You don't have to know, and many working on Manframes don't. No-one outside the Mainframe should need to know, unless you get the stupid "oh, but they refuse to

You don't have to know, and many working on Manframes don't. No-one outside the Mainframe should need to know, unless you get the stupid "oh, but they refuse to change the program" for a data-transfer (read, "we signed-off on it before we knew what we were doing"). There's 256 bit-patterns to a byte. It is not rocket surgery.