The Commodore 1551 was a floppy disk drive for the Commodore Plus/4 home computer. It resembled a charcoal-colored Commodore 1541 and plugged into the cartridge port, providing faster access than the C64/1541 combination. Commodore reportedly planned an interface to allow use of the 1551 with the C64, but it was never released.
The 1551 is much less common than other Commodore disk drives. The 1541 was always more readily available because it was compatible with the popular C64 and VIC-20, so many people opted to use 1541s with the Plus/4. Since the 1551 was compatible only with the Plus/4, which was a poor seller in the United States, few were made. In Europe, the Plus/4 was much more successful, but because tape drives were the most popular storage device in Europe in the 1980s, the 1551 was not very popular in Europe either.