craig’n’dave ocr gcse computer science terminology unit 1 · memory in the processor providing...

OCR GCSE Computer Science

Terminology

Unit 1 © CraignDave Ltd

Craig’n’Dave

Computer systems

80 marks

1 hour and 30 minutes

Written paper

(no calculators allowed)

Central processing unit

1.1 SYSTEMS ARCHITECTURE

Decodes and executes instructions.

Von Neumann Architecture

Instructions are fetched, decoded and

executed one at a time.

Instructions and data are held together in the

same memory space.

Memory Address Register

Holds the address of data ready for use by the

memory data register.

Or the address of an instruction passed from

the program counter.

Step 2 of the fetch, decode, execute cycle.

Memory Data Register

Holds the data fetched from or to be written to

the memory.

Program counter

Holds the address of the next instruction.

Accumulator

Holds the result of calculations.

Arithmetic logic unit

Performs calculations e.g. x = 2 + 3

and logical comparisons e.g. IF x > 3

in the CPU.

Control unit

Decodes instructions.

Sends signals to control how data moves

around the CPU.

Memory in the processor providing fast access

to frequently used instructions and data.

Factors affecting the speed of the CPU

Clock speed.

Number of cores.

Cache size.

Speed is not always increased because it

depends on the task and the size of the RAM.

Embedded system

A computer system within a larger mechanical

or electrical system designed for a

specialist purpose.

Example 1: Washing machine.

Example 2: Engine management system.

The order that the registers are used in the

von Neumann fetch, decode, execute cycle

To fetch an instruction:

1. Program Counter to the…

2. Memory Address Register to the…

3. Memory Data Register.

Decode may then require data so repeat steps

2 and 3. Results of calculations are stored in

the accumulator.

Random Access Memory

1.2 MEMORY

Volatile (data lost when power is off)

Read and write

Purpose: temporary store of currently

executing instructions and their data. E.g.

applications and the operating system in use.

1.2 MEMORY

Read Only Memory

1.2 MEMORY

Non-volatile (data retained when power is off)

Read only

Purpose: stores instructions for starting the

computer called the bootstrap.

1.2 MEMORY

Virtual memory

1.2 MEMORY

Using part of the hard disk as if it were random

access memory.

Allows more applications to be open than

physical memory could hold.

1.2 MEMORY

Flash memory

1.2 MEMORY

Solid state (no moving parts).

Faster than a hard disk drive.

Robust.

Used to store the BIOS.

1.2 MEMORY

Secondary storage

1.3 STORAGE

Permanent storage of instructions and data

not in use by the processor.

Stores the operating system, applications and

data not in use.

Read/write and non-volatile.

1.3 STORAGE

How many 4MB pictures can be stored on a

64GB memory stick?

1.3 STORAGE

Using approximations for GB/MB:

64,000,000,000 divided by 4,000,000 =

16,000 pictures.

Can allow 10% for overheads, e.g. file table.

(14,400 in this situation)

1.3 STORAGE

How much capacity would be required to

store a 50,000 character word processed

document?

1.3 STORAGE

50,000 bytes (1 byte per character)

or 50 kilobytes

or 0.05 megabytes

Can allow 10% for overheads, e.g. formatting.

(55,000 bytes in this situation)

1.3 STORAGE

How much capacity in gigabytes would be

required to store an uncompressed 2 minute

full HD video (1920x1080) at 24 bit colour and

60 frames per second?

1.3 STORAGE

2 minutes = 120 seconds

60 frames per second x 120 = 7,200 frames

1,920 x 1,080 x 24 = 49,766,400 bits per frame

49,766,400 x 7,200 = 358,318,080,000 bits.

= 44.79 ≈ 45 gigabytes.

1.3 STORAGE

Optical storage

1.3 STORAGE

CD/R, CD/RW, DVD/R, DVD/RW

Use: music, films and archive files.

Low capacity.

Slow access speed.

High portability.

Prone to scratches.

Low cost.

