9618 Exam: Data Representation

• Concise notes from mark schemes for the 9618 exam
• Paper 1

Information Representation

• The section covers data representation, multimedia, and compression techniques.

Data Representation

• Data representation focuses on different ways to represent data in computers.
• The section covers BCD, hexadecimal, ASCII, and Unicode.

Benefits of BCD

• BCD is more straightforward to convert between BCD and denary.
• BCD is less complex to encode and decode, which simplifies programming tasks.
• BCD makes it easier for digital equipment to display information in a human-readable format.
• BCD can represent monetary values exactly.

Applications of BCD

• Electronic displays, like calculators and digital clocks, use BCD to show individual digits.
• BCD simplifies the conversion between denary and BCD.
• BCD is used in the BIOS of PCs for storing date and time, as it is easier to convert with denary.

Applications of Hexadecimal

• MAC addresses use hexadecimal.
• HTML color codes are represented in hexadecimal.
• Memory addresses in assembly language and machine code can be referred to using hexadecimal.

ASCII Representation

• Each character is assigned a unique code in ASCII.
• The character is replaced by its unique code for storage and processing.
• Codes are stored in the same order as the characters in the word.

Character Set

• A character set is a defined list of characters recognized by the computer (e.g., ASCII, UNICODE, Extended ASCII).
• Each character that the computer can represent has a unique corresponding binary number.

Similarities (ASCII, UNICODE, Extended ASCII)

• All can use 8 bits.
• ASCII is a subset of Unicode.
• Each represents characters using a unique code.

Differences (ASCII, UNICODE, Extended ASCII)

• Unicode can represent multiple languages and a wider range of characters than ASCII.
• ASCII uses 7 bits, Extended ASCII uses 8 bits, and UNICODE uses 16 bits.

Multimedia

• The section covers bitmap graphics, vector graphics, and sound.

Bitmap Graphic

• Bitmap graphics are made up of pixels, each assigned a single color with a unique binary value.
• Bitmap graphics are stored as a binary number sequence, storing the binary value of each pixel.
• Enlarging bitmap images can lead to pixelation.
• Bitmap images tend to have larger file sizes due to the storage of data for each pixel.
• Bitmap images can be significantly compressed.
• Editing a bitmap image can be more difficult.

Pixel

• A pixel is the smallest addressable element in an image.

File Header

• A file header stores metadata about the bitmap image, such as color depth and image resolution.
• The file header can specify file type, compression type, dimensions (width x height), and file size.

Image Resolution

• Image resolution is the total number of pixels in an image, calculated as the number of pixels wide multiplied by the number of pixels high.
• Increasing the resolution allows more pixels to be stored.
• Higher resolution images are sharper and less pixelated.

Bit Depth/Colour Depth

• Bit depth is the number of bits used to represent each color (number of bits per pixel).
• The number of colors that can be represented in an image depends on the bit depth.
• Increasing the bit depth allows a greater range of colors, resulting in an image closer to the original, but leads to increased file size.

Vector Graphic

• Vector graphics store a set of instructions on how to draw the shape.
• Vector graphics do not pixelate when scaled or enlarged.
• Individual components of a vector image can be edited.
• Vector graphics tend to have smaller file sizes as they contain instructions rather than pixel data.
• Vector graphics do not compress well, resulting in little redundant data.

Drawing Object

• Drawing objects are components of a vector graphic created using a formula/command.

Drawing Property

• Drawing properties are data about the shapes and define the appearance of a drawing object.

Drawing List

• A drawing list is a list of the shapes that make up an image, or a list of all drawing objects in an image.
• Stored commands are required to draw each object.

Vector Graphic Representation

• Vector graphics are encoded as a series of geometric shapes.
• The coordinates of drawing objects are stored in an image.
• A drawing list contains commands for creating each individual object and its attributes.

Sound Representation

• Sound is represented by recording amplitude a set number of times in a second.
• Each amplitude is given a corresponding unique binary value/number.
• The binary number is saved/stored in sequence.

Sampling

• Sampling involves taking measurements at regular intervals and storing the values.

