Last Updated on December 7, 2023 by Dave Farquhar
The Commodore SFD-1001 is a somewhat obscure Commodore disk drive that found itself in an odd spot. It was a nearly state of the art drive when Commodore released it in 1984, but it worked with a computer line that Commodore wasn’t making anymore. It gained a cult following regardless, and retains a fair bit of mystique, and collector interest, to this day.
What the SFD-1001 was
The SFD-1001 was a quad density 5.25-inch disk drive that used Commodore’s IEEE-488 bus. It was a single-drive version of Commodore’s earlier 8250LP disk drive, built into a 1541-like case. It looks like a 1541 with a different drive mechanism in it. A Panasonic JU-570 or JU-570-2 in this instance. And it was a behemoth. It stored a megabyte on a single 5.25 inch disk.
Sounds a little like the 1.2 megabyte high density drives in the IBM PC/AT, doesn’t it?
It’s a similar drive capacity-wise. But it uses a different type of disk. The SFD-1001 won’t work with PC high density disks. Quad density disks are hard to find, and they were even hard to find in the 80s. It turned out that you could format regular double density disks (the same disks used in the 1541) as quad density disks and they usually worked. No disk manufacturer would guarantee them if you did that, of course. But with no other options, people did it. And even Commodore recommended using high-quality double-density disks with the drive in the service manual for it.
Quad density disks and drives are unusual, and not a lot of computer makers used them. Digital Equipment Corporation used them in its DEC Rainbow 100 that ran CP/M and MS-DOS. Leave it to Commodore and DEC to find an oddball format and use it. Tandy also used it in its ill-fated Tandy 2000 PC from 1983.
The SFD-1001 is completely compatible with the earlier 8250 dual drive, and can read and write the single-sided quad density disks from the 8050 dual drive. But it cannot read a 1541 disk, or disks from any of the PET line’s double density drives, like the 2040, 4040, and 2031. Commodore had a lot of redheaded stepchildren, and the SFD is one of the best examples I can think of.
The SFD-1001 vs other Commodore disk drives
The SFD-1001 looks like a 1541 at first glance, but it’s incompatible with it. It uses the same DOS 2.7 as the 8050 and 8250 dual drives, and like those drives, it has two CPUs. Two full-blown 6502s in this case, rather than pairing up a 6502 with a cut-down model like a 6504. One CPU performs file handling and data transfer and one handles the disk controller.
Since it’s a two-sided drive, it has two drive heads. It does use GCR like other Commodore drives, and it has a variable number of sectors per track. It has 77 tracks, 23-29 sectors per track, shows 4,133 blocks free when you run a directory on a blank disk, and can store up to 224 directory entries. The actual storage capacity was 1,066,496 bytes per disk, just a shade over a megabyte.
Because of the vast differences between the SFD-1001 and the 1541, it’s not compatible with it. Software that uses the standard Commodore Kernal routines for file handling will work fine with the SFD, but anything that sends code to the drive to run internally is likely to fail, because the SFD’s internals are so different.
There’s one more feature the SFD-1001 has that Commodore’s other drives, at least their consumer-oriented drives, lacked. A 1541, 1571 or 1581 can have one of four device numbers set via hardware. Connecting more than four is possible, but requires setting a device number in software with one drive powered on at a time. The SFD-1001 can have one of eight device numbers in hardware. So you can easily set up an 8-drive system, as long as at least four of them are SFDs. One BBS operator I knew had at least six drives connected and I always wondered how he did it. Two of his drives were SFDs, so now I know.
Who liked the SFD-1001
The SFD-1001 gained a cult following, especially among BBS operators. The SFD-1001 was robust and proven, being derived from the earlier 8250 drive. Its DOS was less buggy than the 1581, which had a tendency to mix data files, and its handling of REL files for databases was unreliable. It stored 25% more data than a 1581, and it used cheap 5.25-inch disks, which you could buy in quantity for 19 cents apiece in the late 1980s. And since it used the IEEE-488 bus, it was fast. I knew three BBS operators in St. Louis who had them, and they loved them. Putting your user database or a message board on a 1581 was risky, but you could do both on an SFD. You didn’t have to relegate it to file transfer duties.
