What is the Terry Pratchett's out of cheese joke about?

Reading Terry Pratchett's books, and the machine Hex sometimes says

Out of Cheese Error. Redo From Start

What is the joke referencing?

It reminds me of my early days when I learned BASIC or QBASIC or maybe DOS.  I miss DOS.

But I cannot remember what it refers to and it bugs me.

There's also a time when HEX goes on about melons which I think I should know this joke too.  But I cannot remember.

I've never read the books, but you got me curious. I found this quote online http://chris-miller.org/out-of-cheese/

Anyway on first hearing this I thought that I had heard it somewhere before however couldn't remember where. After forgetting all about this I was sitting in bed a few nights ago reading Interesting Times by Terry Pratchett. This book contains a machine called Hex which was made by a wizard, basically it's the first computer ever on the Discworld, it works by having thousands of ants running through tubes, controlled by leavers and a huge keyboard. It tends to add things onto itself and grows larger and more complex on its own. A mouse had made its nest in the middle of the machine and when it was removed it made the whole thing not work, therefore it was left and allowed to live there.

An extract of the book is given below, a wizard named Ponder Stibons has just used the machine to generate a spell and had said Thank you to it:

He was beginning to suspect that Hex was redesigning itself. And he'd just said 'Thank you'. To a thing that looked like it had been made by a glassblower with hiccups. He looked at spell it had produced, hastily wrote it down and hurried out. Hex clicked to itself in the now empty room. The thing that went 'parp' went parp. The Unreal Time Clock ticked sideways. There was a rattle in the output slot. 'Don't mention it. ++???++ Out of Cheese Error. Redo From Start.'

It looks like the computer had a mouse take residence, and somehow this mice became essential to the HEX machine working. If the mouse was removed, the machine didn't work. And, if there was no cheese, the mouse might/could leave, making the machine unable to work. So, to keep itself going, it required cheese, and would make error messages when more cheese was needed,

At least, that's what I'm getting out of the above quote. No idea why the out-of-cheese message came a that point. Maybe because the machine was learning to care for others, and it started by caring for the mouse it needed to function??

From Discworld Wiki https://en.wikipedia.org/wiki/Hex_(Discworld)

It alludes to the many confusing error messages that technology users have had to put up with in the Information Age. "Out of Paper" (also seen as "PC LOAD LETTER" for some printers) is familiar to many office workers. "Redo From Start" was the somewhat unhelpful error message produced by the BASIC interpreter in many early home computers when non-numeric characters were entered in response to a prompt for numerical input. Other inscrutable Hex-talk includes:

+++Mr. Jelly! Mr. Jelly!+++
+++Error At Address: 14, Treacle Mine Road, Ankh-Morpork+++
+++MELON MELON MELON+++
+++Divide By Cucumber Error. Please Reinstall Universe And Reboot +++
+++Whoops! Here Comes The Cheese! +++
+++Oneoneoneoneoneoneone+++

So, it looks like the "redo from start" was for when someone gave an order in the wrong way. And, the melon, cucumber, etc jokes were to poke fun at how unintelligible some error messages are?

Maybe cheese is in some way essential to memory?  

So instead of an 'out of memory' error you get an 'out of cheese error'. Which means you need to stop farting about with the computer and go get something to eat.

Which, from what I know about bearded, hiking-boot clad programmers, would probably mean part of the remaining lump of cheese from the fridge because there was nothing else in there. And a bottle of Jolt cola.

And certainly not quiche.

Oooh, found this on wiki on Hex

There is also a mouse (pun for a computer pointer) that has built its nest in the middle of Hex. It doesn't seem to do anything, but Hex stops working if it is removed, or if Ponder forgets to feed it cheese.

?redo from start is a old MS basic error code. and the +++ was used as part of a command code set. So I think pratchet was just adding something that looked like a modern computer error to HEX and of course the mouse needed cheese!

Serious Pratchett fan here. The mouse is part of Hex, Hex will NOT work without it. When the mouse is out of cheese, Hex fails to function, and starts over. Kind of like running out of RAM, causing the machine to lock up and start over.

?redo from start is a old MS basic error code. and the +++ was used as part of a command code set

Yes, Hex doesn't crash for the same reasons as modern machines, he crashes because the mouse is hungry. It's an "out of memory" type error, Discworld style.

