1. GCSE COMPUTER SCIENCE
Topic 4 - Computers
4.2 Hardware

2. This presentation covers the following content from the specification
Students should:
4.2.1 understand the function of the hardware components of a computer system (CPU, main memory, secondary storage, input and output devices) and how they work together
4.2.2 understand the function of different types of main memory (RAM, ROM, cache)
4.2.3 understand the concept of a stored program and the role of components of the CPU (control unit (CU), arithmetic/logic unit (ALU), registers, clock, address bus, data bus, control bus) in the fetch-decode-execute cycle (the Von Neumann model)
4.2.4 understand how data is stored on physical devices (magnetic, optical, solid state)
4.2.5 understand the concept of storing data in the ‘cloud’ and other contemporary secondary storage
4.2.6 understand the need for embedded systems and their functions

3. Hardware
These are the physical parts of the computer, the parts that you can touch
This can include input and output devices as well as peripherals
A peripheral is anything that you can plug in or attach to a computer

4. Components
The internal parts of the system that deals with the inputs and outputs are known as the components:
What’s in here?

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PC Components
Motherboard
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The motherboard allows all of the other components to communicate with each other. The components plug into the motherboard allowing for easy upgrades.

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PC Components
CPU
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Also known as the Central Processing Unit or simply as the Processor.
The processor carries out all the arithmetic calculations and logic operations of a computer. Think of it as the ‘brain’ of a computer.

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PC Components
Memory
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The memory is where all the current information being worked on is stored. This could be applications (instructions) or data.

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PC Components
Hard Disk Drive
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A permanent storage of the operating system, applications and users’ files.

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PC Components
Graphics Card
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Allows more complex graphics to be displayed. Often required for games or 3D applications.

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PC Components
PSU
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The power supply unit supplies power to the motherboard which in turn, supplies power to the other components in a computer system.

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PC Components
Sound Card
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The sound card allows digital sound to be output from speakers connected to a computer.

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PC Components
Input Devices
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Input devices allow you (the user) to give the computer information.

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PC Components
Output Devices
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Output devices allow the computer to display processed information to you (the user).

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PC Components
Storage Devices
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Storage devices allow users to save their work long term, when the power is turned off these devices to not lose the information.

15. Component Descriptions Found in the Python folder
Activity 1
Component Descriptions
You need to understand what role each of the main components play in a computer system.
Complete an electronic version of this worksheet, found under lesson 4.2 on the website.
Found in the Python folder

16. Write down what RAM and ROM stand for.
Primary Memory
This is storage that the CPU (processor) can access directly. There are two types of primary memory:
RAM
Random Access Memory
ROM
Read Only Memory
Write down what RAM and ROM stand for.

17. Activity 2
Fill in the blanks
Write out the following sentences about memory and fill in the blanks.
Primary memory is storage that the CPU can access __________. There are two main types of primary memory; __________ and __________ .
Words to use: RAM, directly, ROM

18. RAM
RAM is used to store the programs (applications) and data the computer is currently working on.
RAM is volatile, this means that it is wiped when the power is turned off.
The more RAM a computer has, the more programs and data it can run at the same time without it slowing down.

19. Words to use: volatile, slowing, programs, off
Activity 3
RAM is used to store the __________ and data the computer is currently working on. RAM is __________ , this means that it is wiped when the power is turned __________ . The more RAM a computer has, the more programs and data it can deal with at the same time without __________ down.
Words to use: volatile, slowing, programs, off

20. ROM
When a computer is turned on it needs to start fetching and executing instructions.
The problem is that RAM is blank when the computer is turned on.
The ROM contains the program that is used to start up the computer. This is known as the ‘boot’ program.
In many systems the boot program is known as the BIOS (Basic Input Output System).
The program inside the ROM is not easily changed or deleted.

21. Words to use: program, boot, deleted, BIOS, computer, read
Activity 4
ROM stands for __________ Only Memory. This is not easily changed or __________. The ROM contains the __________ to start up the __________. This is also known as the __________ program. Sometimes also referred to as the __________ (Basic Input Output System).
Words to use: program, boot, deleted, BIOS, computer, read

22. Cache Cache is super fast memory
A computer system usually has only a small amount
It is located between the CPU and the RAM
CPU (Processor)
RAM (Memory)
Cache

23. Buses
Buses
The CPU is connected to the other components by wiring known as buses.
There are three buses:
Address Bus
Data Bus
Control Bus
They are used to carry data around the CPU and other components.

