Computer Science GCSE

2D and 3D Cutters

3D cutters can recognise objects in x, y, z direction 3D laser cutters can cut; glass, crystal, metal, wood

Three-dimensional Scanners

3D scanners can scan solid objects and produce a three- dimensional image Scanners take images at several points, x, y and z (lasers, magnetic, white light) The scanned images can be used in Computer Aided Design (CAD) or to a 3D printer to produce a working model

Firewall

A firewall sits between the user's computer and an external network (internet) and filter information in and out of the computer Tasks carried out by firewall: o Examining 'traffic' o Checking weather incoming or outgoing data meets criteria o If data fails the criteria, the firewall blocks 'traffic' o Firewall can keep a list of all undesirable IP addresses o Helping to prevent viruses or hackers entering the user's computer

Denial of Service Attacks (DoS)

An attempt at preventing users from accessing part of a network Usually temporary but may be damaging Attacker me be able to prevent user from: o Accessing their emails o Accessing websites o Accessing online services

Keyboards

Connected to computer with a USB connection or by wireless connection Each character has an ASCII value and is converted into a digital signal Slow method Prone to errors

Pharming

Malicious code installed on a user's hard drive or on the web server, code will redirect the user to a fake website Effect: o Creator of malicious code can gain personal data; bank account o Can lead to fraud or identity theft To remove risk: o Some anti-spyware can identify and remove pharming code from hard drive o User should be alert

Checksum

Checksum is another way to see if data has been transmitted correctly Data is sent in blocks and an additional value sent at the end of the block

Internet Service Protocol

These are companies that provide user with access to the internet

Compiler

Translates a program written in high-level language into machine code Used without compiler Executable file of machine code produced One high-level language translated into several machine code instructions Used for general use Provides an executable file

Encryption

Used to protect data in case it has been hacked Doesn't prevent hacking, makes data meaningless Need a key to decrypt the text

Cookies

A packet of information sent by a web server to a web browser Generated each time the user visits the website Every time a user visits a website, cookies will have collected some key information about the user They are able to carry out user tracking and maintain user preferences Cookies are pieces of data Information gathered by cookies doesn't contain personal information

Translators

A program must be translated into binary before a computer can use it Types of translators; Compiler, Interpreter and Assembler

Symmetric Encryption

A secret key which can be a combination of characters If this key is applied to a message, its contents is changed One key is needed to encrypt a message and another key is needed to decrypt a message Increasing the length of the key increases the strength of the encryption

Ethics

A set of principles set out to regulate the use of computers Plagiarism is when a person takes another person's idea/work and claims it as their own

Freeware

A software a user can download from the internet free of charge Once it has been downloaded, there are no fees associated (e.g. Adobe, Skype) Subject to all copyright laws User is not allowed to study, modify code

Computer Architecture

Address bus - unidirectional Data bus - bi-directional Control bus - unidirectional and bi-directional

Shareware

All the features of the full version of software are not made available; full version needs to be purchased first Subject to all copyright laws Permission needs to be obtained before software is copied and given to friends or family

Authentication

Authentication is used to verify that data come from a trusted source Works with encryption to strengthen internet security Passwords: usually a user id/name and password are used to log on to systems Digital Signatures: public key encryption; ensure an electronic document is authentic Biometrics: relies on the unique characteristics of human beings (fingerprint scans, retina scans)

Digital Cameras

Controlled by microprocessor which automatically adjusts the shutter speed, focus the image, etc. Photo is captured when light passes through the lens onto a light sensitive cell Cell is made up of pixels Number of pixels determines size of the file

Phishing

Creator sends out a legitimate-looking email; as soon as recipient clicks on link, user is sent to a fake website Effect: o Creator of email can gain personal data; bank account o Can lead to fraud To remove risk: o Many ISPs filter out phishing emails o User should be cautious

Hard Disk Drives (HDD)

Data is stored in a digital format on the magnetic surface of the disks (platter) Number of read/write heads can access all of the surfaces of the disk Each platter will have two surfaces which can be used to store the data Data is stored on the surfaces in sectors and tracks HDD have very slow data access compared to RAM

Sensors

Devices which read or measure physical properties Data needs to be converted to digital Analogue to Digital Converter (ADC) converts physical values into digital

Web addresses

Each character on the keyboard has its own ASCII code Can be represented using hexadecimal or decimal values Hexadecimal addresses are used in the address of files or webpages as a security figure Takes longer to type in URL but advantage is that you are unlikely to fall into the trap of copying a fake website

