Commodore 1541 disk drive

The Commodore 1541 disk drive was the most common Commodore 64 floppy drive. Commodore fans from the 1980s loved to hate it. It was the first disk drive priced low enough to gain mainstream acceptance. But it was slow and loud and unreliable.

We put up with it anyway. A home computer was a luxury in those days and most of us had some idea how lucky we were to live through that time and experience it firsthand.

Technical specifications

Commodore 1541 disk drive
The Commodore 1541 disk drive was the most common Commodore 64 floppy drive. If you’re looking for one today, look for one that looks like the drive on the left. The one on the right is more prone to have problems reading disks.

The Commodore 1541 was a single sided, single density floppy disk drive that stored 170K of data on 5.25-inch disks. It works fine with the 360K double-sided, double-density disks popular with the IBM PC and compatibles of the time. The 1541 just uses one side of the disk. Many users would notch the second side and flip the disk over to use the other side. It stored 144 filenames in its directory and each disk had 664 blocks free. A disk block was 256 bytes.

Note that the 1541 won’t work with high-density disks like the IBM PC/AT and later IBM compatibles used. You may be able to coax the disk into working for a while but it won’t work reliably. More likely, the disk won’t even format.

While most commonly used with the Commodore 64, it would work with other Commodore computers, notably the VIC-20, Commodore 128, and Plus/4. It connected via Commodore’s proprietary IEC serial bus, which used a round 8-pin DIN connector. Setting it up isn’t difficult, it’s just different from today.

Life with the Commodore 1541 disk drive

My first computer was a Commodore 64 with a 1541 floppy disk drive. We kept it about two years before upgrading to a 128 with the faster, quieter 1571 drive. We had better luck with our 1541 than some did. Our example was loud and slow, but it didn’t give us any trouble.

Pretty much all 5.25-inch floppy drives from the early 1980s were loud, especially by modern standards. The drive would growl as the drive head performed its seek operation to move to the track it needed, and then it would click audibly from time to time as it read the files. But when you inserted a commercial game with copy protection on it and typed LOAD”*”,8,1 to boot it, toward the end of the load, the drive would click and clack, the red activity light would blink, and the drive would knock repeatedly like a rock’n’roll drum solo.

Someone at Commodore must have liked Iron Butterfly’s song In a Gadda Da Vida, because that’s what it was like every time you wanted to play a game. A 17-minute load time, with an extended drum solo. OK, I exaggerate a bit, because most games took 3-5 minutes to load. But still, that’s a long time when you’re a kid. So it was like the radio edit of In a Gadda Da Vida, unless you hadda da fast loader.

Why Commodore 1541 drive knocks happened

The knocking was because of disk errors game publishers intentionally put on the disks. Disk copiers wouldn’t reproduce the errors, or at least a normal disk copier wouldn’t. So as loading time approached the end, the game would read the part of the disk with the errors. The errors would confuse the drive, which would bang its head up against a piece of metal called a head stop so that it would know where the head was, then it would try reading the error again.

Different games had different errors on them, which caused the drive to knock differently. A connoisseur could learn to recognize what game was being loaded from a different room.

And the knocking did more than just make a lot of annoying noise. Eventually it would damage the drive, requiring the head or the stopper to be re-aligned. The repair got old. Several third parties tried to capitalize on the 1541’s frailties and release clones that were slightly better. Most of them were demonstrably better but most of them also weren’t completely compatible.

Commodore 1541 disk drive variants

Commodore 1541-ii
While the later Commodore 1541-II, first released in 1988, doesn’t have the same iconic look as the earlier variations, it’s also less prone to have problems.

Commodore made millions of 1541 drives, and it changed the design over time. The earliest drives were almost white and matched the color of the VIC-20 rather than the 64. The 1541 was designed for the 64, but the VIC-1540 drive, intended for the VIC-20, was almost identical. The 1540 wouldn’t work with the 64 but the 1541 worked with the VIC-20, so Commodore changed the drive’s part number and reused the existing supply of white-colored 1540 cases. The only difference between a 1540 and the 1541 was the label on the front and the ROM chip inside the drive. The earliest 1541s had a silver label that said “Commodore single drive floppy disk VIC-1541.” Slightly later drives said “Commodore 1541” with the familiar rainbow logo.

Once Commodore used up the supply of old 1540 parts, Commodore started shipping dark beige drives that matched the C-64’s color. Many of these drives had a flip-down drive door, indicative of a drive mechanism made by Alps Electric.

Commodore eventually changed to a drive mechanism made by Neutronics or Mitsumi. This drive did a much better job of staying in alignment, but the drive heads on these drives had a tendency to oxidize over time if someone used or stored the drive in a humid environment like a basement or garage. Some drives started exhibiting these symptoms after a few years. Today this problem is very common. Don’t buy a dark beige 1541 drive with a lever that turns without confirming it works. A 1541 with an oxidized head won’t read the disk, and no amount of cleaning or aligning the drive helps.

In 1986, Commodore replaced the 1541 with the 1541C, which matched the lighter beige color of the Commodore 64C and 128. And then in 1988, Commodore released the 1541-II, which was also light beige, but it was smaller and ran cooler because it had an external power supply, and more importantly, it had DIP switches so you could have multi-drive setups with less effort.