Sampling Rate

• Sampling rate is the number of samples taken per unit of time (per second).

Effect of Increasing Sampling Rate

• Sound is recorded more often, resulting in smaller gaps in the sound wave and between samples.
• Increasing sampling rate reduces quantization errors.
• Increasing sampling rate improves accuracy because the digital waveform more closely resembles the analog waveform.
• Increasing sampling rate increases the file size, because doing so increases the number of samples taken and therefore requires bits.

Sampling Resolution

• Sampling resolution involves the number of bits used to store each sample.

Effect of Increasing Sampling Resolution

• Increasing the number of bits used to store each sample allows more bits per sample.
• Higher resolution allows a wider range of amplitudes to be stored.
• Increasing resolution increases file size.
• The digital waveform is closer to the original (improves accuracy).
• Smaller quantization errors occur.

Analogue data

• Analogue data is a variable or data value that is constantly changing.

Compression

• Compression is the the process of reducing file sizes

Compression Reasons

• Reduces file size, taking up less space in memory, allowing space for other files to be stored.
• Enables faster download and upload rates, reducing transmission time from/to the web.
• Reduces bandwidth used to download/transmit.
• The original file might be too large to send through email, e.g., as an attachment.

Lossy Compression

• Lossy compression results in original data being lost or deleted (cannot be done in a text file), and the file cannot be reconstructed.
• If used on a text file, it would corrupt the contents, since all data is required.
• Videos have a lower resolution, so buffering will be reduced when streamed.

Lossless Compression

• In lossless compression, original data is preserved.
• Lossless compression is used when all data is needed, such as when a file needs to be fully restored, a high quality video/image is needed, or the file is already relatively small.

Compressing Files - Sound

• The amplitude range is reduced to only the range used, reducing the bits needed to store each sample.
• Run-length encoding (RLE) groups consecutive sounds, providing the binary value of sound recorded along with the number of repeats.
• Record only the changes in sound (not the actual sounds).
• Consecutive sounds with the same binary value are grouped along with the number of repeats.

Compressing Files - Images (Lossy)

• Reduce bit depth to reduce the number of bits used to store a color.
• Reduce the number of colors to require fewer bits to store each color.
• Reduce resolution to lower the number of pixels altogether.

Compressing Files - Images (Lossless)

• RLE replaces sequences of the same color pixel with the color code and the number of identical pixels.

Run-length Encoding

• Run-length encoding identifies groups/sequences of repeated characters, replacing them with a copy of the character and the number of times it occurred.

RLE Limitations

• RLE works by storing a color and the number of times it occurs consecutively.

Communication

• This section covers communication networks including the internet

Networks including the internet

• Covers LAN, WAN, Client-Server Model, Topologies, Cloud Computing, Wired vs Wireless etc.

LAN - Local Area Network

• A LAN allows communication and sharing of data between devices on the network.
• Resources like hardware and software can be shared.
• A LAN enables central management of security, backup, etc.
• It covers a small geographical area, and the connection between devices is usually physical.
• The infrastructure is privately owned and not controlled by external organizations.
• LANs have high data transfer rates.
• Protection is easier to implement, making LANs more secure than WANs.

WAN - Wide Area Network

• A WAN covers a large geographical area, and the connection is often virtual.
• WANs have a low data transfer rate.
• WAN can have private or public ownership and is generally controlled by external organizations.

Client-Server Model

• Web pages and data are saved on servers.
• The client sends a request to the server.
• Web servers process requests, perform tasks, and return results to the client.
• The client displays the results to the user.
• The user's computer is the client.
• A server can host shared files.
• Users can request a file from any client computer.
• Files can be accessed simultaneously by several users.

Client-Server Model Examples

• Sending and receiving an email.
• Using a print or file server.
• A company/school storing files centrally.

Peer-to-peer network Features

• Computers are of equal status.
• Each computer provides access to data and resources.
• Computers can communicate and share resources.
• Each computer is responsible for its own security.

