Commodore 1571 disk drive

Last Updated on July 15, 2021 by Dave Farquhar

The Commodore 1571 was Commodore’s successor to the notorious 1541 disk drive. It addressed many of the shortcomings of the 1541, partly because Commodore had more time to get it right this time. It was the same color and style as the C-128. And they worked as well together as they looked together. It was a high-end drive, but I hesitate to call it Commodore’s top-end 5.25-inch drive. I’d give that distinction to the SFD-1001.

Commodore introduced the 1571 in 1985 at a price of $299 US. It was a double-sided, double density 5.25-inch disk drive that was faster than the 1541 when you used it with the 128, and maintained good backward compatibility with the 1541 when needed.

Quieter. Faster. Better.

The 1571 incorporated a better drive mechanism that had a head sensor in it so the drive didn’t knock nearly as much as the 1541 did. While the drive still wasn’t silent, it was far quieter than the 1541, which was so loud it’s the main thing people who owned one remembers about it.

Commodore intended for the 1541 to be reasonably fast, but a bug on the C-64’s circuit board put an end to that. The flaw was correctable but that would have delayed its release. The 1541 transferred data at a rate of about 300 bytes per second. The C-128 and 1571 combination were about 9 times as fast, which was much more competitive with other computers of its day. It wasn’t quite as fast as the 1581, but that’s due to the 1581’s better seek times.

Overall it was a better and more capable drive than its predecessor. It ran cooler than the 1541. Some sources express curiosity at this, as it still has an internal power supply like the 1541 did, but it used lower power chips like the 65C22 and a more modern, cooler running power supply. That combination helped keep it cooler. It also had DIP switches on the back to change the device number, so you didn’t have to open the drive and cut traces to use multiple drives.

Commodore had trouble getting enough drive mechanisms, so the 1571 was in short supply for its first year or so on the market. Commodore tried to alleviate this by releasing the 1570 drive in Europe, which also helped soak up an excess of 1541 parts.

A smart peripheral

Like the 1541 and every other Commodore IEC bus peripheral, the 1571 was a computer unto itself. It had a 6502 processor, a complement of I/O chips, and its own RAM and ROM.

Commodore never quite got the 1571 ROM right. The first ROM had a bug in handling REL files. The second revision decreased its 1541 compatibility. When I upgraded the ROM in my 1571, I bought a JiffyDOS ROM, which incorporated the best code from both ROM versions. Commodore called the 1571 ROM version 3.0, and the ROM in the 1571 built into the C-128D version 3.1. The 1541’s ROM was version 2.6.

I don’t know how many people bought JiffyDOS to get the bug fixes, but it was worth it just for that. At least I thought so.

The 1571’s enhanced capabilities

Unlike the 1541, the 1571 could read and write MFM-formatted disks in addition to GCR, thanks to Commodore including a WD1770 disk controller. Yes, WD stood for Western Digital–that Western Digital. Commodore intended this for reading CP/M disks from systems like Kaypro and Osborne, but it wasn’t long before someone wrote software to read and write MS-DOS disks as well. The 1571 stored about 340K in its native format, with 1328 blocks free according to Commodore DOS, and 144 directory entries. There was a trick to free up track 36 on the flip side to get a few extra blocks free.

With custom MFM disk formats it was possible to store 400K on a disk. Using them required hacking the CP/M boot disk and entering parameters manually, but I thought it was worth it to get almost 20% more storage on a disk. Reading those disks today would give me a problem if I ever find them again though, unless I also find my custom CP/M disk.

I knew people who had 1571s who never realized the drive would use both sides of the disk. They thought it was weird I didn’t notch my disks and flip them. I don’t know how widespread that was, but at least some 1571 owners, including members of my local users group, didn’t use them to their fullest capability.

Backward compatibility with other computers

The 1571 worked with any Commodore 8-bit computer with a Commodore IEC port. That meant the VIC-20, C-64, Plus/4, 16, 116, or 128. With any machine other than the 128, it would default to its 1541 emulation mode. You could easily change modes with these commands:

OPEN1,8,15,”U0>M1″ : REM 1571 MODE

OPEN1,8,15,”U0>M0″ : REM 1541 MODE

In 1541 mode, it just used one side of the disk, and ran at exactly the same speed as a 1541.