Internet Protocol (IP) Address

Each device on the internet is given a unique address known as the IP address 32-bit number written in the form: 109.108.158.1 IP address gives the location of a device on the internet whereas the MAC address identifies the device connected to the internet IP address changes, MAC address remains unchanged

High-Level Languages

Easier to read and understand as the language is closer to human language Easier to write in shorter time Easier to debug at the development stage Easier to maintain once in use

interpreter

Executes a high-language program a statement at a time No executable file of machine code produced One high-level language program statement may require several machine code instructions to be executed Cannot be used without interpreter Used when program is being developed

Random Access Memory (RAM)

Features of RAM o Volatile (contents lost if RAM is turned off) o Used to store; data, files o It can be written to or read from and the contents from the memory can be changed Larger the size of the RAM, faster the computer will operate RAM never runs out of memory, continues to run slow As RAM becomes full, the processor has to continually access the hard drive to overwrite old data on RAM with new data

Transport Layer Security (TLS)

Form of protocol that ensures the security and privacy of data between devices and users when communicating over the internet Designed to provide encryption, authentication and data integrity in a more effective way than SSL Possible to extend TLS by adding new authentication methods

Joint Photographic Experts Group (JPEG)

JPEG is a file formats used to reduce photographic file sizes Reducing picture resolution is changing the number of pixels per centimetre When photographic file undergoes compression, file size is reduced JPEG will reduce the raw bitmap image by a factor between 5 and 15

CD/DVD Disks

Laser (red) light is used to read and write data in the surface of the disk Use a thin layer of metal alloy to store data Interpreter Both systems use a single, spiral track which runs from the centre of the disk to the edge DVD uses Dual-Layering which increases the storage capacity (two individual recoding layers)

Control of Street Lighting

Light sensor sends data to the ADC Digitises data and sent to the microprocessor Microprocessor samples data every minute If data from sensor < value stored in memory: o Signal sent from microprocessor to street lamp o Lamp switched on

Media Access Control (MAC)

MAC address refers to a number which uniquely identifies a device on the internet Refers to the network interface card (NIC) which is part of the device Usually made up of 48 bits shown as six groups of hexadecimal digits NN:NN:NN:DD:DD:DD o (NN:NN:NN) first half is the identity number of the manufacturer of the device o (DD:DD:DD) second half is the serial number of the device Types of MAC Address: o Universally Administrated MAC Address (UAA) o Locally Administrated MAC Address (LAA) o UAA is the most common type set by the manufacturer Reasons to change MAC address using LAA o To ensure they follow the correct formula o To bypass MAC address filter on a router or a firewall o To get past certain types of network restrictions

Application of 2D Scanners at an Airport

Make use of (OCR) to produce digital images which represent the passport pages Text can be stored in ASCII format The 2D photograph in the passport is also scanned and stored as jpeg image The passenger's face is also photographed using a digital camera and compared using face recognition software Key parts of the face are compared (distance between eyes, width of nose)

Pointing devices

Mouse/trackball o Traditional; mechanical ball, connected by USB port Modern type; red LEDs to detect movement

Security

Need to keep data safe from accidental damage, including corruption and human errors Need to keep data safe from malicious actions, including unauthorised viewing, deleting, copying and corruption

Solid-State Storage (SSD)

No moving parts and all data is received at the same time (not like HDD) Store data by controlling the movement of electrons within NAND chips, as 1s and 0s Non-volatile rewritable memory Benefits of using SSD rather than HDD: o More reliable (no moving parts) o Considerably lighter (suitable for laptops) o Lower power consumption o Data access if faster than HDD o Very thin o Run much cooler than HDDs Drawback - questionable longevity (20GB per day

LCD Projectors

Older technology than DLP A powerful beam of white light is generated from a bulb This beam of light is then sent to a group of chromatic-coated mirrors; these reflect the light back at different wavelengths When the white light hits the mirrors, the reflected light has wavelengths corresponding to red, green and blue These three different light pass through three LCD screens; these screens show the image to be projected as millions of pixels in grayscale When the coloured light passes through the LCD screens, a red, green and blue version of the grey image emerges Finally, the image passes through the projector lens onto the screen

Viruses

Program that can replicate itself with the intention of deleting or corrupting files, cause computer malfunction Effect: o Can cause computer to crash o Can delete or corrupt files/data To remove risk: o Install anti-virus software o Don't use software from unknown sources o Be careful when opening emails from unknown

