} format, but were popular well into the 1980s as server/[[Bulletin board system|BBS]] storage devices because of their large capacity.

In addition, Commodore had 8-inch 8060, 8061, 8062, and 8280 drives which used [[modified frequency modulation|MFM]] encoding instead of the [[group coded recording|GCR]] used on their other disk drives and was mainly intended to allow PET users to read disks written on IBM mainframes/[[minicomputer]]s. {{nowrap|5 MB}} and {{nowrap|7.5 MB}} hard disks were produced as well. They have no [[Directory (computing)|sub-directory]] support and are treated as simply a larger floppy disk.

All PET peripherals will work on VIC-20/C64/Plus-4/C128 machines with an IEEE-488 parallel to IEC serial adapter (reverse IEC serial to IEEE-488 parallel adapters were also made), and as mentioned above, using these adapters, 8050/8250 drives were sometimes used on C64s for [[bulletin board system|BBS]] service because of their large capacity and faster interface.

An alternative option for adding floppy disk capability to the PET was the Computhink disk system.<ref name="compute2">{{cite web|url=http://www.commodore.ca/gallery/magazines/compute/Compute-002.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.commodore.ca/gallery/magazines/compute/Compute-002.pdf |archive-date=2022-10-09 |url-status=live|title=Compute - The Journal of Progressive Computing - 002|page=19|date=January–February 1980|access-date=2013-04-26}}</ref> Although references to this system are hard to find today, it was nevertheless popular at the time, as it was both cheaper and considerably faster than the Commodore system and available from an earlier date. Unlike the Commodore units, it did not use the IEEE-488 interface, but instead required an extra circuit board to be installed inside the PET, connected to the PET's expansion connector, which used a [[Western Digital]] floppy controller chip to provide a standard [[Shugart bus|Shugart]] interface.<ref name="deutschland">{{cite web|url=http://www.forum64.de/wbb3/board13-sonstige-commodore/board16-cbm-rechner/1328-pet-floppyplatine/|access-date=2013-04-26|title=Pet Floppyplatine (in German)}}</ref> The board also held extra RAM for use as a [[disk buffer|disk transfer buffer]], and ROM containing the disk operating software. This software was not compatible with Commodore standards and was somewhat awkward to use. Before using the disk system, it had to be initialized manually by issuing the command SYS45056. This made available a set of "pseudo-BASIC" commands for performing disk operations, which bore little or no resemblance to the standard Commodore commands for the same operations and in addition had to be prefixed with $, thus breaking the rules of BASIC syntax. It had a severe limitation in that it was only possible to have one file open at a time, which made many common tasks difficult and slow, though the direct interface to the motherboard made data transfer significantly faster than the CBM units using the IEEE-488 bus. The additional code hooked into the BASIC interpreter could slow the execution of BASIC programs by 20–30%, and it would break with programs which used the standard POKE to disable user STOPs.{{r|progpet|pp=198–210}} Nevertheless, it was still regarded as a useful system and as a great improvement over cassette storage.