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Many machine code and assembly instructions contain two parts:

• the opcode - this is the actual instruction
• the operand - this is a value that the instruction uses or manipulates

Both values are represented either in binary or hexadecimal. Hexadecimal is popular with programmers because it can represent larger values in fewer characters. For example, denary 250 is 11111010 in binary but only FA in hexadecimal. Hexadecimal is therefore easier to read and understand by humans.

Consider this simple machine code program:

901 - inputs a value

306 - stores it in memory address 06

5A1 - loads into the accumulator the value held in memory address A1

Each of these instructions has an opcode and an operand: