The Central Processing Unit (CPU) is often described as the “brain of the computer,” but this description can feel vague to IB Computer Science students. To score well in exams, students must understand how the CPU actually processes data, not just memorise definitions.
In IB Computer Science, the CPU is studied as a system made up of key components, each with a specific role. Understanding how these components work together is essential for questions on computer architecture, performance, and the fetch–decode–execute cycle.
What Is the CPU?
The CPU is responsible for:
- Executing program instructions
- Performing calculations
- Controlling data flow within the computer
Every instruction a program runs — from adding numbers to loading a file — passes through the CPU.
In IB Computer Science, the CPU is usually explained using three core components:
- The Arithmetic Logic Unit (ALU)
- The Control Unit (CU)
- Registers
The Arithmetic Logic Unit (ALU)
The ALU is the part of the CPU that performs calculations and logical operations.
It is responsible for:
- Arithmetic operations (addition, subtraction, multiplication, division)
- Logical operations (AND, OR, NOT, comparisons)
For example, when a program checks whether one value is greater than another, the ALU performs that comparison.
IB exam questions often test whether students understand that:
- The ALU does not control program flow
- The ALU only performs operations requested by instructions