The MELON MELON MELON bit started after Hex dealt with the Bursar, a wizard with serious psychological issues, he caught the crazy from the Bursar, who is VERY rational, until he suddenly isn't, and goes utterly random. all of the quoted stuff above

+++Mr. Jelly! Mr. Jelly!+++
+++Error At Address: 14, Treacle Mine Road, Ankh-Morpork+++
+++MELON MELON MELON+++
+++Divide By Cucumber Error. Please Reinstall Universe And Reboot +++
+++Whoops! Here Comes The Cheese! +++
+++Oneoneoneoneoneoneone+++

is all the sort of stuff the Bursar says, not exactly, because Hex is a different brain that the Bursar, but the same type of weird. And Hex said it after they attempted to get Hex to psychoanalyze the Bursar. The crazy infected Hex. And when a machine goes crazy, it does things like make it's error codes get weird. "Error at address C/programfiles/nvidacorportaion/exe" is an address of an error my computer could report. So a Discworld machine reports an "Error At Address: 14, Treacle Mine Road, Ankh-Morpork" which is a street address there (I think it's the police station, if not, it's close to it.)


:D

Some seem to me to be general absurdity, akin to Monty Python-esqe slapping someone in the face with a fish, whereas others are inspired by legitimate computer errors and made absurd in typical Discworld fashion.

I'd say these ones are possibly just general absurdity:
+++Mr. Jelly! Mr. Jelly!+++
+++MELON MELON MELON+++
+++Whoops! Here Comes The Cheese! +++
(this last one would also be a boomerang joke to the "out of cheese error" - i.e. general absurdity but also, a callback to the previous joke)

As others mentioned, the "out of cheese error" is a Discworld version of the ubiquitous "Out of memory" errors (or the more generalized "Out of [resource]" errors, where 'resource' can be harddrive memory, RAM, network ports, file handles, etc; but memory (RAM or harddrive) is the most common and most well-known to non-programmers).

Recently while programming I had to deal with an Out of Memory error that was plaguing me on and off for about 3 months. They are very common, though less and less so (or at least, less visible to consumers), now that even cheap computers come with plenty of RAM.

(As an over-generalized simplification, RAM is memory that computers use to actively operate (and gets erased every time you shut down your computer), and the harddrive stores memory users want to save, such as files like photos and documents)

Here's a few other explanations to errors Pearl Sutton mentioned above:
+++Error At Address: 14, Treacle Mine Road, Ankh-Morpork+++

In computer RAM memory (its "thinking/operating" memory), an 'address' is the location of a particular piece of memory the computer is operating on. The address is a number, measured in bytes, that starts from 0 (in theory) up to the max amount of RAM you have. For example, from 0 up to 8,589,934,592 bytes (8 GB of RAM).

If there is an error at a specific address, it's not uncommon for an error to say something like, "Error at 0x075BCD15: <explanation of error>"
Instead, in Discworld, the 'address' outputted wasn't a memory address in bytes, but a street address (like "325 Broadway, New York City, New York"), as if the error occurred somewhere else in the world and you'd have to go there to fix the error.

It also leaves out the explanation of the error - which is part of the overall theme of the jokes: That none of these errors are remotely helpful in figuring out what went wrong (except perhaps the out of cheese one).
This is a common complaint with programmers, and computer users: that error messages are often unhelpful, and sometimes even deceptively misleading. Though, in recent years, some great effort has been made to improve the quality of error messages, but for *decades and decades*, error messages were stupidly opaque and often misleading. This is proven by even experienced programmers' first impulse being to first google the error message in the hope someone online can explain it in english, as the error message utterly fails to communicate what is wrong until someone has encountered the error enough times to be familiar with it.

Programmers usually specify byte addresses in hexadecimal form: 0x075BCD15 in base 16 (hexadecimal) is the number 123,456,789 in base 10 (decimal).
This also explains the computer's name, HEX. HEX is a pun, because it's both hexadecimal (a programmer's preferred method of counting bytes) and a wizard's hex (a curse/spell).

