In order to keep up with the latest technology, Commodore released the Commodore 1581, an inexpensive 3.5" disk drive compatible with the entire Commodore 64/128 line of computers. The design of this disk drive spelled the end of the "GCR" format, as Commodore simply used the MFM standard in order to take advantage of existing parts on the market. The 1581 is still a gem, however, being capable of both 1571 style speed, while still being backward compatible with the Commodore 64s I/O.
Like all Commodore disk drives, the 1581 is a "smart" device. It includes its own processor, memory, disk operating system. In fact, the relationship between a Commodore computer and it's disk drive resembles more closely two computers on a network than a typical Computer->peripheral relationship. The peripherals on the Commodore serial "network" each had a unique identifying "Unit" number, typically ranging from 8-30. This number identified which physical device was being accessed. When a disk drive contained more than one floppy drive (like the 1572 for instance), you also had to refer to the particular "drive" number you wanted (typically 0 or 1). Single-floppy drives, like the 1581, still had to deal with the legacy of the old IEEE-488 dual drives and the version of CBM DOS with which they were compatible by referring to their single floppy as "drive 0".
Model : 1581 Type : 3.5" Floppy Disk Media : Double Density Capacity : 800K per disk Interface: CBM Serial Bus Dos : CBM DOS 10.0 Notes : "burst" speeds, Demo disk
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