The Control Unit
The control unit sends out signals that fetch instructions from the main memory. The control unit is responsible for running programs that are loaded into the main memory.
To understand these instructions:
Carry out the instructions that arer fetched from the main memory.
The Arithmatic and Logic Unit (ALU)
The ALU carries out the computers arithmatic functions such as addition, subtraction, multiplication etc.
It carries out the computers logical functions such as comparing values using IF, AND, >, < and WHILE.