Computer Science A-level Unit 1

Binary System
Base 2 numbering system with digits 0 and 1.
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Denary System
Base 10 numbering system with digits 0-9.
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Hexadecimal System
Base 16 numbering system with digits 0-F.
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Hypertext Markup Language is a language used to develop web pages. HTML code often uses hexadecimal numbers to represent colours e.g. font colour.
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MAC Addresses
A Media Access Control Address is a number that uniquely identifies a device on a network. It is usually a 48-bit number represented as a hexadecimal.
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Assembly Code
A programming language that uses hexadecimal values.
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An integer is a positive or negative whole number. An unsigned integer can be stored as binary code. There are two systems used to represent signed integers in binary.
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Binary Coded Decimal is a system for representing single digit positive numbers. It uses 4 bits to represent each digit. It is used in e.g. calculators or digital clock displays.
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Character Code
A binary code that represents a character.
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American Standard Code for Information Interchange is an internationally agreed standard for representing characters as binary codes. Characters are represented as 7-bit codes. The most significant bit is 0.
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It is used to represent any possible text in code form including all languages in the world. The first 128 characters in Unicode are the ASCII codes.
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A Code-Point
Each character in Unicode (binary code). E.g. U+0041 is the code-point for A. 00 and 41 are the hex characters representing two bytes.
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Vector Graphic
A graphic consisting of components (objects) defined by geometric formulae and associated properties e.g. colour and style. The vector graphics file has a drawing list with a command for drawing each object defining its attributes e.g. shape, colour.
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Bitmap Graphic
An image made up of pixels which are defined by two properties: colour and position in the bitmap matrix. A bitmap file has the pixel data and a header with the image resolution and coding scheme for the pixel colour.
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The smallest picture element that can be represented.
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Colour Depth
The number of bits used per pixel. 2 to the power of the number of bits is the number of colour combinations available e.g. 4 bits = 16 colours, 8 bits = 256 colours, 32 bits = 2 million colour combinations.
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The number of pixels in a stored image or the number of pixels on a monitor/ screen. It is the number of pixels per row x the number of rows.
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Sound Waves
They are created by variations in air pressure. Sound waves form a continuous but irregular pattern where the amplitude (volume) varies.
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Analogue Data
Analogue or continuous data can have an infinite number of values e.g. as the amplitude increases from 10 to 11, the amplitude will pass through every possible value in between.
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Discrete Data
Discrete or not continuous data is what computers use. The value is either 0 or 1.
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Band Limiting Filter
A component of a sound encoder used to remove high frequency components that the ear would not be able to detect.
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Sampling Rate
The number of samples taken per second. It is the number of verticals slices on a graph. Too many samples would require the storage of lots of data. Too few samples would reduce the quality of the digital recording.
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Nyquist's Theorem
The theorem states that the optimum sampling rate occurs at a frequency at least twice the highest frequency. I.e, sampling must occur at least twice per cycle for the sound to be reproduced accurately.
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Refresh Rate
The number of times the screen can be refreshed each second. Human eyes will notice flicker unless the screen is refreshed at least 50 times per second but LCD monitors have a refresh rate of 60 times per second so are 'flicker free'.
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Frame Rate
The number of frames displayed per second. To see continuous (smooth) motion, the human eye needs a frame rate of at least 25 frames per second.
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Interlaced Encoding
The image for each frame is split into even lines and odd lines. The first half (odd lines) of the image is displayed completely then the second half (even lines). This appears to have a high refresh rate and halves the transmission bandwidth needed.
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Progressive Encoding
The full frame is displayed each time (all lines are drawn in sequence). Motion therefore appears smoother and more realistic.
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Frame Resolution
The number of lines per frame x the number of pixels per line.
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Lossy Compression
An encoding technique that reduces file size by removing data. Once this has occurred, it is impossible to recreate the original file. It is used to compress image and sound files where the human eye/ ear will hardly notice the difference. JPEG file.
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Lossless Compression
An encoding technique that reduces file size without removing data. The compressed file can be decoded to recreate the original file. Used for e.g. text files where we don't want to lose any data. PNG file.