Decimal, how humans normally count, means we use 10 symbols to represent values. 0,1,2,3,4,5,6,7,8,9
Each additional position, is one power higher. 123 = 1 * (10 * 10) + 2 * (10) + 3    (123 = 1(10^2) + 2(10^1) + 3(10^0))
(In grade school, I remember them calling it "the one's place", "the ten's place", "the hundred's place")

Hexadecimal uses 16 symbols: 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F      (A = 10, B = 11, etc...)
Each additional position, is one power higher. A2F = A * (16 * 16) + 2 * (16) + F    (A2F = A(16^2) + 2(16^1) + F(16^0))

Programmers also count in binary. Binary is base 2, where everything is described with just two symbols: 0 and 1
This means numbers like decimal 123,456,789 are described as 0111 0101 1011 1100 1101 0001 0101

This following joke is reference to binary, but hilariously spells out the numbers:

+++Oneoneoneoneoneoneone+++

It's also possibly a callback to early internet culture.

Some people, when they get excited about something, type in way too many exclamation marks onto a sentence.
e.g: "I can't believe he did that!!!"

To type an exclamation mark on USA QWERTY keyboards, you hold shift and type the number '1'. (Shift + 1 = '!')

Sometimes they are so excited, they'd mistype some of their exclamation marks as the '1' instead of '!')
e.g: "I can't believe he did that!!1!!"

So other people started mocking or parodying that excitement, by adding 0's also, as if they were so excited, they accidentally (and ridiculously) started typing binary:
e.g: "I can't believe he did that!!10010101!!"

As that meme grew, people even began spelling out some of the letters, to take the absurdity up to eleven.
e.g: "I can't believe he did that!10one1!zero01one01!!"

Terry Pratchett was very familiar with internet culture and tech in general (many internet websites attempt to immortalize him by injecting his name (invisibly) into the webpages displayed by many websites).

+++Divide By Cucumber Error. Please Reinstall Universe And Reboot +++

This is a three-for-one error message. It's combining three separate error messages in one, so I'm going to break it apart to explain:

Divide By Cucumber Error.

In math, you can't divide something by zero. 5 divided by 0 is nonsense in math, and is called 'undefined' by mathematicians - i.e. they don't know what the answer should be.

In programming, it's even worse. An accidental divide-by-zero often crashes an entire program, or throws a nasty type of error called an 'exception'. In older computers, it'd even crash the entire computer. If such an error occurs, the program can 'catch' the 'exception', prevent the crash, and display an error message. Almost always they'd just say, "Divide by Zero Error" or similar, and to someone using the program, they wouldn't have a clue what caused the crash.
Heck, even as a programmer writing the code, I once spent three days hunting down where a divide-by-zero error even occurred.

Terry Pratchett made this Discworld error even more opaque and absurd by making it a 'Divide by Cucumber'.

Please Reinstall [program] And Reboot

Sometimes, especially in the earlier days of computer (but can still occur), a program can mess itself up so badly (due to bugs or other mistakes), it messes up it's own files in such a way that it can't recover itself. They'd then pop up an error saying, "Please reinstall [program name] and reboot" (rebooting was required to make the installation fully take affect). For example, "Please reinstall Adobe Acrobat and reboot".

This would be a nuisance, as you'd have to stop what you're doing, hunt through your installation discs and find the program to install (or find the download online and wait for it to download), wait for it to install, and reboot everything.

Please Reinstall Universe

Sometimes, worse than reinstalling a program, would be having to reinstall the entire Windows operating system. No error message would tell you to do that, afaik, but many support companies would say that, and sometimes online forums would advise that. Especially if you got infected by the worse kind of viruses, known as 'rootkits', that antivirus programs can't remove, and the only solution is to, as techy people like to say, "nuke it from orbit" by reinstalling Windows from scratch.

Reinstalling Windows is a huge nuisance, and basically ruins your entire day. You'd have to back up your files first, and installing Windows would sometimes take three hours or more to install, and unless you've taken precautions in advance, you'd have to then reinstall all your (several dozen) programs one by one, hunting for your CD keys and registration info, and then load your backed up files back onto the PC.

"Please Reinstall Universe" is a reference to this, as internet users would sometimes joke about how extreme and annoying this was - you'd have to reinstall everything from scratch, from bottom up. Your entire day, or two, would be shot to ruins.