Commodore 1541: История и эволюция дисковода для C64

External 5 1/4 inch floppy disk drive for the Commodore C64 homecomputer
The early (1982 to 1983) 1541s have a spring eject mechanism (Alps drive), and the disks often fail to release. This style of drive has the popular nickname "Toaster Drive", because it requires the use of a knife or other hard thin object to pry out the stuck media just like a piece of toast stuck in an actual toaster. This was fixed later when Commodore changed the vendor of the drive mechanism (Mitsumi) and adopted the flip lever Newtronics mechanism, greatly improving reliability. In addition, Commodore made the drive's controller board smaller and reduced its chip count compared to the early 1541s (which had a large PCB running the length of the case, with dozens of TTL chips). The beige case Newtronics 1541 was produced from 1984 to 1986.

All but the very earliest non II model 1541s can use either the Alps or Newtronics mechanism. Visually, the first models, of the VIC 1541 denomination, have an off white color like the VIC 20 and VIC 1540. Then, to match the look of the C64, CBM changed the drive's color to brown beige and the name to Commodore 1541. The 1541's numerous shortcomings opened a market for a number of third party clones of the disk drive. Examples include the Oceanic OC 118 a. k. a. Excelerator+, the MSD Super Disk single and dual drives, the Enhancer 2000, the Indus GT, Blue Chip Electronics's BCD/5.25, and CMDs 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 offers 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 uses an external power supply to provide cooler operation and allows the drive to have a smaller desktop footprint (the power supply "brick" being placed elsewhere, typically on the floor). Later ROM revisions fixed assorted problems, including a software bug that causes the save and replace command to corrupt data.

The Commodore 1570 is an upgrade from the 1541 for use with the Commodore 128, available in Europe. It offers 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 1571, the double sided drive. Finally, the small, external power supply based, MFM based Commodore 1581 3½ inch drive was made, giving 800 KB access to the C128 and C64.

The 1541 does not have DIP switches to change the device number. If a user adds more than one drive to a system, the user has to cut a trace in the circuit board to permanently change the drive's device number, or hand wire an external switch to allow it to be changed externally. It is also possible to change the drive number via a software command, which is temporary and would be erased as soon as the drive was powered off. 1541 drives at power up always default to device #8. If multiple drives in a chain are used, then the startup procedure is to power on the first drive in the chain, alter its device number via a software command to the highest number in the chain (if three drives were used, then the first drive in the chain would be set to device #10), then power on the next drive, alter its device number to the next lowest, and repeat the procedure until the final drive at the end of the chain was powered on and left as device #8. Unlike the Apple II, where support for two drives is normal, it is relatively uncommon for Commodore software to support this setup, and the CBM DOS copy file command is not able to copy files between drives – a third party copy utility is necessary. The pre II 1541s also have an internal power source, which generates a lot of heat. The heat generation was a frequent source of humour. For example, Compute! stated in 1988 that "Commodore 64s used to be a favorite with amateur and professional chefs since they could compute and cook on top of their 1500 series disk drives at the same time". A series of humorous tips in MikroBitti in 1989 said "When programming late, coffee and kebab keep nicely warm on top of the 1541." The MikroBitti review of the 1541 II said that its external power source "should end the jokes about toasters". The drive head mechanism installed in the early production years is notoriously easy to misalign. The most common cause of the 1541's drive head knocking and subsequent misalignment is copy protection schemes on commercial software. The main cause of the problem is that the disk drive itself does not feature any means of detecting when the read/write head reaches track zero. Accordingly, when a disk is not formatted or a disk error occurs, the unit tries to move the head 40 times in the direction of track zero (although the 1541 DOS only uses 35 tracks, the drive mechanism itself is a 40 track unit, so this ensured track zero would be reached no matter where the head was before). Once track zero is reached, every further attempt to move the head in that direction would cause it to be rammed against a solid stop: for example, if the head happened to be on track 18 (where the directory is located) before this procedure, the head would be actually moved 18 times, and then rammed against the stop 22 times. This ramming gives the characteristic "machine gun" noise and sooner or later throws the head out of alignment. A defective head alignment part likely caused many of the reliability issues in early 1541 drives; one dealer told Compute!s Gazette in 1983 that the part had caused all but three of several hundred drive failures that he had repaired. The drives were so unreliable that Info magazine joked, "Sometimes it seems as if one of the original design specs must have said 'Mean time between failure: 10 accesses.'" Users can realign the drive themselves with a software program and a calibration disk. The user can remove the drive from its case and then loosen the screws holding the stepper motor that move the head, then with the calibration disk in the drive gently turn the stepper motor back and forth until the program shows a good alignment. The screws are then tightened and the drive is put back into its case. A third party fix for the 1541 appeared in which the solid head stop was replaced by a sprung stop, giving the head a much easier life. The later 1571 drive (which is 1541 compatible) incorporates track zero detection by photo interrupter and is thus immune to the problem. Also, a software solution, which resides in the drive controller's ROM, prevents the rereads from occurring, though this can cause problems when genuine errors do occur. Due to the alignment issues on the Alps drive mechanisms, Commodore switched suppliers to Newtronics in 1984. The Newtronics mechanism drives have a lever rather than a pull down tab to close the drive door. Although the alignment issues were resolved after the switch, the Newtronics drives add a new reliability problem in that many of the read/write heads are improperly sealed, causing moisture to penetrate the head and short it out. The 1541's PCB consists mainly of a 6502 CPU, two 6522 VIA chips, and 2k of work RAM. Up to 48k of RAM can be added; this is mainly useful for defeating copy protection schemes since an entire disk track could be loaded into drive RAM, while the standard 2k only accommodates a few sectors (theoretically eight, but some of the RAM was used by CBM DOS as work space). Some Commodore users use 1541s as an impromptu math coprocessor by uploading math intensive code to the drive for background processing.

The 1541 uses a proprietary serialized derivative of the IEEE 488 parallel interface, found in previous disk drives for the PET/CBM range of personal and business computers, but when the VIC 20 was in development, a cheaper alternative to the expensive IEEE 488 cables was sought. To ensure a ready supply of inexpensive cabling for its home computer peripherals, Commodore chose standard DIN connectors for the serial interface. Disk drives and other peripherals such as printers connect to the computer via a daisy chain setup, necessitating only a single connector on the computer itself.

Early copy protection schemes deliberately introduce read errors on the disk, the software refusing to load unless the correct error message is returned. The general idea is that simple disk copy programs are incapable of copying the errors. When one of these errors is encountered, the disk drive (as do many floppy disk drives) will attempt one or more reread attempts after first resetting the head to track zero. Few of these schemes have much deterrent effect, as various software companies soon released "nibbler" utilities that enable protected disks to be copied and, in some cases, the protection removed. Commodore copy protection sometimes fails on specific hardware configurations. Gunship, for example, does not load if a second disk drive or printer is connected to the computer. Similarly Roland's Ratrace will crash if additional hardware is detected. The tape version will even crash if a floppy drive is switched on while the game is running.