If you’re talking about compilers and such program that make programming languages usable.
Usually an older language.
For example Java’s first compilers were written in the programming language C.
C seem to be the one a lot of languages were written in, because it’s both very fast and very old.
Older languages such as C were written in Assembly Language.
Each assembly language only works on a certain kind of processor it runs on, and we’re running into the dark ages before they were pretty standardized. It’s just one step above the machine code that basically telling the processor what to do. And include some bear minimum stuff for a human to use it a lot and remain sane.
That step above machine code was made by programmers actually figuring out what exactly they wanted the processor to do in machine code, in order to make the first assemblers (thing that makes assembly code into machine code).
Anything lower and you’re talking with the chip guys connecting wires.
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