The CPU System
The brain of every computer system. Understand the purpose of the Central Processing Unit, its internal components, and the relentless Fetch-Decode-Execute cycle.
Concept Explorer: The FDE Step-Through
Click the button to manually step through one complete cycle. The CPU does this billions of times every single second!
Internal Components
ALU
Arithmetic Logic Unit
Performs all mathematical calculations (+, -, /, *) and logical comparisons (AND, OR, NOT).
CU
Control Unit
It controls and synchronises the hardware, and crucially, it is responsible for decoding the instructions.
Cache
High Speed Memory
Extremely fast memory built inside the CPU used to store the most frequently used instructions and data.
Check Your Understanding
1. Which component within the CPU is entirely responsible for decoding an instruction?
2. An algorithm checks if a player's score is > 100. Where does this validation comparison physically occur?
Written Exam Scenario (AO2/AO3)
"Explain how the Control Unit and the Arithmetic Logic Unit work together during the execution of a mathematical calculation." (4 marks)
The CU triggers the process: The Control Unit decodes the instruction to determine that it is a mathematical operation.
The CU delegates: The Control Unit then sends control signals directing the ALU to prepare for the calculation.
The ALU executes: The Arithmetic Logic Unit carries out the actual mathematical calculation.
The Result: The resulting value is typically placed into the Accumulator, completing the Execute stage before the cycle repeats.