Commodore 1581
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The Commodore 1581 is a 3½ inch double sided double density floppy disk drive made by Commodore Business Machines (CBM) primarily for its C64 and C128 home/personal computers. The drive stores 800 kilobytes using an MFM format different from both DOS (720 KB), and the Amiga (880 KB) formats. It was released in the summer of 1987 and quickly became popular with bulletin board system (BBS) operators and other users.
Like the 1541 and 1571, the 1581 has an onboard MOS Technology 6502 CPU with its own ROM and RAM, and uses a serial version of the IEEE-488 interface. Inexplicably, the drive's ROM contains commands for parallel use, although no parallel interface was available. Like the 1571, it can read various other disk formats using special software. This capability was most frequently used to read MS-DOS disks. However, unlike the 1571, which is nearly 100% backward-compatible with the 1541, the 1581 has limited compatibility with Commodore's earlier drives. Although it responds to the same DOS commands, most disk utilities written prior to 1987, most notably fast loaders, are 1541-specific.
The 1581 added support for partitions, but this was largely unused. It implements faster burst mode access than the Commodore 1571 5¼" drive. The 1581 provides a total of 3160 blocks free when formatted (a block being equal to 256 bytes). The number of permitted directory entries was also increased, to 288 entries. With a storage capacity of 800 KB, the 1581 was the highest capacity serial bus drive ever made by Commodore (the 1 MB SFD-1001 used the parallel IEEE-488), and the only 3½" one. However, starting in 1991, Creative Micro Designs (CMD) made the FD-2000 high density (1.6MB) and FD-4000 extended density (3.2MB) 3½" drives, both of which offered not only a 1581 emulation mode but also 1541 and 1571 modes.
Utilities to read 1581-formatted disks in standard PC floppy drives under Linux or Microsoft Windows exist.
[edit] Specifications
- Onboard CPU: MOS Technology 6502 @ 2 MHz
- RAM: 16 KB
- ROM: 32 KB
- Transfer protocols: standard and fast serial; burst mode; and commands for parallel interface (the latter not used)
- Disk type: 3½ inch
- Storage format: MFM, double density, double-sided
- Interface: CBM's proprietary 'serial IEEE-488'
This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.
 Floppy disk drives for Commodore 8-bit systems |
|
| 8" IEEE: | 8020 |
| 5¼" IEEE: | 2031 • 2040 • 3040 • 4031 • 4040 • 8050 • 8250 • SFD-1001 |
| 5¼" serial: | 1540 • 1541 • 1551 • 1570 • 1571 • 1572 • MSD SD |
| 3½" serial: | 1581 • CMD FD |