1.3 STORAGE

Magnetic storage

1.3 STORAGE

Hard disk drive.

Use: operating system and applications.

High capacity.

Medium data access speed.

Low portability (except for portable drives).

Reliable but not durable.

Medium cost.

1.3 STORAGE

Solid state storage

1.3 STORAGE

Memory cards & solid state hard drive (SSD).

Use: digital cameras and smartphones.

Medium capacity.

High portability.

Reliable and durable. No moving parts.

Fast data access speed.

High cost.

1.3 STORAGE

Device most suitable for:

1. Skiing headcam

2. Video library

3. Free gift for a magazine

4. Portable games console

5. Engine management system

1.3 STORAGE

1. Solid state: durable, medium capacity.

2. Magnetic: high capacity.

3. Optical: low cost.

4. Solid state: medium capacity, portable.

5. Solid state: durable.

1.3 STORAGE

Local area network

1.4 WIRED AND WIRELESS NETWORKS

Small geographic area.

All the hardware for the LAN is owned by the

organisation using it.

Wired with UTP cable, fibre optic cable or

wireless using routers and Wi-Fi access points.

Wide area network

Large geographic area.

Infrastructure is hired from telecommunication

companies who own and manage it.

Connected with telephone lines, fibre optic

cables or satellite links.

Factors affecting the performance of a

network

Number of users.

Error rate.

Type of transmission media used.

Bandwidth.

Latency.

Client-server

A client makes requests to the server for data

and connections.

A server controls access and security to one

shared file store.

A server manages access to the internet,

shared printers and email services.

A server runs a backup of data.

Peer-to-peer

All computers are equal.

Computers serve their own files to each other.

Each computer is responsible for its own

security and backup.

Computers usually have their own printer.

Hardware to connect a local area network

Wireless access points to connect computers wirelessly.

Network interface card to connect a computer to the

wireless access point, switch or router.

Switches to connect computers and direct frames.

UTP cable (short distances, small bandwidth).

Fibre optic cable (longer distances, high bandwidth).

Router to connect to another network. E.g. Internet and

direct packets to destination on a network.

The Internet

A worldwide collection of computer networks.

Domain name server

Matches the URL of a web site into an IP

address of the web server.

Each web site has an address known as a URL.

Every web server has an IP address.

Humans then don’t need to remember IP

addresses, they can use more friendly URLs.

Hosting

Websites stored on dedicated servers.

Reasons include:

Websites need to be available 24/7.

Accessed by thousands of users at a time.

Strong protection from hackers.

They need an IP address that doesn’t change.

The cloud

Remote servers that store data that can be

accessed over the internet.

Advantages:

+ Access anytime, anywhere from any device.

+ Automatic backup.

+ Collaborate on files easily.

Virtual network

A logical software based network.

Advantages:

+ Increased security, including more secure

access to the network remotely.

+ The network can easily be expanded with less

impact on the infrastructure and cost.

+ Log in to work from home.

Star network

1.5 NETWORK TOPOLOGIES, PROTOCOLS & LAYERS

Computers connected to a

central switch.

If one computer fails no

others are affected.

If the switch fails all connections are affected.

SWITCH

Mesh network

Switches (LAN) or routers

(WAN) connected so

there is more than

one route to the

destination.

E.g. The Internet

More resilient to faults but more cable needed.

SWITCH SWITCH

Wireless connection to a network.

Requires a wireless access point or router.

Data is sent on a specific frequency.

Each frequency is called a channel.

Advantages and disadvantages of Wi-Fi over

wired connections

+ More convenient connections.

+ No cabling.

+ Useful for hard to reach places.

- Lower bandwidth.

- Suffers from interference.

- Less secure.

Encryption

Encoding readable data called plaintext into

unreadable data called ciphertext.

Only the intended recipient can decode the

data using a key.

Protects communications from hackers.

Ethernet

A standard for networking local area networks

using protocols.

Frames are used to transmit data.

A frame contains the source and destination

address, the data and error checking bits.

Uses twisted pair and fibre optic cables.