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Huffman Coding
Lossless compression technique. The most often used characters are given shorter character codes (instead of 8 bits). This reduces the number of bits in the compressed file and the Huffman codes can be decoded.
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Run-length Encoding
Lossless compression technique. Often used for compressing bitmap files. It converts sequences of the same bit pattern into a code defining the bit pattern and the number of times it is repeated.
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Spatial Redundancy
Redundancy within a single picture e.g. repeated pixel values in a large area of blue sky. Image file compression (e.g. run-length encoding) relies of spatial redundancy.
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Temporal Redundancy
It exists between successive pictures e.g. the current frame and the subsequent frame in a video file. Where relatively little changed from one frame to the next.
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Interframe compression
Used for compressing video files. It relies on temporal redundancy. The first frame is sent and encoded and for the next frame, only the changes between this and the previous one are sent. The decoded adds the differences to the current frame.
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Multimedia Container Format
A file format containing both audio and video data in a standard container thereby allowing simultaneous (synchronised) playback. It is simply used to identify and interleave the different data types inside it.
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Stand-alone Computer
Any computer not connected to another.
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A set of connected computers and other devices used to share resources including software, hardware and data. Computers can be connected with wires or without wires.
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A Local Area Network is located at one location/site e.g. a building or campus. The cabling and hardware is usually owned by the organisation e.g. the school.
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A Metropolitan Area Network covers a wide but defined area such as a city.
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A Wide Area Network covers a wide geographical area e.g a company may have several offices that they want to connect. This often involves connecting several LANs that are usually connected with infrastructure owned by telecoms companies.
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Copper Cable - UTP
Unshielded Twisted Pair is a pair of copper cables twisted together. It is designed to cancel out electromagnetic interference. They are thin, easy to install and are often used in LANs. They are used to connect phone handsets to the telephone line.
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Copper Cable - Coaxial
A central single strand wire insulated from the outer metallic shield. It is bulky and unsuitable for large installations. The metal shield protects signals from outside interference.
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Fibre Optic Cable
It is up to 24 glass strands in a single cable. Signals are sent using light which can travel long distances and the signals lose less strength than those in metal cables. They are more expensive and carry a greater bandwidth than metal cables.
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The Internet
It is a network of networks that are joined through interconnected gateways/routers using the TCP/IP protocol. Data is sent in packets with a source address and destination address. There are many paths the packet can take.
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The World Wide Web
It is a set of web pages that are 'hosted' on the internet.
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Public Switch Telephone Network is infrastructure originally designed to provide the public telephone network. It is able to carry analogue signals and is now part of the internet's infrastructure. Use of the PSTN requires a modem.
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A modulator/demodulator is used to send signals over the intenet via the phone network. The phone's digital signal must be converted to an analogue signal. Modems convert between the two. E.g. the PSTN uses analogue signals but phones use digital.
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An Internet Service Provider is a company (e.g. BT, Virgin etc.) that provides the user with access to the internet. They usually charge a monthly fee for the service and they provide broadband network connections and Wi-Fi hotspot technologies.
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Dedicated or Leased Line
A communication link between two points that is available for use 24 hours a day by a designated user. Many companies use this as opposed to the PSTN which is a shared infrastructure. They are fast and reliable but expensive.
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Cell phone Networks
Geographical areas are divided into hexagonal cells, each of which is served by at least one transmitter and uses a different frequency to its neighbouring cells. It is most commonly used for communication from phone to base station using radio wave.
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They allow us to connect network components that are great distances apart. Communication can be affected by transmission delays.
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GEO Satellites
Global Earth Orbit satellites are at high altitude and provide long distance telephone and computer network communication.
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MEO Satellites
Medium Earth Orbit Satellites provide GPS (Global Positioning System) services.
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LEO Satellites
Low Earth Orbit Satellites support the phone networks.
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A Network Interface Card is electronic circuitry that enables a computer to connect to the network by preparing the signal for the network.
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Signals can lose strength (attenuation) or may become corrupted along a medium (a wire). Repeaters strengthen or improve the signal and send it on to the next part of the network.
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They are similar to repeaters but have more than one output port. It is a device that allows us to connect many devices in one segment of the network to the rest of the network.
