On IBM mainframe computers running the zOS operating system, there is a series of error codes that are represented by three hexadecimal (base-16) numbers. They begin with the number zero and the letter C. The actual error is indicated by the third digit. The first of these is called an operation exception; it's code is 0C1. Strictly speaking, it should be pronounced zero-cee-one but most of us say it oh-cee-one. Get it? Hilarious, huh?