1. Central Processing Unit
The CPU
Central Processing Unit

2. The Computer System Remember our computer system? CPU Input Unit
Output Unit
Memory (RAM)
Unit

3. CPU Now we take a closer look inside the CPU CPU Arithmetic and
Logic (ALU)
Control

4. Executing Instructions
All instructions in a computer are either control instructions or arithmetic/logic instructions
So each instruction is either handled by the ALU or the control unit

5. ALU
Most computer operations are executed in the arithmetic and logic unit or ALU
The ALU is responsible for performing mathematical as well as logical operations
Mathematical operations include addition, subtraction, division, multiplication, modulo
Logical operations include evaluating conditions

6. Control Unit The control unit is the nerve centre of the computer
It handles instructions dealing with control signals
You can think of the control unit as a manager that controls information flow in a computer

7. Computer Performance
The most important measure of a computer is how quickly it can execute programs
The processor is controlled by a clock where one basic instruction is completed in one clock cycle
So if a clock cycle is shorter, then the computer takes less time to execute a basic instruction

8. Which means we would have a FASTER computer!

9. Computer Performance Let P be the length of one clock cycle
The measure of a computer is the clock rate, R = 1/ P
Thus, when P is small, R is large

10. Computer Performance R is measured in cycles per second or Hertz (Hz)
Computers today have clock rates in the billions
The term “million” is denoted by the prefix Mega (M) and “billion” by Giga (G)

11. Computer Performance
So a 500 MHz processor operates at 500 million cycles per second
A 2 GHz processor operates at 2 billion cycles per second
This is the number of basic instructions the processor can go through in 1 second

12. Practice
How long does it take a computer to execute a basic instruction if the processor clock rate is 3.2 GHz?
If a processor can execute a basic instruction in 0.8 ns (nanoseconds), what is the clock rate of the computer?