1. Central Processing Unit (CPU)
The Central Processing Unit is the ‘brain’ of a computer
system. It executes all program instructions and
commands. It controls data and all devices in a computer
system
It consists of 3 main parts:
1. Control unit (CU)
2. Arithmetic and Logic unit
(ALU)
3. Registers

2. Inside the CPU
Address bus
Memory
Address
Other Register
registers
Data bus
Memory
Main
Data
Memory
Register
Control Bus (Read / Write)
Arithmetic
Logic Unit Control Unit
(ALU) (CU)
Clock pulses
Electronic
clock

3. The Control Unit
The CU sends signals to other parts of the computer. It
manages fetch, decode and execute program
instructions
It synchronises the whole system by telling devices
what to do and when to do it

4. The Arithmetic Logic Unit
The ALU is the place where data processing
occurs.
Processing any data in the ALU
involves some arithmetic calculations
such as add, subtract, multiply or
divide. It also involves logical
comparisons like AND, OR
The ALU uses special arithmetic registers
to temporarily store data and results of
calculations

5. The Registers
The Registers are very fast storage locations inside the processor
itself. There are many registers including :
• memory address register (MAR) –
holds the address of a location in
memory
• memory data register (MDR) – holds
data just read from or written to memory
• program counter (PC) – holds the
address of the next instruction to be
fetched
• Instruction register (IR) – holds the
current instruction being executed
• general purpose registers – can be
used by programmers