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It connects different networks of a similar type. it sends data from one segment of the network to another.
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It is a high speed multi-port (many connections) bridge.
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It connects networks that have different underlying technologies (protocols). A network gateway can be software, hardware or a combination of the two. Because they are on the 'edge' of the network, they sometimes include a firewall.
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It allows us to connect multiple networks (both internal and external) so that we can send data packets between them. The router gives each packet of data a destination address.
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A computer on a network that provides services and runs specialist software.
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File Server
It stores network users' data files.
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Print Server
It manages the printers that are connected to the network.
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Communications/ Web Server
It handles many common communications functions for the network such as e-mail, remote access, firewalls or internet services.
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Application Server
It shares network-enabled versions of common application software.
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Database Server
It manages common databases for the network.
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It sits between the user's computer or network and another network such as the internet. They are used to improve performance (by using a feature known as Cache) and they improve security.
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Client-Server Architechture
The servers run specialist software that is available to non-specialist computers (clients). Clients send requests across the network to the appropriate server. The server sends the response back to the client device.
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Real-Time Bit Streaming
This allows a user to watch 'live' events that are usually used on mobile and other devices over a wireless connection.
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On Demand Bit Streaming
It allows the user to 'catch-up' on broadcast that they may have missed. The bit stream is saved to the device's secondary storage (hard drive) and can then be watched by the user when convenient.
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The rules that control communication between devices. They need to be able to identify themselves and others and start, manages and end exchange of data.
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File Transfer Protocol sets the rules for copying files from one computer to another.
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Hypertext Transfer Protocol sets the rules for distributing web pages.
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Transmission Control Protocol/Internet Protocol sets the rules that allow devices to send data over the internet.
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IP Address
Every device connected to the internet is given a unique address known as the Internet Protocol Address so that they can send and receive data. It is a 32-bit number so can have around 4 billion combinations. A home computer is given one by the ISP.
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IPv4 Address
A 32-bit hierarchical address of a device on the internet. It is version 4 of the IP addressing system.
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All 4 billion IPv4 addresses had been exhausted in 2011 so IPv6 is a 128-bit addressing scheme that can support a much greater number of devices.
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Addressing Scheme
The method used to identify a device on a network. It determines how many bits in the IP address are used to identify the network and how many bits are used to determine the host.
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Classless Inter-domain Routing is an addressing scheme that allows a more flexible allocation of IP addresses than the original system of IP address classes. It allows the split between the netID and the hostID to be varied to suit individual needs.
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Network Address Translation is a mechanism for translating between private IP addresses and public internet IP addresses.
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They are private networks that large organisations are able to have. They are based upon internet technology (TCP/IP).
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It is a programming language that can be used to add interactivity to web pages. It is used when the programmer when the programmer wants the client computer to do some processing which is known as client-side processing.
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It is a programming language that is used for server-side processing i.e any processing that the server needs to do to support the application.
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Input Device
Input devices allow us to enter data into a computer.
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Optical Character Recognition software is able to recognise text within a scanned document (image) and convert this into a text file format that can be edited.
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Pointing Devices
They are used to select or 'click' on an icon, menu item etc. It can connect to a computer using a USB cable or using a wireless connection.
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Primary Memory
It is the computer memory that the processor accesses first/directly allowing the processor to access running applications and services that are temporarily stored in a specific memory location. It is made up of RAM and ROM.
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Secondary Storage
It is computer memory that is non-volatile and is not directly accessed by the processor. The primary/main memory accesses the secondary memory so this is slower than primary memory. It consists of hard disk drives and solid state drives.
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Auxiliary/ Off-line Storage
It is also known as external memory. It is not accessible by the CPU. It has slower access rates but a big storage capacity and is non-volatile. It stores inactive programs. It is e.g. DVD/CD, USB/Flash memory sticks or a removable hard drive.
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A storage location that exists on the processor itself so has an even faster access time than Cache memory.
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Cache Memory
A type of RAM that is faster to access the main memory RAM.
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Volatile memory that can be read from or written to any number of times. It is used to store data and programs that the computer is currently using.