Peer-to-peer network Drawbacks

• Reduced security occurs because there is no central management of security, which leaves each computer at risk of viruses from other computers.
• Lack of central management of back-up makes any computer that is not backed up at risk of total lost data.
• There is no central management of files, making it hard to maintain consistency.
• Computers have slower response times because they are accessed by other computers.
• Files may not always be available, because not all computers will be switched on.

Thick-Client

• Server performs minimal processing for client.
• Most resources are installed locally, and clients do most of their processing independently.

Thin-Client

• The server performs all processes required by task/data storage.
• Clients only send requests to the server and display returned results.

Star Topology

• Devices are only connected to central router (switch/hub).
• Each computer is only connected to the server.
• There are fewer collisions, resulting in high performance, as each device is only connected to the switch.
• It's easily scalable.
• It's more resilient because it is not reliant on one cable.

How Data Is Transmitted

• Data from the sending device is transmitted to the router.
• The data has the address of the recipient.
• A router determines the recipient's destination address using a routing table.
• The router transmits data directly and only to the recipient.

Mesh Topology

• All computers are connected to at least one other device.
• There are multiple routes between devices.
• Computers can act as relays and forward packets to the final destination.

Advantages of Mesh Topology

• If one line goes down, alternate routes are available.
• The improved security is related to not using one main line.
• Fewer collisions occur.
• New nodes can be added without interfering with other nodes.

Cloud Computing

• Cloud computing refers to accessing a file/service on a remote server.

Public Cloud

• Consists of services offered by a third party over the public internet.
• The services are available to anyone with appropriate software/equipment.

Private Cloud

• Private cloud services consist of services offered by a private internal network.
• The services are only available to the select users and the dedicated system is only accessible from the organisation.

Advantages of Cloud Computing

• It's can be free.
• Storage is saved on existing devices.
• Data can be accessed from any device with internet access.
• Data will likely be backed up and there is a higher chance for recovery.
• Provides better security.
• Scalable and easy to share.

Disadvantages of Cloud Computing

• It's only accessible with internet access.
• It can take a long time to upload/download the data.
• It can be expensive.
• There may be limited storage space for free.
• There may not be backup/recovery or security options.
• You are reliant on someone else/dependant on a third party for security or backup.
• You can't access file if the server goes down.

Disadvantages of a Public Cloud

• A loss of control occurs because data is stored on remote infrastructure, and the user relies on an external provider.
• It requires a reliable internet connection to access data.
• There are increased recurring costs because provides charger must be paid and LAN is one-time only.

Advantages of a Wired Network

• Higher bandwidth, leading to less latency.
• Stable connection makes it less vulnerable to external interference.
• The network is more secure and confidential data can be transferred more securely.

Advantages of a Wireless Network

• Wireless networks free the user from a single location, so devices can be potable.
• Physical connection is not needed.
• They are easily expandable and scalable if more devices want to join.
• Wireless networks have low cabling needs and so are cheaper for setup.
• They allow access in remote locations.

Disadvantages of a Wireless Network

• Higher latency
• Is is affected by weather
• Slower transmission speed
• Direct line of sight needed

Copper Cables

• Data is transmitted through electrical signals.

• Lower transmission rate

• Chance of interference and interception

• Fibre-optic cables and radio waves are another form of communication network

Fibre-optic Cables

• Data is transmitted using light.
• Has a greater bandwidth and faster transmission speed
• Has a smaller risk of interference.
• Can be used over long distances needing less signal boosting
• more difficult to hack into

Wireless communication

• carries data wirelessly in the form of electromagnetic waves

Satellite

• a communication device in Earth's orbit
• receives and transmits data

Switch

• allows communication between devices
• connects individual devices to each other
• receives transmissions and forwards them to their destination

Server

• manages access to a centralised resource (usually between devices on LAN)

WNIC - Wireless Network Interface Controller Functions

• provides interface/allows connection to wireless network as an antenna
• receives analogue waves and converts them to digital
• encrypts and decrypts data to allow for secure data transmission.
• provides MAC address to identify device on the network

Hardware

• Hardware provides radio communication from central device to nodes on a network,
• Allows the connection of devices using radio waves/signals/Wi-Fi.
• Allows wireless enabled devices to connect to a wired network.