Of course, there were downsides. You could get a 1581 much more easily in the late 1980s. All the mail-order dealers had them in stock. SFDs were scarce. To use one with a C-64 or 128, you had to buy a separate IEEE-488 interface, which occupied your cartridge port. The interface cost $70 and the cable cost another $30.
If you wanted to use something else with it, you had to get a cartridge port expander. But even then, you had limitations. You couldn’t use a fastloader with a 1541 in conjunction with the SFD.
But the SFD owners I knew loved the upside. And they were pretty outspoken about how great their drives were. Being able to connect up to 8 drives as long as four of them were SFDs made it even better.
Getting an SFD-1001
Commodore introduced the SFD-1001 in 1984 or possibly late 1983 and discontinued it in 1985. As far as I know, in the United States, Commodore never sold it through its regular dealer network.
The story I heard was that Commodore farmed out distribution to Progressive Peripherals and Software, a company that produced software and peripherals for Commodore computers. Commodore and Progressive had a somewhat unique relationship, in that Progressive licensed some software to Commodore to distribute under the Commodore name.
But still, it’s odd that Commodore would produce a new product, then immediately turn the inventory over to another hardware manufacturer to distribute it.
The retail price on the SFD was $399, though by some accounts Progressive sold the drive for closer to $300 at least sometimes. Progressive rarely advertised it, which makes it hard to know when they ran out of inventory. The SFD owners I knew loved to talk about their drives, but I never had any reason to ask where they got them.
Protecto Enterprizes, a large Commodore mail order house near Chicago, had a limited inventory of the drives. They sold them in the summer of 1985 for $180. They never mentioned the name or model number, but no other drive on the market besides the SFD matches Protecto’s description. It’s possible that part of the deal was that Progressive could use the name but Protecto could not.
Why Commodore built the SFD-1001
Why Commodore bothered to build the SFD-1001 seems like a totally fair question. And I can’t find a good answer for that. Commodore didn’t really intend to be finished with the PET line in 1982. They developed a sleek product line to replace the PET in the early 1980s, but due to the success of the C-64, few of them were produced and those that did ended up at liquidators. Commodore didn’t have the capacity to build both.
Commodore discontinued those machines in 1984. That was the same year Commodore introduced the SFD-1001. Maybe Commodore put the SFD into production before its CBM-II line went by the wayside. But since the Commodore magazines of the time were all focused on the 64, none of them mentioned any of that, so it’s hard to know.
It’s also possible Commodore had the quad-density drive mechanisms sitting in inventory, and decided the fastest way to get rid of them was to build a single-drive version of the 8250 and then hand them off to someone else. That sounds like a very Commodorey thing to do.
The SFD-1001 today
Commodore collectors covet the SFD-1001. As I was researching this, I saw two for sale for over $500. None had sold for that price in the last 90 days, which suggests that price is too high. But I have seen a broken SFD sell for nearly $200. SFD-1001s are rare, and whether they work or not, they’re valuable.
The JU-570 mechanism is prone to leaky electrolytic capacitors. There’s no guarantee that if you find a broken SFD-1001 that’s all that’s wrong with it, but recapping the drive mechanism is something you’ll want to do, at least as preventative maintenance. The drive doesn’t fail immediately after capacitors start to leak, so a drive that does work can have leaky caps.
David Farquhar is a computer security professional, entrepreneur, and author. He started his career as a part-time computer technician in 1994, worked his way up to system administrator by 1997, and has specialized in vulnerability management since 2013. He invests in real estate on the side and his hobbies include O gauge trains, baseball cards, and retro computers and video games. A University of Missouri graduate, he holds CISSP and Security+ certifications. He lives in St. Louis with his family.