In the late 70s the Apple ][ came with a manual with a terse but just good enough description of the 6502 and its opcodes, especially when combined with the sou

In the late 70s the Apple ][ came with a manual with a terse but just good enough description of the 6502 and its opcodes, especially when combined with the source code for the machine's ROM. At least it was good enough for 17 year old me, who had never seen a computer before, to write some useful programs in 6502 machine code. One of the first was something that replaced ("shimmed") the standard keyboard input function with code that fed text to the printer from a file on floppy disk whenever the computer was waiting for user input. Given the usual small buffer in the printer that meant the printer hardly ever stopped.