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Each DRAM chip contains millions of tiny capacitors and transistors. The capacitor holds the bits of information but the electrical charge leaks away over time so DRAM needs to be refreshed otherwise the charge will be left as 0.
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It uses 'flip flops' (a special electronic circuit) which hold each bit so it doesn't need to be constantly refreshed like DRAM. SRAM is much faster so is often used for cache memory.
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Non-volatile memory that cannot be written to but can be read from any number of times. ROM stores the start-up instructions for when the computer is first turned on and other programs that will not be changed. It is programmed during manufacture.
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Hard Disk Drives (HDD)
The most common method for storing data on a computer. it has a magnetic surface onto which digital information is stored. The magnetisation of the surface can be interpreted as 1s and 0s. Data is stored in sectors and tracks.
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The time taken for a specific block of data on a track to rotate around to the read-write head.
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Solid State Drives (SSD)
It has no moving parts. The data is stored as 1s and 0s in millions of tiny transistors on NAND type memory chips which is also known as Flash memory and is a non-volatile re-writable memory.
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USB/Flash Memory Sticks
Solid state technology with no moving parts made up of NAND chips. They are small and lightweight. It is used to transfer files between devices and used for backups.
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Removable Hard Disk Drives
They are hard disk drives that connect to the computer via a USB connection and are used as a backup or to transfer files between devices.
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CDs and DVDs
They are optical storage devices. Laser light is used to read from/write data int the surface. It uses a single, spiral track and the data is stored in 'pits' and 'lands'. Data is burned onto the metal surface which is melted.
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It is an optical storage media where the data is stored in concentric tracks allowing for simultaneous read and write operations to take place.
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Blu-ray Disks
It is an optical storage media. A blue laser is used to carry out read/write operations. DVDs and CDs use a red laser which has a larger wavelength than the blue laser so the bumps in blu-ray are smaller. Blu-ray can store 5x as much data as a DVD.
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Output Device
Data is sent from a computer to output devices.
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Liquid Crystal Display is a screen back-lit by light emitting diodes and with liquid crystal cells between polarisers.
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Light Emitting Diodes that emit very bright white light.
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Organic Light Emitting Diodes use organic materials such as carbon compounds. They can be used to both emit light and control the colour.
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Logic Proposition
A statement that is either TRUE or FALSE e.g. London is further south than Manchester.
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Problem Statement
An outcome that is dependent upon one logic proposition or a combination of two or more logic proposition. E.g. you should take an umbrella if a) it is raining or if b) the weather forecast is for rain later.
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Boolean Operators
They are used to help us express problem statements more formally i.e. help us write logic expressions.
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Logic Expression
They are logic propositions combined with boolean operators which may be written with a defined outcome.
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Logic Gates
They are a type of electronic circuit that controls the flow of electricity. The basic operation of the circuit is that it is either ON (1) or OFF (0). The physical circuits are comprised of transistors.
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Logic Circuits
Logic gates that are combined to carry out a particular function.
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Stored Program Computer/ Von Neumann Architecture
The idea that there is a processor which has access to memory/storage. The memory contains a 'stored program' (instructions) and data which move between the memory and the processor (executes the instructions sequentially).
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Computer Memory (Memory Unit)
A device for storing computer program instructions and data which are loaded into memory and held at specific memory locations which have addresses. Computer memory is made up of partitions consisting of an address and its contents.
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The central processing unit is responsible for executing or processing the instructions in a computer program.
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The Arithmetic Logic Unit is responsible for the arithmetic and logic processing needed by a program.
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Control Unit
It controls the flow of data through the CPU and the whole computer system and ensures that the program instructions are handled correctly.
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They are high speed temporary storage locations on the processor. They help the processor do its job by storing the data the processor needs to process each instruction. Data is constantly moving in and out of the registers.
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It stores a value before and after the execution of an instruction by the ALU. It contains the value to be used by the ALU for the execution of an instruction and can store a value after the execution of an instruction.
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PC (Program Counter)
A register that stores the memory address of the next instruction to be executed.
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CIR (Current Instruction Register)
A register that stores the instruction currently being executed.
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MAR (Memory Address Register)
A register that stores the memory address from which we want to read data or write data to.