Low-Level Languages

Refer to machine code Binary instructions that computer understands

Free Software

Software source code can be freely accessed and modified as required Run, copy, change or adapt free software (e.g. Scribus, Abiword) Possible to distribute modified versions of software to friends and family

Spyware

Software that gathers info by monitoring key presses on the user's keyboard and info is sent back Effects: o Access to all data entered o Software is able to install other spyware, read cookie data To remove risk: o Use of anti-spyware software o Use a mouse to select characters from passwords rather than typing them

Loudspeakers/Headphones

Sound is produced by passing the digital data through a DAC then through amplifier and then emerges from loudspeaker Produced by voltage differences vibrating a cone in the speaker at different frequencies

Musical Instrument Digital Format (MIDI)

Storage of music files Communications protocol that allows electronic musical instruments to interact with each other Stored as a series of demands but no actual music notes Uses 8-bit serial transmission (asynchronous) Each MIDI command has a sequence of bytes: o First byte is the status byte - informs the MIDI device what function to preform o Encoded in the status byte is the MIDI channel (operates on 16 different channels) Examples of MIDI commands: o Note on/off: indicates that a key has been pressed o Key pressure: indicates how hard it has been pressed (loudness of music) Needs a lot of memory storage

Hacking

The act of gaining illegal access to a computer system Effect: o Leads to identity theft, gaining personal information o Data can be deleted, changed or corrupted To remove risk: o Firewalls o Strong passwords/ user IDs o Use of anti-hacking software Difference between hacking and cracking o Hacking breaks into computer system to steal data o Cracking is where someone edits a program code, malicious

Wardriving

The act of locating and using wireless internet connections illegally Effects: o Possible to steal internet time o Possible to hack into wireless network and steal user's password To remove risk: o Use complex passwords o Firewalls

MP4

This format allows the storage of multimedia files rather than just sound Music, videos, photos and animations can be stored Videos, could be streamed without losing any real discernible quality

Assembler

Translates a low-level language program into machine code Executable file of machine code produced One low-level language translated into one machine code instructions Can be used without assembler Used for general use

Light projectors

Two common types of light projectors: o Digital Light Projector (DLP) o LCD Projector Projectors are used to project computer output onto larger screens/interactive whiteboards

Secure Sockets Layer (SSL)

Type of protocol that allows data to be sent and received securely over the internet When a user logs onto a website, SSL encrypts the data https or padlock in the status bar When user wants to access a secure website: o User's web browser sends a message so it can connect with required website which is secured by SSL o Web browser requests that the web server identifies itself o Web server responds by sending a copy of its SSL certificate o Web browser checks if certificate is authentic o Sends signal back to web browser o Starts to transmit data once connection is established o If not secure, browser will display an open padlock

Universal Serial Bus (USB)

USB is an asynchronous serial data transmission method USB consists of: o Four-wire shielded cable o Two wires used for power and earth o Two wires used in data transmission Advantages Automatically detected Only fit one way, prevents incorrect connections Different transmission rates Disadvantages Maximum cable length is about 5 metres Transmission rate is less than 500 mb/sec

3D Printers

Used for models of cars Produce solid objects that work Built up layer by layer, using powdered resin, ceramic powder A design is made using Computer-aided Design (CAD)

Microphones

Used to input sound to a computer When a microphone picks up sound, a diaphragm vibrates producing an electric signal The signal goes to a sound card and is converted into digital values and stored in computer Voice recognition, voice is detected and converted into digital

Laser Printers

Used to print flyers, high quality Use dry powder ink (toner) and static electricity to produce text and images Prints the whole page in one go 1. (steps 1-4 same as inkjet) 2. Printing drum is given a positive charge; as the drum rotates, a laser beam is scanned across it removing the positive charge leaves negatively charged areas which match the text/image 3. Drum is then coated with positively charged toner, it only sticks to negatively charged parts of the drum 4. A negatively charged sheet is rolled over the drum 5. Toner on the drum now sticks to the paper to produce copy of page 6. Paper finally goes through a fuser (set of heated rollers); heat melts the ink so it is permanent 7. Discharge lamp removes all electric charge from the drum, ready to print next page

