The document discusses instruction codes in computers. It explains that an instruction code consists of an operation code and operands. The operation code specifies the operation to perform like add, subtract, etc. The operands specify the data on which the operation acts, which can be stored in registers or memory. The document outlines the three main types of instruction codes - memory reference, register reference, and input/output instructions. It explains how the computer determines the type of instruction and provides a table of instructions for the basic computer.