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MDR (Memory Data Register)
A register that stores the data we've read from memory or we are going to write to memory.
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IX (Index Register)
It stores a value but is only used for indexed addressing.
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SR (Status Register)
It is used when an instruction requires arithmetic or logic processing and contains individual bits that are either set or cleared. The bits can be set to 1 if a condition is detected e.g. an arithmetic calculation requires an overflow carry.
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They are connections (like wires) that link the various parts of the computer together.
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Bus Width
The number of separate wires in the bus. The number of wires defines the number of bits of data that can travel along the bus at any one time.
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Data Bus
It carries data between the processor, memory and input/output devices. The data bus is bi-directional. The data could be an instruction, a value or and address of an input/output device.
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Address Bus
It carries an address to the memory controller to identify a location in memory to be read from or written to. It carries address information between the processor, memory and input/output devices. It is unidirectional (away from the processor).
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Control Bus
It carries control signals between the processor, memory and input/output devices telling them what to do. It carries timing signals dictated by the clock cycle. It is both unidirectional and bi-directional due to the connections inside the computer.
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System Bus
It is a collective term for and is comprised of the address, data and control bus.
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The Universal Serial Bus has become the standard for transmitting data between a computer and devices. The 4 wires in a USB cable are for Power, Earth and 2 are for data transmission.
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Machine Code
The only language that the CPU recognises is machine code i.e. binary codes.
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Machine Code Instruction
A binary code that can be recognised and executed by the CPU. They have a defined number of bits.
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Instruction Set
The complete set of machine code instructions that can be recognised and executed by the CPU. Different processors have different instruction sets. Even if 2 processors have the same instruction, usually, the machine code is different for each.
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A sequence of instructions that is often used as a repeatable block of code. It can be called from within the code and the macro name is replaced with the code resulting in an increase in program size.
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A sequence of instructions that is often used as a repeatable block of code.
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Instructions to the assembler. It is the software that translates the assembly code into machine code. It instructs the assembler how to construct the final executable machine code.
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System Calls
They allow the code to use operating system commands e.g. for reading a file.
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Operating System
A software platform that provides facilities for programs to be run which are of benefit to a user. It is an example of system software.
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User System Interface
The interface through which the user interacts with the computer.
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Command Line Interface
The user types commands into the computer to perform actions. The user needs to know what commands are available and what to do so some expertise is required. Thus this is not user friendly.
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Graphical User Interface (GUI)
The user selects icons and menu items to perform actions. Pointing devices are used to move a cursor around a screen. More than one window can be used and this is relatively user friendly.
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Programmer-Hardware Interface
Programmers write software applications. The OS ensures the hardware does what the programmed software wants it to do. The OS provides the mechanism for the execution of the developed application.
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Resource Management
Each process (a program that has begun execution of which there may be many) needs to access the resources provided by the computer system. The OS aims to achieve optimum efficiency in the system by scheduling the processes and resolving conflicts.
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Memory Protection
It ensures that one program does not try to use the same memory location as another program.
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Memory Usage Optimisation
It involves deciding which processes should be in main memory at any one time and where they should be stored.
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The Memory Organisation Scheme
It is chosen to achieve optimum usage of a limited memory size e.g. virtual memory using paging or segmentation.
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Virtual Memory
Memory that appears to exist as main storage although most of it is supported by data held in secondary storage with the transfer between the two being made automatically as required.
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Device Managment
It is where the usage of the device is controlled by the OS following installation of device driver software.
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File Management
The OS provides file naming conventions, directory/folder structures and access control mechanisms.
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Security Management
The OS provides provision for recovery when data is lost, prevention of intrusion (a firewall) and ensuring data privacy.
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Hard Disk Formatter Utility
It is a software utility that removes data from the disk, sets up a file system on the disk and partitions the disk into logical drives.
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Hard Disk Contents Analysis Utility
It is a software utility that checks for errors on the disk.
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Disk Repair Utility
A software utility that can mark bad sectors so the system doesn't try to use them and it may be able to recover some damaged data, otherwise it deletes it from the file system.
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Hard Disk Defragmenter utility
A software utility that reorganises the file storage so that all files are stored in 'contiguous' sectors.
