Central Processing Unit The CPU Central Processing Unit

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

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

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

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

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

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

Which means we would have a FASTER computer!

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

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)

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

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?