Inkjet Printers

Used to print one-off pictures and documents 1. Data from document sent to printer driver 2. Printer driver ensures data is in correct format 3. Check made by printer driver that chosen printer is available 4. Data is sent to printer, stored in a temporary memory (printer buffer) 5. Sheet of paper is fed; sensor detects if paper is available in paper tray 6. Print head moves across paper printing text/image, four ink colours sprayed in exact amount 7. Paper is advanced so next line is printed 8. Repeated until buffer is empty 9. Once it is done, printer send an interrupt to the processor (request for more data to be sent)

HTML (HyperText Mark-up Language)

Used when writing and developing pages Mark-up language is used in the processing Html use <tags> to bracket piece of codes Different intensity of colours is determined by its hexadecimal value

Blu-ray Disks

Uses blue laser to carry out read and write operations Wavelength of laser light is less than CD and DVD (stores up to five times more data than DVD) Automatically come with secure encryption (prevent piracy and copyright infringement) Used as back-up systems

Digital Light Projectors (DLP)

Uses millions of micro mirrors the number of micro mirrors and the way they are arranged on the DLP chip determines the resolution of the image When the micro mirrors tilt towards the light source they are on When the micro mirrors tilt away from the light source they are off This creates a light or dark pixel on the projection screen A bright white light source passes through a colour filter on its way to the DLP chip White light splits into primary colours

MP3

Uses technology known as Audio Compression to convert music and other sounds into an MP3 file format This compression reduces the normal file size by 90% o Done using file compression algorithms which use Perceptual Music Shaping o Removes sounds that human ear cannot hear properly o Certain sounds are removed without affecting the quality too much CD files are converted using File Compression Software Use lossy format as the original file is lost following the compression algorithm

USB Flash Memories

Very small, lightweight suitable from transferring files Small back-up devices for photo, music Solid state so need to be treated with care

Syntax Errors

When program is being compiled, if any syntax errors are found no translated program is produced Instead, a list of all errors in program is produced Programmer corrects program and recompiles When a program is being interpreted, the interpreter preforms the action until syntax error is found The programmer is the alerted to the place in the program where error was found The error is corrected and interpretation continues

Converting into digital photos

- Image is converted from analogue to digital (using ADC) - Image is turned into pixels - Each pixel is given a binary value - Pixels form a grid (to create the image) - Each pixel has a colour

Lossy File Compression

- Lossy reduces the file size more (than lossless) - The redundant data can be removed from the files - Files can be sent quicker

The Fetch-Execute Cycle

- Program counter (PC) holds address / location of the instruction - The address held in PC is sent to MAR - Address is sent using address bus - PC is incremented - The instruction is sent from address in memory to MDR - Instruction is transferred using the data bus - Instruction sent to CIR

Internet Service Provider (ISP)

- Provide access to the internet - Give users an IP address - Supports domain names - Provide security services - Provide web hosting facilities - Provide access to Email / Mailbox - Provides online data storage

Units for Computer memories

A binary digit - BIT, 8 bits = 1 byte Byte is used to measure memory size

Synchronous data transmission

A continuous stream of data (not in discrete groups like asynchronous): o Ensures that the sender and receiver are synchronised with each other o Faster method

Optical Character Recognition (OCR)

A software which converts scanned documents into a text file format

Automatic Repeat Request (ARQ)

ARQ is another method to check if data has been transmitted correctly It uses and acknowledgement (message sent by the receiver indicating that data has been received correctly)

Error-Checking

ARQ, Checksum, Echo check, Parity Checking

Transmission of Data

Asynchronous data transmission Synchronous data transmission

Half-duplex data transmission

Both directions but not at the same time (e.g. phone conversation where only one person speaks)

Full-duplex data transmission

Both directions simultaneously (e.g. broadband connection on phone line)

Touchscreens

Capacitive (medium cost tech) - An electrostatic/electric field is created - Sensor(s) (around the screen) monitor the electrostatic field - When touched (electrostatic) charge is transferred to finger - Location of touch is calculated // Co-ordinates used to calculate touch Disadvantages Gloves are an insulator The charge can be blocked from finger - use capacitive gloves: this will allow the charge to be charged/disturbed Infra-red heat (expensive) o Use glass as the screen material o Needs warm object to carry an input operation Infra-red optical (expensive) − Rays are sent across screen − Has sensors around edge − Ray is broken by a finger − Calculation is made to locate the 'touch' Resistive (inexpensive) Uses multiple layers When top layer is touched, two layers make contact Circuit is completed when the layers touch Point of contact is calculated Resistant to weather Less chance of input error Does not require a mouse or keyboard