24. Activity 5
Buses
CPU ?
Input / Output Devices …
Buses
Memory

25. Activity 6
Using your diagram from the previous activity, complete the table below by identifying the name of each bus from the description: address, data & control busses
Description
Name
Sends and receives signals that control the CPU and other parts of the computer system.
Control Bus
Carries the address of memory locations used to store data and program instructions.
Address Bus
Transfers the binary data around the computer.
Data Bus

26. Inside the CPU

27. Inside the CPU

28. Arithmetic and Logic Unit (ALU)
Inside the CPU
The CPU comprises three main components: the control unit, the Arithmetic and Logic Unit (ALU) and the registers.
Arithmetic and Logic Unit (ALU)
Registers
Control Unit

29. Arithmetic and Logic Unit (ALU)
Inside the CPU
The control unit sends out signals to other parts of the computer system and is responsible for organising the fetching, decoding and execution of instructions.
Arithmetic and Logic Unit (ALU)
Registers
Control Unit

30. Arithmetic and Logic Unit (ALU)
Inside the CPU
The ALU carries out arithmetic operations (+, -, * , /, etc.) and logic operations (AND, NOT, etc.) It can include the ability to compare a number with zero or to test if two numbers are equal.
Arithmetic and Logic Unit (ALU)
Registers
Control Unit

31. Arithmetic and Logic Unit (ALU)
Inside the CPU
The registers are individual storage locations which hold an instruction, data or address of a memory location.
Each type of processor has a number of different registers each designed for a specific function to hold a particular bit of information.
Arithmetic and Logic Unit (ALU)
Registers
Control Unit

32. Arithmetic and Logic Unit (ALU)
Inside the CPU
Most processors have
the following
registers:
The ‘instruction
register’.
The ‘accumulator’.
The ‘program counter’.
Arithmetic and Logic Unit (ALU)
Registers
Instruction Register
Accumulator
Program Counter
Control Unit

33. Inside the CPU Registers Arithmetic and Logic Unit (ALU) Control Unit
The instruction
register holds the
instruction that is currently being executed by the processor.
Arithmetic and Logic Unit (ALU)
Registers
Instruction Register
Accumulator
Program Counter
Control Unit

34. Arithmetic and Logic Unit (ALU)
Inside the CPU
The accumulator is a register that holds the accumulated total of results performed in the ALU.
Arithmetic and Logic Unit (ALU)
Registers
Instruction Register
Accumulator
Program Counter
Control Unit

35. Arithmetic and Logic Unit (ALU)
Inside the CPU
The program counter is a register that holds the memory address of the next instruction to be executed.
Arithmetic and Logic Unit (ALU)
Registers
Instruction Register
Accumulator
Program Counter
Control Unit

36. Activity 7 Parts of the CPU
Use these labels to complete the diagram: Memory, Control Unit, Arithmetic and Logic Unit (ALU) and Registers.
PROCESSOR
Memory
Control bus
Control Unit
ALU
Address bus
Registers
Data bus

37. Using arrows match each label to the correct part of the processor.
Activity 8
Using arrows match each label to the correct part of the processor.
Accumulator register
Holds the accumulated total of results performed in the ALU
Control unit
Sends out signals to other parts of the computer system and fetches, decodes and executes instructions
Registers
Individual storage locations which hold an instruction, data or address of a memory location
Arithmetic and logic unit (ALU)
Carries out arithmetic and logic operations
Program counter register
Holds the address of the main memory location storing the next instruction
Instruction register
Holds the instruction that is currently being executed by the processor
PROCESSOR
Memory
Control bus
Control Unit
ALU
Address bus
Data bus

38. The Stored Program Concept
This means:
Both the instructions and data for a program are stored in main memory
Instructions and data are stored in binary code
Instructions and data are fetched, decoded and executed in a sequence by the CPU
ACTIVITY
Write this information in your book

39. The Fetch-Decode-Execute Cycle
Activity 10
The Fetch-Decode-Execute Cycle
Draw and label the diagram of the fetch-decode execute cycle using these words and descriptions below:
- Fetch
- Decode
- Execute
Fetch
- Fetches the next instruction from memory and increments the program counter
- Decodes the bit pattern (machine code) into the instruction to be executed
- Executes the instruction and stores the results in memory or registers
Execute
Decode

40. Steps of the Fetch-Decode-Execute Cycle
Activity 11
Steps of the Fetch-Decode-Execute Cycle
Description
Order
Increment the program counter to point to the next instruction 6
Decode the instruction 2
Store results in a register 5
If the instruction uses data from memory, identify the memory addresses and fetch the data from memory 3
Fetch the next instruction from main memory using the memory address in the program counter register 1
Execute the instruction 4

41. How it impacts on performance
Activity 12
Describe each of these factors and explain how they impact on CPU performance:
Factor
What is it?
How it impacts on performance
Clock Speed
The clock speed indicates how fast the CPU can run. This is measured in Hertz (Hz) and shows how many instruction cycles the CPU can deal with in one second. A 2 GHz CPU performs two billion cycles a second.
Higher clock speed indicates that the processor can work faster. It can perform more fetch-decode- execute cycles per second. A faster CPU uses more energy and creates more heat.
Number of Cores
A CPU can contain one or more processing units. Each unit is called a core. A core contains an ALU, control unit and registers. It is common for computers to have two (dual), four (quad) or even more cores.
CPUs with multiple cores have more power to run multiple programs at the same time. However, doubling the number of cores will not simply double a computer's speed.
Cache Size
Cache is a small amount of memory which is a part of the CPU. It is used to temporarily hold instructions and data that the CPU is likely to reuse.
The more cache there is, the more data can be stored closer to the CPU and access quickly. This means the CPU takes less time fetching instructions and data, thus processing quicker.

