Commodore 1571
Commodore 1571 floppy drive
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| Manufacturer | Commodore Business Machines, Inc. |
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| Type | Floppy drive |
| Release date | 1985 |
| Introductory price | 300 USD (1985) USD 700 (2017 equivalent) |
| Media | 5¼" floppy disk DS DD using GCR or MFM |
| Operating system | CBM DOS 3.0(128D uses v3.1) |
| CPU | MOS 6502 @ 2 MHz, WD1770 |
| Memory | 2 kB RAM 32 kB ROM |
| Storage | 350-410 kB (GCR and MFM) |
| Connectivity | Commodore proprietary serial IEEE-488 5200 bytes/s |
| Backward compatibility |
Commodore 64, Commodore 128 |
| Predecessor | Commodore 1570 |
| Successor | Commodore 1581 |
The Commodore 1571 is Commodore's high-end 5¼" floppy disk drive. With its double-sided drive mechanism, it has the ability to use double-sided, double-density (DS/DD) floppy disks natively. This is in contrast to its predecessors, the 1541 and 1570, which can fully read and write such disks only if the user manually flipped them over to access the second side. Because flipping the disk also reverses the direction of rotation, the two methods are not interchangeable; disks which had their back side created in a 1541 by flipping them over would have to be flipped in the 1571 too, and the back side of disks written in a 1571 using the native support for two-sided operation could not be read in a 1541.
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 C128D had a 1571-compatible drive integrated in the system unit. A double-sided disk on the 1571 would have a capacity of 340 kB (70 tracks, 1,360 disk blocks of 256 bytes each); as 8 kB are reserved for system use (directory and block availability information) and, under CBM DOS, 2 bytes of each block serve as pointers to the next logical block, 254 x 1,328 = 337,312 B or about 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 2x 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 a custom serial interface (CBM-488), hardware bugs in the VIC-20's 6522 VIA shift register prevented it from working properly.
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