Bridge

• Connects two LANs with the same protocol.
• Data transmission is allowed between two networks using the same protocol.

Repeater

• Restores a digital signal so it can be transmitted over greater distances.

Role of Router:

• Receives packets from devices or the external network/internet.
• Stores IP and MAC addresses of all devices attached to it.
• Maintains a routing table.
• Routes/forwards packets to destination.
• Finds destination of a packet (using IP addresses).
• Assigns private IP addresses to devices on a LAN.
• Finds the most efficient path to the destination.
• Can act as a firewall, gateway, and perform protocol conversion/changes packet format.

Ethernet

• A protocol for data transmission over a wired network.
• Uses CSMA/CD.
• Data is transmitted in frames, each with a source and destination address and error checking data.

CSMA/CD (protocol)

• Used to detect and prevent collisions
• A device/node that listens to a communication channel (scans voltage).
• Data is only sent when the channel is free/idle meaning the line is empty.

Bit streaming

• Data is compressed before transmitting
• Video is transmitted continuously as series of bits
• On download, the server sends data to a buffer on the client computers
• The recipient receives the bit stream from the buffer

Real-time vs On-demand bit streaming

• Real-time: Used when watching a live stream, event is captured live, cannot be paused or rewound
• On-demand: Video has already been recorded, can be watched at any users convienence, can be paused and rewound

The WWW vs The internet

• WWW: Uses http/https protocol to transmit data, collection of web pages
• Internet: Uses TCP or IP protocols, interconnected network of networks

Hardware Supporting the Internet (PSTN)

• Hardware Supporting the Internet (PSTN): Consists of many different types of communication lines, allows for full duplex data transmission, communication passes through different switching centres Line remains active even during a power outage.

IPv4:

• 4 groups each represented by 8 bits (32bit)
• Either denary or hexadecimal with numbers between 0-255 (in each group)
• Separated by full stops

IPv6

• 8 groups each represented by 16 bits (128bit)
• Hexadecimal numbers between 0 and FFFF
• Groups only contains 0 can be replaced with ::
• Separated using colons
• Used when the number or IP addresses needed exceeds number available using IPv4

Subnetting benefits

• Improves security
• Allows extension of network/easier to expand
• Reduces amount of traffic in a network
• Easier maintenance and management

IP address in subnetwork

• Made up of network ID and host ID
• Each device on the subnetwork has the same network ID with different subnetwork
• Every device in each subnetwork has a different host ID but the same network ID
• Host ID uniquely identifies device within the same subnetwork

Public IP address

• Is visible to any device on the internet, is assigned to allow direct access to the internet, allocated by ISP
• Unique throughout internet

Private IP address

• Only visible to devices within the LAN, user for internal LAN communication only, allocated by router, only unique within LAN

Static vs Dynamic IP adress

• A static IPadress does not change each time a device connects to the internet
• A dynamic IP address is reallocated each time a device rejoins a network

URL, WWW and DNS Use

• URL is entered into web browser and parsed to obtain the Domain name
• The Domain name is sent to DNS, the DNS has a database of domain names with their IP addresses
• if found, the IP addresses is returned to web browser
• If not found, the request is forwarded to a higher level DNS and the IP addresses returned is added to a database

Computers and their Components

• Covers the need for storage, embedded systems, periperhals, processing

Need for Secondary Storage

• To store files, data, and software long-term.

Need for Primary Storage

• To store files needed to boot the system.
• To store the OS, or software for the system.
• To store intermediate data and current data being processed.

Embedded system

• Microprocessor within a larger system that performs a specific task
• The system has memory, input output abilities and a processor
• Integrated into machine, not easily changed by the user
• The system has a combination of hardware and software designed for a specific function
• The system doesn't have an operating system and does not require much processing power

Disadvantages of an embedded system

• Difficult to change/update the firmware or upgrade the device
• Cannot be easily adapted for another task
• Difficult to update or repair

Operation of Laser Printer

• Contains a revolving drum that is given an electrical charge.
• Contents of the page are drawn on the drum as an electrostatic charge by a laser beam that moves back and forth.
• The drum is coated with oppositely charged toner, which only sticks to areas charged by the laser beam.
• The drum then rolls over electrostatically charged paper, transferring the pattern onto the page.
• Paper is passed through a fuser/is heated to seal image.
• The electrical charge is removed from the drum, and excess toner is collected.