42. Secondary Storage
These devices allow data to be stored when not in use by the CPU.
They are non-volatile so the data is not lost when the computer is turned off.
They also allow users to transfer data from one computer to another.
When data in secondary storage needs to be used, it needs to be transferred to the primary memory.
There are two types: Internal and Removable

43. Example: Hard disk drive.
Internal and Removable
Internal
Internal storage devices are built into the computer. They are used to store the operating system, programs and files.
Example: Hard disk drive.
Removable
Refers to storage that can be taken away from the computer and used on another computer.
Sometimes the device itself is not removed from the computer, only the medium on which the data is stored is removed not the drive.
Example: CDs and DVDs

44. Words to use: non-volatile, memory, data, transfer, primary
Activity 13
Fill in the blanks
Write out the following sentences about secondary storage and fill in the blanks.
Secondary Storage: These devices allow __________ to be stored when not in use by the CPU. They are __________ so the data is not lost when the computer is turned off. They also allow users to __________ data from one computer to another. When data in secondary storage needs to be used, it needs to be transferred from the __________ __________ .
Words to use: non-volatile, memory, data, transfer, primary

45. Words to use: store, another, computer, removed
Activity 14
Fill in the blanks
Write out the following sentences about storage and fill in the blanks.
Internal & Removable Storage: Internal storage devices are built into the __________ . They are used to __________ the operating system, programs and files. Refers to storage that can be taken away from the computer and used on __________ computer. Sometimes the device itself is not __________ from the computer, only the medium on which the data is stored (e.g. a CD) is removed not the drive.
Words to use: store, another, computer, removed

46. Magnetic Storage Hard Disk Drive Floppy Disks
Feature a spinning disc and a moving head that can either magnetise or demagnetise any part of the disk.
1s are represented by the magnetised parts of the disc.
0s are represented by the demagnetised parts of the disc.
Hard Disk Drive
Floppy Disks

47. Words to use: demagnetise, magnetised, demagnetised, magnetise, disc
Activity 15
Fill in the blanks
Write out the following sentences about magnetic storage and fill in the blanks.
Magnetic Storage: Feature a spinning __________ and a moving head that can either __________ or __________ any part of the disk. 1s are represented by the __________ parts of the disc. 0s are represented by the __________ parts of the disc.
Words to use: demagnetise, magnetised, demagnetised, magnetise, disc

48. The data is stored on a reflective disk.
Optical Storage
The data is stored on a reflective disk.
0s are represented by altering parts of the disc so they don’t reflect a laser beam
1s are represented by parts that haven’t been altered and still reflect a beam.
CDs
DVDs
Blu-Rays

49. Words to use: laser, reflect, beam, reflective
Activity 16
Fill in the blanks
Write out the following sentences about optical storage and fill in the blanks.
Optical Storage: The data is stored on a __________ disk. 0s are represented by altering parts of the disc so they don’t reflect a __________ __________ . 1s are represented by parts that haven’t been altered and still __________ a laser beam.
Words to use: laser, reflect, beam, reflective

50. Solid State Storage Internal Drives Memory Sticks Memory Cards
The term solid-state refers to all devices that use flash memory.
They are ‘solid-state’ because they have no moving parts.
This is useful for portable devices that need to be carried around. They are also faster and more reliable.
Internal Drives
Memory Sticks
Memory Cards

51. Words to use: moving, portable, flash
Activity 17
Fill in the blanks
Write out the following sentences about solid state storage and fill in the blanks.
Solid-State Storage: The term solid-state refers to all devices that use __________ memory. They are ‘solid-state’ because they have no __________ parts. This is useful for __________ devices that need to be carried around. They are also faster and more reliable.
Words to use: moving, portable, flash

52. Cloud storage has many advantages and disadvantages
What Is It?
Storage that uses an Internet connection to store your files on servers based elsewhere in the world
Common commercial examples include: Dropbox, Apple iCloud, Google Drive, MS OneDrive, Amazon Cloud
Cloud storage has many advantages and disadvantages

53. Cloud Storage Advantages and Disadvantages Advantages Disadvantages
Many services offer unlimited storage
Requires a reliable Internet connection
Automatic Backup
Requires a medium to fast Internet connection
Universal Access
Large bandwidth use
Device Independence
User has less control over the data
List these advantages and disadvantages in your workbook

54. What Are Embedded Systems?
A computer designed to do a specific task
Small, low cost and relatively simple
Common appliances include: Washing machines, microwaves, TV remotes, toys, ATMS, vending machines etc.
PCs are general purpose whereas embedded systems perform specific tasks