It's actually a great example of a user-unfriendly UI. Most people still don't know what it means. PC does not stand for Personal Computer.
The error message comprises three parts. "PC" is an abbreviation for "paper cassette", the tray which holds blank paper for the printer to use. These two-character codes are a legacy feature carried over from the first LaserJet printers, which could only use a two-character display for all printer status and error messages. "Load", in this context, is an instruction to refill the paper tray. "Letter" is the standard paper size (8.5 × 11 in.) used in the United States and Canada. Thus, the error is instructing the user to refill the paper tray with letter-sized paper. Variants are "PC LOAD LEGAL", meaning that the printer needs more legal size (8.5 × 14 in.) paper, and "MP LOAD [paper size]" meaning the printer needs paper in the "MP" (multi-purpose) tray, and "[paper size]" is the name of the size of paper specified for the print job.
We discovered these displays could be updated via a curl command at one of my previous jobs and they quickly started saying things like "FEED ME KITTENS".
I had a boss that absolutely freaked out when he saw that the printer was set to scroll “SELF DESTRUCT IN”, “3...”, “2...”, “1...”, “MAYBE NEXT TIME!” every few minutes. I had a cron job set up to run a Python script every minute with a 1:10 chance of displaying it.
He stood there watching it for probably an hour, before running to his office and making a panicked call to PC Services about how our network had been hacked.
I messaged a friend in that department and owned up to it. He later told me he logged an hour “solving” that problem and requested a copy of my script.
Turns out that in the year 2018/2019, if you leave printers connected directly to the Internet, which will print any jobs sent to them, you get this as a result:
The error message comprises three parts. "PC" is an abbreviation for "paper cassette", the tray which holds blank paper for the printer to use. These two-character codes are a legacy feature carried over from the first LaserJet printers, which could only use a two-character display for all printer status and error messages. "Load", in this context, is an instruction to refill the paper tray. "Letter" is the standard paper size (8.5 × 11 in.) used in the United States and Canada. Thus, the error is instructing the user to refill the paper tray with letter-sized paper. Variants are "PC LOAD LEGAL", meaning that the printer needs more legal size (8.5 × 14 in.) paper, and "MP LOAD [paper size]" meaning the printer needs paper in the "MP" (multi-purpose) tray, and "[paper size]" is the name of the size of paper specified for the print job.