Commodore Disk Drives
Commodore built numerous floppy disk drives to complement their home computers. All of them connected to the IEEE-488 serial bus with the exception of the Plus/4's 1551 which used the expansion (cartridge) port. This meant that with the exception of the 1551, all floppy drives are interchangeable between the VIC-20, C64, and C128. The C16, 116 and Plus/4 can all use the other drives too.
The use of floppy disks as a storage medium was very much the norm in the United States from the early 1980s, where the price of this technology was relatively inexpensive for home users. In Europe, it was not the case until several years later - audio cassettes were the standard storage medium - games and business software shipped on cassette, and only high-end titles were released in Europe on floppy disk. This meant Commodore's floppy drives didn't sell as well in Europe due to their high price. Towards the latter part of the 1980s more owners adopted floppy drives, and often stored their cassette software on floppy disk for faster retrieval.
Introduced in 1982, this was Commodore's first floppy drive. It supported single-sided 5.25" floppy disks, and was able to store 170 KB. It used Commodore's GCR encoding method. In Germany, this drive was known as the VC-1540 (since the VIC-20 was branded the VC-20). When combined with the VIC-20, it was the lowest-priced computer and floppy drive combo available, and the first ever to sell for an MSRP of under $1000 USD. Ironically, the drive was more expensive to buy than the VIC-20 computer itself.
It is an "intelligent" peripheral in that it has its own MOS 6502 CPU (as in the VIC-20) as well as a DOS held in ROM. This was unheard of in other hom computers, where the DOS was typically loaded in from a boot floppy disk and then executed using the computer's CPU.
The 1540 didn't sell in great numbers, primarily because at the time of the VIC-20 (pre-64), the cost of floppy disks was high, so most software was sold on audio cassette or cartridge. Furthermore, the speed of the drive didn't give much gain on loading software from cassette. Today, these drives are quite rare.
Due to a timing conflict between the C64's VIC-II chip and the 1540, this drive is incompatible with the C64. Due to this issue, the 1541 that launched to replace the 1540 actually ran slower than the 1540 as the revised ROM in the 1541 slowed down the timing of the drive slightly to make it work. Many 1540s had their ROM updated with the 1541 ROM to make it work with the C64.
The 1541, originally called the VIC-1541, was designed to complement the VIC-20 and later on, the Commodore 64. It had an integrated power supply at the rear of the unit, making it very large by floppy drive standards at the time. Like its 1540 forebear, it is an intelligent drive with its own CPU, ROM, and controller logic built-in.
The first 1541 drives produced in 1982 have a label on the front reading VIC-1541 (or VC-1541 in Germany) and have an off-white case to match the colour of the VIC-20. In 1983, the 1541 was switched to having the familiar beige case and a front label reading simply "1541" along with rainbow stripes to match the Commodore 64.
The 1541 was considered brutally slow for its time. This resulted in third party companies introducing "turbo" loaders and entire replacement firmware such as the popular JiffyDOS, which replaced both the DOS ROM in the floppy drive and the Kernel ROM in the C64 or C128. Despite its many shortcomings, it saw widespread use in the home.
These first 1541 drives used a spring-eject mechanism manufactured by Alps Electronics. These can be recognised by the pull-down drive door latch (see picture above), and have a controller board that runs almost the full length of the drive.
A later version of the 1541 used a Newtronics drive mechanism (recognized by the rotating lever to open the drive door) - see picture to side. The drive mechanisms on these were also changed to Mitsumi ones. These later drives are known for being more reliable than the earlier Alps 1541. It also got a smaller drive controller board with fewer chips, making them cheaper to produce. Beige-cased "version 2" 1541 drives were produced from 1984 to 1986.
With the launch of the cosmetically updated Commodore 64 in 1986 in a light beige colour, Commodore also updated the 1541-II floppy drive with the same-coloured casing. These are known as the 1541C, since the Commodore 64 was rebranded the 64C.
