1. GCSE
OCR
Computing
A451
The CPU
2-1-2 Computing hardware 1

2. Objectives State the purpose of the CPU
Describe the function of the CPU as fetching and executing instructions stored in memory
Explain how common characteristics of CPUs such as clock speed, cache size and number of cores affect their performance

3. What is this?

4. The CPU

5. Central Processing Unit (CPU)
The Central Processing Unit or CPU is arguably the most important component of a computer
What does it do?
If it was one organ in the human body what would it be?

6. Central Processing Unit (CPU)
You can think of the CPU is being like the brain in a human
It is responsible for all of a computers processing

7. The main components of a computer
MAIN MEMORY
AUXILIARY
STORAGE
CENTRAL PROCESSING
UNIT (CPU)
INPUT
DEVICES
OUTPUT

8. The purpose of the CPU The Control Unit The ALU Registers Cache
The CPU is split into many parts internally
Two of its major parts are:
The Control Unit
The ALU
Registers
Cache
Control Unit
Arithmetic Logic Unit (ALU)
Main Memory (RAM)
Central Components of a Computer
CPU
Registers
Cache

9. Arithmetic Logic Unit (ALU)
Performs two sorts of operations on data:
Arithmetic operations
addition, subtraction, multiplication, division
Logical operations
comparing one data item to another: is it smaller than, greater than or equal to?

10. The Control Unit
“The control unit co-ordinates and controls all the operations carried out by the computer.”
Controls and monitors hardware attached to the system
Controls input and output of data
Controls the flow of data within the CPU

11. Registers Little storage locations that hold one instruction.
These are there waiting to be processed
Once processed the registers are deleted and the process starts again.

12. Cache Short term volatile memory
Speeds up the process of the computer as the cache is in the CPU
3 Mb capacity

13. The Fetch - Decode - Execute cycle

14. Perform an arithmetic or logical operation
The Fetch - Decode - Execute cycle
Fetch Step
Execute Step
Main
Memory
Load data from memory
Store data in memory
Perform an arithmetic or logical operation
Decode Step
CPU
Program Counter

15. Fetch – Decode – Execute
The CPU operates by repeating three operations:
FETCH – causes the next instruction and any data involved to be fetched from main memory
DECODE – decodes the instruction to make sure it can be carried out
EXECUTE – carries out the instruction
Repeat…

16. What affects CPU performance?
The following are three of the most common factors which can affect a CPU’s performance
Clock Speed
Number of Cores
Cache Size
Which have you heard of?
Can you explain them?

17. Factors affecting CPU performance
Clock speed
Cache size
Cycles per second
measured in hertz
Superfast working memory
Number of cores
The number of duplicate
CPUs on a single chip

18. Processor Speed How fast is your computer’s processor?
One cycle per second = 1 Hertz (Hz) = 1 instruction carried out each second
1 Kilohertz (KHz) = 1024 cycles per second
1 Megahertz (MHz) = 1,048,576 cycles per second
1 Gigahertz (GHz) = 1,073,741,824 cycles per second (Approximately 1 billion!)
How fast is your computer’s processor?

19. Cache memory Cache is a small amount of memory in or near the CPU
When an instruction is fetched from main memory it is copied into the cache so if it is needed again soon after, it can be fetched from the cache instead which is much quicker than going back to main memory
CPU
Cache
Main Memory

20. Which is faster?
A dual core processor running at 2.7GHz with 4Mb of shared Level 3 Cache
A quad core processor running at 1.5GHz with 8Mb of shared Level 3 Cache
A single core processor running at 3.2GHz with 2Mb of shared Level 3 Cache
A dual core processor running at 3.2GHz with 4Mb of shared Level 3 Cache
Calculate the maximum number of cycles per second in each case and rank them in order of performance

21. Worksheet 1
The Central Processing Unit

22. Plenary What is the main purpose of the CPU? How does the CPU operate?
Name three common factors which affect how fast a CPU can perform