IIRC, this isn’t quite accurate.
Lexmark initiated a lawsuit against a third party company that was selling chips to companies that made replacement toner cartridges for laser printers. The chips contained a small program, known as the Toner Loading Program, which measured the amount of toner left in the cartridge. The printer itself contained another program (the Printer Engine Program, I think) that performed the actual printing, and it would check that the TLP code in the toner cartridge exactly matched Lexmark’s code before it would allow any printing. Lexmark lost, so the other company is allowed to keep making replacement chips.
Lexmark’s claims were something like this:
[li]By copying the TLP code verbatim, the company had allegedly infringed Lexmark’s copyright on the program. The court found that the program was uncopyrightable because it was purely functional - there was literally no reasonable way to implement the program differently, partly because it was so limited in scope that there was no room for creativity (the code is just a simple equation to calculate the amount of toner from a wheel’s rotational speed), but mainly because it acted as an access key, so that the only possible way to make a working TLP was to copy Lexmark’s code.[/li][li]By gaining access to the PEP without Lexmark’s permission, the company had allegedly helped users circumvent an access control on the PEP, which would be a DMCA violation. The court found that buying the printer is what gives the user access to the PEP, since the program is stored unencrypted and can be read off the printer chips using common electronics tools - “access” doesn’t just mean the ability to run the program.[/li][/ol]
Yes, yes, a thousand times yes. A printer manufacturer has no more right to tell you what cartridges you can put in your printer than a car manufacturer has to tell you where you can buy gas for it. If they wanted to maintain control over it, they shouldn’t have sold it to you in the first place; once you buy it, it’s yours, and you can fill it with pudding and coffee if that’s what you want.