Operation of 3D Printer

• Addative manufacturing is used
• Digital CAD file is created
• Builds up one layer at a time from bottom using xyz coordinate
• Material is fused together layer by layer

Use of temperature sensor

• Prevents overheating ensures material is hot enough
• Identifies material of object/material being used

Microphone Operation

• Has a diaphragm
• Incomming Sound causes vibrations about the diaphragm
• This cause coil to move past a magnet resulting in the electricity being produced

Speaker

• A coil is sent to the speaker and passes through it
• Current in coil creates an electromagnetic field
• An electromagnet is repelled by or attracted based on direction of current
• Movement of coil causes the diaphragm to vibrate, the vibrates causes sound waves

Harddrive vs Solid State Memory

• Platter divisions makes the hard drive have greater unit storage over ssds
• Solids State memory (SSD) have fast data access times and no moving parts over optical drives

Operation of Solid State Memory

• Use a grid of columns and rows that has transistors at each intersection.
• transistors stores voltage to represent the 1 or 0
• Not possible to overwrite existing data (need to erase first then write data into location)

Visual Display

• Virtual headsets can change the appearance and how the player experiences the gameplay

Purpose of a data Buffer

• The data to device or external source, data is temporary stored here
• Allows the device to operate indepently each other

Distinguish the ROM and RAM

• ROM provides the the system with instruction and can stores the booting information
• RAM stores the data currently being used by the system either static or dynamic

Advantages/Disadvantages of SRAM

• Has faster access time but with low data density , has less power because does not need to be refreshed

Advantages/Disadvantages of DRAM

• Has higher data/bit density and needs to be refreshed , has higher power consumption
• Slower access speed and costs less

Control System in computer

• Uses feedback and produces an action Role of an Actuator
• Generates signal to energy which lead a action for a component

Importance of Feeback

• Ensures the the criteria that as been set

Logic Gates and Logic Circuits

• Boolean logic is the central point on the the functions of gates and circuits

CPU and it's components

• Has several components that each have their own unique function to keep the computer running correctly

Stored Program Concept

• Instructions and data are stored in the same memory space in memory

Components in Von Neumann Architecture

• Buses, registers, CPU, CU, ALU, IAS, System clock

General Purpose Registers

• Stores temporary data when performing operations, used for any purpose and can be used for instructions

Special Purpose Registers

• Hold status of a program, Specialised for specific use, can only be used by certain programs

Program Function in CPU

• Hold's the address of the next instruction to be loaded and is incremented once an instruction has been carried out

CPU functions

• Sends/receives control signals along the control bus. Manages the execution of instructions

CPU Memory functions

• Synchronises computer operations by creating time signals.
• Allows operations to be processed in the correct order / sequence.

Performance on multi-cores and singular

• Cores provides a one instruction and can be carries out simultaneously
• software may not be designed for multiple cores

Bit manipulation

• changing is the structure or binary in a regiter for various function in a computer.

Operating system

• Provides an user system and memory managant during each operation and function

Memory Management

• Controls movement of data between RAM and processor
• Allocates memory to processes
• Reclaims unuysed block of RAM

Utility software

• Helps set-up/optimise/maintain the computer

Disk - Formatter

• Prepares/initialises for storing files by partitioning it

Software to removes unnescary files

• Used for optimization with files on the memory

Software and Program library

• Program library can reduce lines of code and save a lot of time of the developer

benefits or Drawbacks of Using Compilers and Interpreters

• Interpreters are used for real time edits during testing
• Compilers produce executable, there are other benifits listed

Errors in Compilers and Interpreters

• Both will highlight a specific list of error to help the developer

Language structure/ Software Security

• Helps with various function such as adding comments , highlining key words.

System and Software

• Keeping the software up to with certain standards

Data Security

• is the protection of data against loss/corruption.