Hexadecimal

Closely related to the binary system Hexadecimal is a base 16 system Numbers 0 to 9 and letters A to Fare used to represent each hexadecimal digit

Cypher Text

Cypher text is the output from an encryption algorithm

Asynchronous data transmission

Data being transmitted in an agreed bit pattern: o Data bits are grouped together & sent with control bits o This means the receiver of the data knows when the data starts and ends, prevents data getting mixed up

Uses of hexadecimal

Defining colours in Hypertext Markup Language (HTML) Media Access Control (MAC) addresses Assembly languages and machine code Debugging Memory Dumps Hexadecimal is used when developing new software or when trying to trace errors Memory dump is when the memory contents are output to a printer, monitor. Assembly code and machine code (low level languages) Computer memory is machine code/ assembly code Using hexadecimal makes it easier, faster, less error prone to write code compared to binary. Using machine code (binary) takes a long time to key in values and prone to errors

Read Only Memory (ROM)

Features of ROM: o Non-volatile (contents remain even when ROM is turned off) o Used to store start up instruction (basic input/output systems) o Data/contents of a ROM chip can only be read, cannot be changed

LCD and LED Monitors

Front layer of monitor is made up of Liquid Crystal Display (LCD), these tiny diodes are grouped together in threes as pixels (LCD doesn't emit any light) LCD monitors are back lit using Light Emitting Diode (LED) because: o LEDs reach their maximum brightness immediately o LEDs sharpens image (higher resolution), CCFL has yellow tint o LEDs improve colour image o Monitors using LED are much thinner than CCFL o LEDs consume very little power Before LEDs, LCD monitors were backlit using CCFL CCFL uses two fluorescent tubes behind the LCD screen which supplies the light source

Plain text

Is the normal representation of data before it goes through an encryption algorithm

Quick Response (QR) Codes

Made up of a matrix of filled in dark squares on a light background Can hold more storage (7000 digits) Read/scanned using app The app/device processes the image Each small square/pixel is converted to a binary value Advantages of QR codes: o No need for the user to write down website address o QR codes can store website addresses

Simplex data transmission

One direction only (e.g. computer to printer)

Parity Checking

Parity checking is used to check weather data has been changed or corrupted following transmission from one device to another A byte of data is allocated a parity bit Systems that use even parity have an even number of 1-bits Systems that use odd parity have an even number of 1-bits

Proxy server

Proxy servers act as an intermediary between the user and a web server Functions of proxy servers: − Prevents direct access to the webserver − If an attack is launched it hits the proxy server instead − Used to direct invalid traffic away from the webserver − Filters traffic

Binary Systems

The binary system is based on the number 2 Made up of 1s and 0s Use of binary numbers in computer systems

Control Unit

The control unit controls the operation of the memory, processor and input/output devices

Processor

The processor contains the Arithmetic and Logic Unit (ALU)

Actuators

Used in many control applications involving sensors and devices (ADC and DAC)

Two-dimensional Scanners

Used to input hard-copy documents The image is converted into an electronic form which can be stored in the computer o Document is placed on a glass panel o A bright light illuminates the document o A scan head moves across the document until the whole page is scanned. And image of the document is produced and sent to a lens using a series of mirrors o The lens focuses the document image o The focused image now falls onto a charge couple device (CCD) which consists of a numbers of integrated circuits o Software produces a digital image from the electronic form If the original document was a photo/image, then the scanned image forms an image file such as JPEG

Serial data transmission

When data is sent one bit at a time over a single wire: o Works well over long distances o Data transmitted at a slower rate (USB)

Echo check

When data is sent to another device, this data is sent back again to the sender The sender compares the two sets to check if any errors occurred Not reliable

Parallel data transmission

When data several bits (1 byte) are sent down several wires at the same time o Works well over short distance o Faster method (internal components use parallel for high speed)

Ways bank protect their costumers

o Banks use 10/12-digit code unique to the costumer o May be asked to input three random numbers from a four-digit PIN o Some use a hand-held device into which a customer inserts their card. Device will generate an eight-digit code which the customer types into web page o Some ask to key in parts of their passwords using drop-down boxes (using a mouse)

Barcode readers/scanners

− Shines light laser at barcode − Light is called an illuminator − Light is reflected back − Sensors detect the light Advantages − barcode can identify a product − barcode can be used to look up product − data about stock levels can be stored on a system

Lossless File Compression

− The file can be restored to the original state − Lossy would remove data − Value is recorded in an index