Later revisions of the Commodore 2031 look just like the 1541. But was this drive just the IEEE version of the 1541? And what about this drive almost made the 1541 not happen at all? In this blog post, we will dig into the last 170k IEEE drive Commodore made for the PET series, from 1981 to 1983.
The first 2031
Early 2031 drives don’t look anything like a 1541. They look like a 9060 or 9090 hard drive with the Shugart SA-400 drive mechanism from a 4040 in it. Or I guess you could say they resemble half of a 4040, without the angled styling.
Inside, it’s not exactly half a 4040. The 2031 motherboard resembles the 1541 more than it resembles the 4040. Unlike the earlier dual drives, it only has a single 6502 CPU. And it also runs Commodore DOS 2.6, like the 1541. This means its disks are fully compatible with the 1541, and suffer the same incompatibility is with the 4040 that the 1541 does. The two drives read each other’s disks just fine, but due to a difference in their header byte, the two drives cannot reliably write to disks written by the other type.
The similarities with the 1541 are more than superficial. According to internal Commodore memos that Michael Tomczyk provided to Dave McMurtrie’s Commodore International Historical Society, Commodore considered releasing the 2031 with both a VIC-compatible IEC interface and a PET-compatible IEEE interface, like an MSD Super Drive. They decided against it partly because they wanted the flexibility to charge different prices for the PET and VIC versions of the drive. Also, including both interfaces would have increased the cost of the drive, and Commodore wanted VIC-20 peripherals to cost as little as possible.
This early version of the 2031 in a metal case reached the market in 1981.
Second generation 2031
The second generation 2031 was a cost reduced version that used a half height drive mechanism and a VIC-1540/1541 case. The color of the case matches the VIC-20 exactly, which also means it’s not a bad match for a PET. A major difference between the cases is that the opening where IEC connectors would go is enlarged slightly to accommodate an IEEE-488 connector instead.
I’ve heard people call this drive lower quality, but that seems a little harsh. Yes, the rugged metal case got replaced with a plastic case, so the drive doesn’t cool as well, but the electronics inside are still the same. The drive mechanism is different, but is the half height Alps mechanism really any inherently lower quality than the full height Shugart SA-400 mechanism? The major problem with the Alps mechanism was that it would go out of alignment from banging its head due to copy protection scheme. On the PET, that wasn’t really an issue. On the other hand, the Shugart could only reliably go out to track 35, where the Alps mechanism could easily read and write 40 tracks. The limitation of 35 tracks in Commodore DOS is an artifact of the Shugart drive.
A second-generation Commodore 2031 disk drive looks like an early VIC 1540 or 1541 drive from 1982, right down to the silver labels. I’ve heard claims that it is the rarest Commodore floppy drive, but I see more of them than I see a 1540 or SFD-1001 drive. I agree this drive is rare, but I’m not sure I would give it the title of rarest.
Commodore 2031 LP
The 2031 LP was the last version of the 2031. Both of the 1541-style 2031s were low profile drives, but this later version included those letters in the model number.
This drive has the rainbow label, embossed Commodore logo on the top, and VIC-20 coloration like the later model VIC-1541. This drive remained available until late 1983.
It’s also an open question which of the 1541-style variants is rarer, but I’d lean toward the 2031LP due to Commodore’s supply chain issues in 1983.
Differences with the 1541
Even though the later revisions look like a 1541, all models of the 2031 are much faster than a 1541 because they use the IEEE bus. You can connect one to a C-64 or 128 with an IEEE cartridge, but it will have compatibility issues with software that includes a 1541 fast loader. It’s really better suited for use with a PET.
Commodore released this drive late in the life of the PET series, and the later versions are similar enough to the 1541 that Commodore could produce them more cheaply than the earlier IEEE drives. But Commodore had difficulty keeping up with demand for the 1541, so when push came to shove, if there was unmet demand in the sales channel for the 1541, Commodore was making 1541s, not 2031s.
It is possible to change some circuitry and patch the ROM in a 1541 to turn it into a 2031 workalike. Some PET owners in Europe resorted to this in the 1980s. The German magazine 64er published plans for doing this around 1985. That proved timely, given that MSD discontinued its dual IEEE/IEC drive right around that time. A modern reimplementation called the Nu2031 is available on Github.
David Farquhar is a computer security professional, entrepreneur, and author. He has written professionally about computers since 1991, so he was writing about retro computers when they were still new. He has been working in IT professionally since 1994 and has specialized in vulnerability management since 2013. He holds Security+ and CISSP certifications. Today he blogs five times a week, mostly about retro computers and retro gaming covering the time period from 1975 to 2000.