Commodore hardware viruses–yes, they were possible

The conventional wisdom is that computer viruses can wipe out your data, but they can’t do physical damage. The exception to that rule was, of course, Commodore, the king of cheap 1980s computers. Commodore’s earliest computer, the PET, had an infamous “poke of death” (POKE 59458,62) that would destroy its video display, but the Commodore 64’s sidekick, the 1541 disk drive, had a couple of little-known vulnerabilities as well.

Commodore hardware viruses
Typing POKE 59458,62 into a Commodore PET would permanently damage its display circuitry.

A St. Louis-area software cracker who went by the handle of Iron Doctor (if I ever knew his real name, I forgot it long ago) told me about these many, many years ago. I didn’t want any part of the software cracking scene but the budding journalist in me was utterly fascinated by it, so I talked to software crackers a lot, while resisting the repeated invitations to join their groups.

Commodore copy protection (some would argue it’s more properly called “copy prevention” or DRM) schemes tended to be very elaborate. The 1541 was a computer in its own right, with a 1 MHz 6502 CPU and 2 KB of RAM, so clever programmers had a lot of options with it.

Iron Doctor told me that he’d seen protection schemes that, if they detected you had tampered with them, would try to break your disk drive in retaliation. The most common way to do this was to send the drive a command to try to move the drive’s stepper motor beyond its physical range. The drive would oblige and try to do the impossible, so it was possible to command the drive to permanently damage its own drive mechanism.

But the 1541 had another issue. Although it’s impossible to write to ROM, Commodore left out the circuitry in the 1541 that would keep its CPU from trying to do so. Commodore was trying to meet a price point with the 1541, and who would ever try to make the disk drive write to ROM, anyway? So it’s understandable why they would leave out that logic and save a buck. But if your program tried to write to ROM and did it often enough, you stressed both the CPU and ROM chip and could cause one or the other to overheat and fail.

While this isn’t a virus in the strictest definition of the word, it’s certainly malicious, and fixing it would have been a $75-$125 repair, depending on how quickly the technician could diagnose the problem. Some repair shops were much better than others.

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