The model 1541 is the most common of Commodore disk drives, and none of the 1541 variants are especially rare.

The Commodore 1541’s popularity

Disk drives were uncommon in Europe, but that wasn’t the situation in the United States in the 1980s at all. Cartridge-based software fell out of fashion around 1984, and tapes were never common here. I knew exactly two people who ever bought a Commodore 64 and didn’t get a disk drive.

When the 1541 first came out in 1982, Commodore charged $299 for it. That meant you could get a Commodore 64 and a disk drive for less money than a competing computer alone. Commodore didn’t cut the price on the 1541 nearly as fast as it cut the price on the 64, but they didn’t have to. Commodore couldn’t keep up with demand for the 1541 even as late as spring 1984. In 1983, Commodore reported that 90 percent of Commodore 64 buyers in the United States bought 1541s. Commodore expected an adoption rate of 30 percent.

Using the 1541 with the VIC-20

If you used the 1541 with the VIC-20, you could send a command to the drive to change its timing to match the 1540 and speed it up about 10 percent.

OPEN 1,8,15,”UI-“:CLOSE 1

Why the Commodore 1541 was so bulky

The 1541 was bigger and bulkier than the drives for many other computers, partly because it was more than a disk drive. Commodore disk drives were “intelligent” peripherals, meaning they had their own CPU, memory, and I/O chips inside. They were a simple computer unto themselves. This meant that Commodore’s disk operating system didn’t take up any memory inside the computer itself, which left more memory available for programs. But it also meant the drive had to be wider and deeper than, say, an Apple drive, because Commodore had to leave room for all those chips inside. Apple drives were just a drive mechanism in a metal case with a ribbon cable that connected to the computer, so they looked a bit sleeker.

To some extent this led to problems late in the Commodore 64’s life, since it was nearly impossible for Commodore to get the cost of the 1541 much below $150. Had Commodore been able to lower the price further, multi-drive C-64 setups might have been more common, and more complex software taking advantage of those multi-drive setups might have appeared.

Changing the device number for multi-drive Commodore 64 setups

Commodore 8-bit computers addressed devices on its serial bus by numbers. The default disk drive was device 8. You could add additional drives on higher numbers. A second drive was device 9, a third drive was device 10, and so on. Prior to 1987, 1541 drives shipped from the factory hard-wired as device 8, and to change it, you had to open the drive and cut jumper pads on the drive’s printed circuit board. This wasn’t something many people were willing to do on a newly purchased piece of equipment that cost $200, especially since it voided the warranty.

I think this was a favor to Commodore dealers. An experienced technician could make the modification in a few minutes. I’m sure the dealer next to me charged you for the modification even if you bought the drive from them, but a smart dealer would do it for free so you’d buy the drive from them instead of from Toys R Us or Kmart or Target.

The cheater’s way to change a 1541 device number

The usual way is to cut the jumper pad, but there’s another way. You can remove VIA-1 (one of the two 6522 ICs) and bend pin 15 ninety degrees then put it back in the socket. This changes the drive from 8 to 9. For device 10, bend pin 16 instead. For device 11, bend both 15 and 16.

How to tell which chip? Position the board so the two diamond-shaped heat sinks are in the upper left corner.

If you have a long board, the VIA-1 (UAB1) is near the bottom edge, about a third of the way from the left. Count from left to right along the bottom side of the IC (1 to 20) to find pin 15.

If you have a short board, four chips are stacked vertically near the center. The one you want, UC3, is the third from the bottom. Count from left to right along the bottom side of the IC to find pin 15.

Changing a device number through software

You could also change a device number through software. Simply power on one drive, then issue the command, then power up the second drive:

OPEN 1,8,15,”M-W”;CHR$(119);CHR$(0);CHR$(2);CHR$(9+32)+CHR$(9+64):CLOSE 1

To use a different device number, change the number in bold. The command was cryptic but doable. Many disk copy programs included functionality to change a device number for you.

Buying a Commodore 1541 disk drive today

If you go to buy a Commodore 1541 disk drive today, I don’t recommend buying an untested one. The drives with the older flip-down latch indicative of an Alps mechanism are fixable. If you get a drive with a Mitsumi or Neutronics mechanism and it has an oxidized head, you have to replace the head to fix it.

A 1541-ii drive is a better bet. The drive mechanisms in those are more reliable, and by the time the 1541-ii was released, Commodore had six years to work out the frailties of the 1541. A 1541-ii may also be cheaper to ship.

Emulating the 1541

Today, many people, rather than using a real 1541, will use an emulator that allows them to load a disk image, or lots of disk images, onto an SD card. This is faster, more convenient, and more reliable than relying on disks.

2 thoughts on “Commodore 1541 disk drive

  • September 30, 2018 at 1:24 pm
    Permalink

    Very interesting and informative! I really enjoy reading about other Commodore user’s memories and experiences of computing on our C64 and C128, “back in the day.” Fantastic!
    David.

    Reply
    • September 30, 2018 at 1:34 pm
      Permalink

      Thanks! Revisiting those old memories can be a lot of fun. And I suppose it can be a bit humorous. My kids are both just past the age I was when I got a 64 and 1541 growing up. They have laptops I rebuilt for them and outfitted with SSDs. I had that loud, lumbering 1541.

      Reply

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