Science Fair Project Encyclopedia
The Commodore 1541 (originally called VIC-1541) was the best-known floppy disk drive for the Commodore 64 home computer. The 1541 was a single-sided 170 kilobyte drive for 5¼" disks. The 1541 followed the previous Commodore 1540 (meant for the VIC-20).
There were two versions of the 1541 mechanics. Early models used a drive mechanism made by Alps Electric , distinguishable by its push-down drive door. Later models utilized a drive mechanism manufactured by Newtronics (Mitsumi), which used a lever release. All but the very earliest 1541s can use either the Alps or Newtronics mechanism. Visually, the first models, of the VIC-1541 denomination, had an off-white color like the VIC-20 and VIC-1540. Then, to match the C64, CBM changed the drive's color to brown-beige and the name to Commodore 1541.
Use of "flippy disks" (disks that could be turned over – done by cutting or punching a notch on the left-hand side of the disk, opposite the factory write-protect hole) would give access to another 170KB for every floppy disk. Each side, of 170KB, was split into 664 256-byte 'blocks'; the file system made each block its own cluster.
The disk drive used Group Code Recording and contained a 6502 processor as a disk controller. The number of sectors per track varied from 17 to 21 (an early implementation of Zone Bit Recording). The drive's built-in disk operating system was CBM DOS 2.6. Most notably, the DOS limited the number of files per disk to 144 regardless of the number of free blocks on the disk because the directory was of a fixed size, and the file system did not allow for subdirectories. The DOS was also notoriously buggy; its most infamous bug was the so-called
@save bug. The command
save "@filename",8 was supposed to overwrite an existing file. Under unpredictable circumstances, however, it would corrupt the disk.
The drive-head mechanism was notoriously easy to mis-align, and had a tendency to make a 'machine-gun' rattle when out of alignment or when formatting a new disk. Some people even wrote code to vibrate the head at different frequencies to play simple tunes such as Amazing Grace. The most common cause of the 1541's knocking and subsequent misalignment, however, was copy prevention schemes on commercial software.
The 1541 used a bit-serial version of the IEEE 488 parallel protocol. The simple protocol that the built-in DOS used supported only about 300 bytes/s. Some third-party speed-ups, however, could transfer about 4 kilobytes per second over the interface, and some "fast loaders" managed up to 10 kbytes/s. The most common of these third-party products were the Epyx FastLoad, The Final Cartridge , and Action Replay cartridges, which all had machine code monitor and disk editor software on board as well.
Priced at under US$400 at its introduction, the 1541 became widely popular. Although expensive by today's standards, a C64 plus a 1541 cost about $900, while an Apple II with no disk drive cost $1395. The demand caught Commodore by surprise, who struggled to produce the drive in adequate quantities. Failure rates initially were very high, and the drives were virtually impossible to find. The lead editorial in the December 1983 issue of Compute!'s Gazette lamented that of seven drives the magazine had in its editorial offices, four had failed. Eventually the problems subsided and the drive became nearly as widely available as the C64 itself.
The 1541's numerous shortcomings opened a market for a number of third-party clones of the disk drive, a situation that continued for the lifetime of the C64. Well-known clones were the Oceanic OC-118 aka Excelerator+, MSD 's single and dual drives, the Enhancer 2000, the Indus GT, and CMD 's FD-2000 and FD-4000. Nevertheless, the 1541 became the first disk drive to see widespread use in the home and Commodore sold millions of the units.
In 1986, Commodore released the 1541C, a revised version that offered quieter and slightly more reliable operation and a light beige case matching the color scheme of the Commodore 64C. It was replaced in 1988 by the 1541-II, which used an external power supply to provide cooler operation and allow the drive to have a smaller desktop footprint (the power supply "brick" being placed elsewhere, typically on the floor).
The Commodore 1570 was an upgraded 1541 for use with the Commodore 128, available in Europe. It offered MFM capability for accessing CP/M disks, improved speed, and somewhat quieter operation, but was only manufactured until Commodore got its production lines going with the double-sided 1571. Finally, the small, external power supply, MFM-based Commodore 1581 3½" drive was made, giving 800KB access to the C128 and C64. By this time, however, many CBM users had shifted their attention to the 16-bit Amiga, and the 1581 was mostly sold to remaining GEOS users.
- Englisch, Lothar; Szczepanowski, Norbert (1984). The Anatomy of the 1541 Disk Drive. Grand Rapids, MI: Abacus Software (translated from the original 1983 German edition, Düsseldorf: Data Becker GmbH). ISBN 0-916439-01-1.
The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details