A switch connects computers together.

Protocol

A set of rules

for how computers communicate.

E.g. Speed of transmission and error checking.

TCP/IP

Transmission Control Protocol

Internet Protocol

TCP provides an error free transmission

between two routers.

IP routes packets across a wide area network.

Hyper Text Transfer Protocol

A client-server method of requesting and

delivering HTML web pages.

Used when the information on a web page is

not sensitive or personal.

Hyper Text Transfer Protocol Secure

Encryption and authentication for requesting

and delivering HTML web pages.

Used when sensitive form or database data

needs to be transferred.

E.g. passwords and bank account details.

File Transfer Protocol

Used for sending files between computers,

usually on a wide area network.

Typically used for uploading web pages and

associated files to a web server for hosting.

Post Office Protocol

Used by email clients to retrieve email from an

email server.

Internet Message Access Protocol

Used by mail clients to manage remote mail

boxes and retrieve a copy of an email from a

mail server.

Simple Mail Transfer Protocol

Sends email to an email server.

Layers

Dividing the complex task of networking into

smaller, simpler tasks.

How data is sent on a cable/wireless (layer 1).

IP routes a packet of data (layer 2).

TCP checks for errors in the packet (layer 3).

Packet switching

1. TCP splits data into smaller packets.

2. Each packet is given a number and an address.

3. Each packet takes its own route across the network.

4. Packets are received by the host server and checked.

5. A request for packets to be resent is sent if necessary.

6. Packets are assembled back into the correct order.

7. The request is processed by the server.

+ Maximises the use of the network. More secure as the

full data stream is not sent in the same direction.

Malware

1.6 SYSTEM SECURITY

Software written to cause loss of data,

encryption of data, fraud and identity theft:

virus, worm, trojan, ransomware and spyware.

Protect with: anti-malware software, backups,

staff training, network polices and installing

operating system updates.

1.6 SYSTEM SECURITY

Phishing

1.6 SYSTEM SECURITY

Sending emails purporting to be from

reputable companies to induce people to

reveal personal information.

Protect with: anti-spam filters and staff training

to spot phishing emails.

1.6 SYSTEM SECURITY

People as a weak point

(Social engineering)

1.6 SYSTEM SECURITY

Most vulnerabilities are caused by humans.

Not locking computers.

Using insecure passwords.

Not following/poor company network policies.

Not installing protection software.

Not being vigilant with email/files received.

Not encrypting sensitive data.

1.6 SYSTEM SECURITY

Brute force attack

1.6 SYSTEM SECURITY

A trial and error method of attempting

passwords. Automated software is used to

generate a large number of guesses.

Protect with: progressive lock out after 3

attempts, delays (try again in 1 hour) and

strong passwords.

1.6 SYSTEM SECURITY

Denial of service attack

1.6 SYSTEM SECURITY

Flooding a server with so much traffic it is

unable to process legitimate requests.

Protect with a firewall and detect with network

forensics.

1.6 SYSTEM SECURITY

Data interception and theft

1.6 SYSTEM SECURITY

Stealing computer-based information.

Protect with: encryption, virtual network and

staff training. Detect with network forensics.

1.6 SYSTEM SECURITY

SQL injection

1.6 SYSTEM SECURITY

A hacking technique used to view or change

data in a database by inserting SQL code

instead of data into a text box on a form.

Protect with: validation rules, database

permissions and parameter queries.

1.6 SYSTEM SECURITY

The purpose of systems software

1.7 SYSTEMS SOFTWARE

Provide a platform to run programs and to

maintain the computer system.

The purpose of an operating system

Provide a user interface.

Memory management.

Peripheral management with drivers.

Manage user files.

Manage user login and settings.

Types of user interface

Graphical: easy to use, visual and intuitive.

Command line: text based, less resource

heavy, automate processes with scripts, used

by network administrators.

Menu: single option chosen at each stage.

Natural language: speech input. Not always

reliable.

Multi-tasking

Memory management

Running more than one application at a time

by giving each one a slice of processor time.

