Programming

For those curious about the real answer, this is called compiler bootstrapping. If you want to write the first C compiler for a computer architecture you first write a very small compiler in machine code that can handle a very small subset of C. Just the most basic features. Then you use that to write a compiler in that simplified C that can handle more of the features. Do this a couple more times and you've got a C compiler written in C.

At the beginning, there were wires and dials that people would plug on the computer.

Or, rather, punched cards are older than the wires. The first electronic computers didn't use them, but the mechanical ones did.