Q.What does directive do?

A computer program is an ordered sequence of binary operations — storing and retrieving data, adding, subtracting, and applying Boolean logic — that the CPU executes; the program itself is stored in memory rather than in the CPU. Every instruction is built from an opcode (the "verb" that says what to do) and an operand (the "noun", the data it acts on). The memory locations the CPU reads and writes under program control are the data addresses, and their contents are data numbers.

Machine language is pure binary code. It is what the CPU actually runs, but it is almost impossible for people to read or write directly. Assembly language is the human-friendly bridge: each machine instruction is written as a short mnemonic (such as ADD or MOV), and an assembler translates these mnemonics into machine code. Because assembly deals directly with the CPU's internal registers and memory, it is called a low-level language. …