The dark tan 1541 is the most common C-64 peripheral in existence. Its counterpart for the VIC-20, which looks exactly like it at first glance, is pretty rare. The 1540 vs 1541 is a fairly common topic among Commodore enthusiasts.
Commodore 1540 disk drive
Internally, the difference between the Commodore 1540 and 1541 is a ROM chip marked 325303-01. There are three options to turn it into a 1541. You can replace the 325303-01 with a 901229-01 or 901229-03. Or you can install a 1541 JiffyDOS ROM. Converting a 1540 to a 1541 makes it much more useful, since a 1541 works with newer Commodore computers. Because of this, most 1540s received this modification at some point, making an unmodified 1540 a collector’s item.
That ROM and the badges on the front and back are the only difference between a 1540 and an early 1541. The drives even have the same FCC ID.
Why the difference?
The design of the VIC-20 allowed the disk drive to transfer at a higher rate. The 64’s bigger screen changed the CPU’s timing, and Commodore had to tweak the ROM to slow down the 1540 a bit to make it work. The revised drive became known as the 1541.
Very early 1541s are the same color as the 1540. That is, they’re the same color as the VIC-20. The sticker on the back even says VIC-1540 on it, although the badge on the front says VIC-1541 or 1541. These early 1541s are less common than the dark beige 64-colored 1541s, but nowhere near as rare as a true-blue 1540. Commodore dropped the VIC nomenclature in 1983 because it didn’t want to suggest the 1541 was somehow incompatible with the 64.
Why the 1540 is faster than the 1541
The 1540 is slow because of a bug in the 6522 VIA chip. Initially, Commodore intended the 64 and 1541’s speed to be comparable to that of the 128 and 1571. A bug in the 64’s motherboard design made that impossible. Furthermore, the screen size of the 64 changed the CPU’s timing, so Commodore had to slow the disk drive down a bit more to work around the timing issue. Had the bug in the 64’s motherboard not been there, the workaround for the 64’s screen wouldn’t have been noticeable. Having to run the 1541 at an even slower speed than the already-slow 1540 just added insult to injury.
I get tons of comments saying the screen size can’t possibly have anything to do with it, but in the 64, everything was connected. You can make the 1540 work with the 64 if you blank the screen.
Numerous companies devised ways to speed up the 1541 later on, which led to the cottage industry of fast load cartridges. But in 1982, Commodore had a deadline to meet. Some fastloaders blank the screen so they can switch back to the 1540’s timing for a very slight speed increase.
Testing a 1540 vs 1541 upgraded 1540
If you want to test a 1540 to see if it’s been upgraded without opening it, up, try it out with a 64. If you need help hooking up the drive, here’s how. Insert a known working disk and see if the drive is able to load it. If you don’t have a disk to use, you can try formatting a blank disk and save a simple program to it.
Format a disk:
OPEN 1,8,15,"N0:DISK,I00":CLOSE 1
Type in a program:
10 PRINT "HELLO, WORLD!"
See if it worked. An unmodified 1540 won’t get this far. Test by re-loading the program:
If all that works, the 1540 was modified. If it doesn’t work, you’ll want to investigate further by trying it with a VIC-20, but don’t make any changes to it because it’s more collectible unmodified. Like the silver-label 64, the rarer, less useful state is more valuable. It’s better to leave it alone and use one of the common variants. A working garden-variety 1541 probably costs less than the upgrade, and a 1541-II is a better drive all around. Commodore figured a few things out over the course of a decade, and the 1541-II incorporated those lessons learned.
Even if your 1540 has a replacement ROM chip, the less you modify it, the better off you’ll be. If you’re looking to soup up a 1541, soup up the common variant. The closer a 1540 is to pristine, the more valuable it will be. That’s partially because way back when, a 1540 was a dog, so when someone had both a 1540 and a 1541, it was the 1540 that would get the 8/9 switch and other modifications. Commodore’s later drives were usually better than the earlier ones, so the newer drives were more likely to act as the primary drive and stay unmodified.
1540 vs 1541 value
When I see a 1540, it typically sells for 4-10 times as much as a common 1541. In 2016 I saw bare 1540s of questionable heritage sell for $60. On the other extreme, I saw a pair of boxed 1540s sell for $185 and $305, respectively. Both had original ROMs, but the cheaper 1540 had a reset switch. The costlier 1540 was wired to device 9 but otherwise appeared unmodified, so it commanded a significant premium. Prices have gone up over time. In 2020, I saw a bare 1540 sell for $289.
As for the 1541, its value has also increased, but not as dramatically. A tested, working 1541 sells for $50-$80 in 2020.
Should you use a 1540?
If you have a VIC-20, there’s no reason not to use a 1540, but an early 1541 in a VIC-colored case is cheaper and easier to get. Installing JiffyDOS in both the VIC and your VIC-1541(s) makes them much more pleasant to use.