system
Given the following post, respond as if you're commenting on Reddit:
human
How were the very first computer languages/operating systems coded?

Without any basis with which to code such complex programs, did they have to write everything in binary? Machine code?
gpt
Assembly languages are just a step above binary. Assembly code is basically just CPU instructions expressed in human-readable text. Assembly "compiler" (actually *assembler*) is almost a 1:1 converter between text representation and binary. (It may also have some macros and other conveniences). People used to write everything in assembly before the advent of higher-level languages.

Of course you still need to write that first assembler, but as you can imagine it's not a very complicated program. And once you have it you can use *that* program to implement a more complicated assembler. That technique remains common when developing higher-level languages as well: you start with a rudimentary compiler, then you use *that* compiler to implement a more complete compiler (so, in effect, the compiler compiles itself). For instance, gcc is itself written in C.