Last Updated on April 5, 2024 by Dave Farquhar
The Commodore 8050 disk drive was the second-highest capacity floppy drive Commodore made for its 8-bit computers. It was a dual drive unit that connected to the IEEE-488 bus used on the PET and CBM line of computers. Each drive stored half a megabyte of data on 5.25 inch single sided quad density disks. When you listed the directory on a Commodore equipped with an 8050, the disk read 2102 blocks free. They were marketed for educational and business use.
Commodore CBM 8050 disk drive
The original Commodore CBM 8050 disk drive, originally released in 1982, looks very much like other Commodore dual drive units such as the 4040. It used full height drives made by Micropolis, Tandon, or MPI. Even though it looked almost exactly like other Commodore dual drive units, the media was not forward or backward compatible with the older drives. An 8250 or SFD-1001 drive could read and write 8050 disks, as they were double-sided versions of the same drive.
The quad density disk type didn’t last very long. Two other notable computers that used it were the Digital Equipment Corporation Rainbow, and the Tandy 2000, a pair of quirky early MS-DOS machines that weren’t fully IBM compatible.
Since Tandy found a way to read and write double-density disks on its quad-density drive, theoretically Commodore could have done the same and made the 8050 compatible with the 4040 and 1541. But they didn’t.
By cutting one or more of three jumpers at location UE1, or lifting pins 22, 23, or 24 of the 6532 at UE1, you could assign an 8050 a drive number between 8 and 15. To change to device 9, you would cut the jumper next to pin 24.
HP also used the IEEE-488 bus on its computers. Commodore did not use it on its popular home computers because of the cost. The IEC bus on the Commodore 64, 128, VIC-20, and 264 line is a derivative of the IEEE-488 bus but not compatible with it. To use a Commodore 8050 with a Commodore 64 or 128, you have to get a third party IEEE-488 adapter that plugs into the cartridge port.
Second life
The 8050 and its double-sided bretheren, the 8250 and the SFD, saw a second life in the 1980s as drives for Commodore BBSs. Hard drives for Commodores were very expensive, so BBS sysops coveted the quad-density drives. A sysop could store its message base on a 1541, leaving its quad-density drives available for the file transfer section. Each 8050 disk held more than three times as much as a 1541 floppy.
I knew one BBS operator in St. Louis who ran a Color 64 BBS on a pair of 8050 drives and a pair of SFD-1001s, along with four 1541 type drives. This gave a total of 4.4 megabytes of storage, which was a decent-sized Commodore BBS in 1989.
Rarity
The 8050 isn’t super common, but does turn up more frequently than the 8250 or SFD-1001. It came late in the PET’s service life, and Commodore didn’t promote it very heavily. Commodore BBS owners did covet the 8050s into the late 1980s and beyond, although they preferred the double-sided 8250 drive if they could get one. They do occasionally turn up on Ebay.
Protecto Enterprizes bundled 8050 drives for several years with its B-128 closeout package, one in its line of bundles that dated back to 1980 and the ill-fated Interact home computer.
Quad density disks were never especially common and high density disks quickly overshadowed them. You can format regular double density disks as quad density disks in a Commodore 8050 disk drive, or for that matter, an 8250 or SFD-1001, and it usually works. I don’t recommend it, but if you can’t find quad density disks, this trick allows you to use the drive.
David Farquhar is a computer security professional, entrepreneur, and author. He started his career as a part-time computer technician in 1994, worked his way up to system administrator by 1997, and has specialized in vulnerability management since 2013. He invests in real estate on the side and his hobbies include O gauge trains, baseball cards, and retro computers and video games. A University of Missouri graduate, he holds CISSP and Security+ certifications. He lives in St. Louis with his family.