In 1571 mode, it still ran at 1541 speeds with earlier computers and you lost some compatibility but you could use both sides of the disk. The compatibility issues were generally only a problem if you had a fast loader or were using copy protected software. Later fast loaders supported the 1571 in native mode on the 64.

The 1571’s backward compatibility with the 1541

The Commodore 1571 was mostly compatible with the 1541, but Commodore knew it couldn’t make it 100%, so it never advertised it as such. In practice, it was close enough. A few Microprose and Accolade titles reportedly caused trouble, but not all. I had plenty of titles from both publishers that worked, and I’ve never seen the list of titles that didn’t work.

If a game you really wanted was among the ones that didn’t work, I can imagine being sour on the 1571. But Commodore sold enough 1571s that I can’t imagine those titles didn’t get fixed to make them compatible. Accolade was one of my favorite publishers and I never had a problem getting any of their titles to load.

Changing the 1571’s device number in hardware

To change the 1571’s device number in hardware, use the DIP switches in the back. They are exactly the same as the later 1541-II. This was an intentional decision on Commodore’s part.

The ability to change the device number in hardware makes the 1571 popular with retro computing enthusiasts. I’ve even seen people use multiple 1571s with C-64s, even though dual 1541 setups were much more common with that machine. The 1571 is the more capable drive.

The Commodore 128D

Commodore sold a version of the 128, the 128D, that included a 1571-compatible drive in an enclosure that somewhat resembles an Amiga 1000. The drive in the initial 128 was completely compatible with the separate-sale 1571. The drive in the later cost reduced version wasn’t quite 100% compatible due to some changes in the design.

There was no way to turn off the 128D’s built in drive without installing a switch yourself, but there was a workaround if you didn’t want to modify the machine. You could change the drive’s device number to something out of the way, then power up an external 1541 or 1571 that you wanted to use as drive 8.

The command to change the device number was as follows:

OPEN 1,8,15,”U0>”+CHR$(13):CLOSE 1

Substitute any number up to 35 for 13.

Popularity

The 1571 sold well to 128 owners, but some number of people who upgraded from a C-64 opted to continue using a 1541. The 1541 was completely compatible with the 128, it was just slower. And aside from a few Infocom titles, nothing for the 128 required the 1571. GEOS took advantage of the 1571, but didn’t require it. The 1541 was the lowest common denominator, so most 128 software assumed a 1541.  The 1541 went on sale much more often than the 1571, so unless you knew about the 1571’s advantages, the 1541 was a tempting choice. Commodore didn’t do a good job of talking up the drive.

The 1571 is popular today, because it was a good drive. It’s rarer and more expensive than the 1541 for that reason.

Taking care of your 1571

If you have a 1571, it’s prone to one mechanical problem with the drive heads. The spring can get weak over time, preventing the drive from engaging. You should store a 1571 with the head protection card in the drive and the drive closed, or if you don’t have one, with a disk in the drive. Put the disk in rotated 90 degrees to avoid having magnetic particles from the disk get stuck on the drive. It looks weird, but it will help keep your drive in working order for years to come. Parts are difficult to come by these days, so it’s worth doing.

1571 or 157I?

Almost every time I bring up a Commodore disk drive on a discussion board, someone brings up the proper name, noting the nameplate substitutes the letter “I” for the second 1.

This was acceptable typography for much of the 20th century. For that matter, some manual typewriters didn’t even have a 1 key, so you had to use the letter I to type a 1. The first typewriter I learned to type on was like that. No, I’m not that old, the school I attended was behind the times.

Someone decided that a European-style 1 in the front of the number and an I at the back looked good. It did let them space the numbers a bit more consistently. It looked a little old-fashioned too, but the C-64’s color scheme was also old fashioned. All of it went together. The old-style number for the 1571 didn’t fit quite as neatly into the 128/1571 motif, but it at least let them make the badge smaller.

This type of design was out of fashion by the time I was taking design classes in the 1990s, but I do remember an instructor mentioning it was something you could do if you wanted to invoke age.

No one thought any of this was odd in the 80s. Everyone I knew read it as “1571,” not “fifteen-seventy-eye.” Commodore’s sales literature all referred to it as the 1571, as did the cover of the manual, and so did all the books and magazines of the time. And the 1571’s FCC ID was BR97TB1571. The applicant picks the last seven characters. Commodore could have chosen 7TB157I, but they didn’t.