The 1541C wasn't just a cosmetic update. It also offered quieter operation and was slightly more reliable. It was succeeded by the 1541-II, launched in 1988.
The 1551 floppy disk drive was designed for use with the Commodore 264 series (C16, 116 and Plus/4). Unlike the 1541, the 1551 plugs into the 264-series cartridge port via an adapter giving it much (3x) faster performance than the 1540/1541. This was a parallel connection rather than serial. It is single-sided and supports the same disk capacities as the 1540/1541 (170 KB per disk side allowing for 664 256-byte blocks).
It is not compatible with the VIC-20, 64 or 128 computers.
In 1988, Commodore released the smaller 1541-II. Still a 5.25" floppy drive, this version had an external power supply brick which reduced internal case temperature of the drive. Prior 1541s got a reputation for running very hot and this was thought to be the main cause of unreliability. The smaller case design also complemented the sleeker-looking Commodore 64 and 128.
A number of bugs came into being with this model which were known to cause corruption of data in some circumstances. Commodore offered later ROM upgrades to fix these.
The 1570 was the first floppy drive designed for use with the Commodore 128. Cosmetically it looked very similar to the 1541C that went before it, but was the first drive to support both GCR and MFM encoding. GCR was the encoding format used by all prior Commodore disk drives. MFM encoding was used by DOS and CP/M operating systems.
It is a single-sided drive supporting 5.25" floppy disks.
The 1571 was Commodore's first [and only] 5.25" double-sided floppy disk drive. Succeeding the 1570 and launched a short time after the Commodore 128 in 1985, it was the new "high-end" floppy drive. It sat lower than the 1541 and 1541C in order to look right next to the cosmetically updated Commodore 64C and Commodore 128. It differed from prior models in that it ran at a higher speed when coupled with the Commodore 128. When used with a C64 (or a C128 in 64 mode) it would run at the old slower speed for compatibility reasons.
As with the previous drives, the 1571 is almost a computer in its own right. It still runs a MOS 6502A CPU running at either 1 or 2 MHz, as well as a 6522 and 6526.
The 1571 has two DIP switches on the rear which allow the setting of the device number. They are:
Device # Left Switch Right Switch
8 Up Up
9 Down Up
10 Up Down
11 Down Down
Commodore continued to manufacture and sell the 1571 until their demise in 1993.
The last floppy drive made by Commodore was the 1581 - a 3.5" double-sided drive.
|Price When New||$400 USD|
|Designed for||VIC-20 and C64||VIC-20 and C64||C16, 116, and Plus/4||C128||C128|
|Encoding||GCR||GCR||GCR||GCR / MFM||GCR / MFM|
|Speed Modes||Slow||Slow||Fast||Slow / Burst||Slow / Burst|
|Transfer Rate||300 bytes / sec||300 bytes / sec||1 KB / sec|
|DOS Version||2.6||3.0 or 3.1||3.0 or 3.1|
|Compatibility||Compatible with 1541||Compatible with 1541||Compatible with 1541|
|CPU||MOS 6502||MOS 6502||MOS 6510T||MOS 6502A||MOS 6502A|
|CPU Speed||1 MHz||1 MHz||1 or 2 MHz||1 or 2 MHz|
|Drive Number Selection||Not possible||DIP switches on rear||DIP switches on rear|
Q: Can I replace the drive mechanism in a 1541 with one from an early PC?
A: Yes! Some 5.25" 360 KB PC floppy drive mechanisms can be transferred to work in a 1541. Someone took a 360 KB TEAC drive from a PC, removed the electronics completely and connected everything to the 1541 board. The only changes necessary were to invert the motor signal and change the stepper motor supply voltage to 5V from the original 12V. The most important point is the type of stepper motor used. Most floppy drives use unipolar motors, but this TEAC one uses a bipoler one, just like the 1541. With other drives an H-bridge stepper driver circuit has to be installed which isn't easy. Due to abundance of 1541 drives (even today), it's probably easier to simply take a replacement mechanism from another 1541.