Using virtual memory on the hard disk when

there is not enough physical RAM. Transferring

instructions and data into memory when

needed and to the hard disk when not.

Driver

Translates commands from the operating

system into hardware specific commands that

a device understands.

E.g. A printer driver tells the printer how to

print a document from the operating system.

User management

Operating system provides for:

Allowing different people to log into the same

computer with a username and password.

Remembering personal settings.

Managing access rights to files.

File management

Operating system provides:

Access permissions for files (read and write).

Opening files in associated programs.

Moving, deleting and renaming files.

Presenting a folder structure to the user.

Encryption software

Turns plaintext data into unreadable ciphertext

data using a key.

Protects data from being read by hackers.

Defragmentation

Different sized files saved on disk are deleted

over time creating gaps on the disk. New files

fill up the gaps, but may need more space than

the gap provides resulting in fragments of the

file being spread across the disk.

Defragmentation rearranges parts of files back

to contiguous space. Makes access quicker.

Compression

Reduces the size of a file.

Takes up less disk space.

Quicker to download over the internet.

Compressed files must be extracted before

they can be read.

Full backup

Every file is copied to an alternative storage

device. E.g. portable hard drive.

Files can be recovered if it is deleted or

corrupted.

Can be slow to copy large numbers of files.

Incremental backup

Only the files that have changed since the last

backup are copied.

Files can be recovered if it is deleted or

corrupted.

Much quicker than a full backup.

Ethical issues

1.8 ETHICAL, LEGAL, CULTURAL & ENVIRONMENTAL

Remember some general key points:

Losing/changing jobs.

Efficiency: robots work 24/7.

Access to IT is not equal (digital divide).

Invasion of privacy.

Responsibility for content on the internet.

Cultural issues

Censorship to prevent political unrest and

preserve culture.

Geography & economy of a country affects

access to networks and power.

Increased mobile technology impacts on how

people communicate: cyberbullying.

Environmental issues

Manufacturing computers uses fossil fuels.

Limited number of natural resources.

Data centres use 2% of global energy.

Computers contain hazardous materials, often

shipped to other countries for disposal.

Privacy issues

Increase in always on, voice activated devices

in the home.

Rise in CCTV.

Rise in social networking and GPS tracking.

Stakeholder

Anyone with an interest in a business.

Consider commenting on:

Company owners: profits & reputation.

Workers: jobs & salary.

Customers: price & convenience.

Suppliers: costs.

Local community: environment & jobs.

Open source software

Users can modify and distribute the software.

Can be installed on any number of computers.

Support provided by the community.

Users have access to the source code.

May not be fully tested.

Proprietary software

Users cannot modify the software.

Copyright protected.

Usually paid for.

Licensed per user or per computer.

Support provided by developers.

Users do not have access to the source code.

Fully tested and supported by developers.

Data Protection Act 1998

Has been replaced by

General Data Protection Regulation 2016

Data Protection Act 2018

Data should be:

Processed for the purpose clearly stated.

Relevant and not excessive.

Accurate and up-to-date.

Kept only for as long as necessary.

Secure.

Held in countries only agreed by the ICO.

Data Protection Regulation

Your rights

Right to access data.

Right to have data corrected.

Right to data erasure (to be forgotten).

Right to restrict processing.

Right not to be used for marketing.

Computer Misuse Act 1990

It is illegal to:

Make any unauthorised access to data;

with the intent to commit further offences;

with the intent to modify data, e.g. viruses.

It is illegal to:

Copy, modify or distribute software: music,

video or other intellectual property without

permission of the author.

Creative Commons Licensing

A way to grant copyright permissions to

creative work.

It allows an author to retain copyright while

allowing others to copy, distribute, and make

some uses of their work.

Freedom of Information Act 2000

Members of the public can request information

from public bodies about their activities.

Public authorities are obliged to publish data

about their activities when asked.

craig’n’dave ocr gcse computer science terminology unit 1 · memory in the processor providing...

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