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Backup Software Utility
A software utility that is able to create backup files, establish a schedule for backups and will only create a new backup file when there has been a change.
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File Compression Utility
A software utility that can be used to compress files to minimise hard disk storage.
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Virus Checker
A software utility that scans a computer for viruses and other malware. It reports and 'quarantines' any viruses found and/or deletes them.
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Program Library
It is a file that contains code/routines that can be used by other programs. Programmers have access to these and can incorporate the library routines in their code. It saves time as the programmer can use the code that has already been written.
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A Dynamic Link Library is a file containing a library of routines that can be accessed by another program. For static links, the .dll files will be in use as long as the program is active but for dynamic links, the files are only in use when needed.
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Programmes are written in high-level language that humans can understand. A Translator is a software program that translates the program into binary that the computer can understand.
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A computer program that translates assembly language programs into machine code (binary code). It creates an object file (contains machine code but is not executable).
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Software that is used to combine one or more object files into an executable.
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OS software that is used to bring the executable program into memory and starts execution.
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A computer program that reads our high-level language programs (e.g. Python) line by line and performs the required actions. Interpreted programs cannot be used without an interpreter as an executable file of machine code is not produced.
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Software that translates a program written in a high-level language into a machine code version of the program. This executable file can then be used again and again without recompilation so they can be distributed for use without the source code.
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JVM (Java Virtual Machine)
Software that can be installed on any computer with any processor type. Programmes written in Java are compiled to produce Java Bytecode that can be interpreted by any JVM regardless of the computer's processor.
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Data Integrity
A requirement for data to be accurate and up to date.
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Data Security
A requirement for data to be recoverable if it is lost or corrupted.
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Data Privacy
A requirement for data to only be available to authorised users.
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Data Protection Legislation
Laws designed to protect how personal/private data can be processed e.g. the organisation can only use the data collected for purposes understood and agreed by the individual.
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Business Continuity Plan
A plan that organisations typically have to outline the actions it will take after a disruptive incident.
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Disaster Recovery Plan
A part of the business continuity plan that outlines the process and procedures to recover and protect IT services in the event of a disaster.
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User Account
A user account is a location on the network server used to store a computer username and password.
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The verification of a user's identity. It is the main feature of a user account including methods such as a password and biometrics e.g. fingerprint or retina scans.
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Anti-Virus Software
It scans the system for viruses and other malware and removes or deactivates them.
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Intrusion Detection Software
It reviews the system usage data and looks for potential issues.
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This can be software or hardware. It sits between the user's computer and external network (internet) checking information coming from the external network and either blocks it or allows it to pass.
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Digital Certificates
These are issued by Certification Authorities containing the owner name, a serial number, valid from and to dates and a public encryption key and they are used to authenticate the sender of emails. This is sent with the email.
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Digital Signatures
A digital code that is attached to a document to verify its sender and contents.
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Disk Mirroring
During the normal operation of the system, data is stored on two disk systems which might be at different remote locations. In the event of loss of data on one system, the business can switch to the second 'mirror' disk and continue work as normal.
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The definition of a user's access rights to the system components which are set by the system administrator.
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The process of 'scrambling' data is such a way that only someone with the secret code or key can read it.
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Plain Text
The normal representation of the text or data before the data gets encrypted.
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Cipher text
The encrypted version of the plain text.
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The process of taking cipher text and converting it back into plain text.
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Encryption key
A random string of bits created for encrypting and decrypting data. It is usually a series of 0s and 1s. It is designed with an algorithm to ensure every key is unpredictable and unique.
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Encryption Algorithm
The process that uses the key to encrypt the data. It uses maths and logic to 'mix' the key with the data so that the data becomes unreadable. Different keys can be used with the same algorithm to produce different results.
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Data Validation
A check that the data entered is the correct type and format. It does not guarantee that the data is accurate.
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Presence Check
Ensures that the field is not left blank.
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Format Check
Ensures that data is in the correct format e.g. a date must be DD/MM/YY
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Length Check
Ensures that the length of the data is not too long or too short e.g. a password should be more than 8 characters but a surname should be fewer than 20 characters.
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Range Check
Ensures that the data is within certain limits e.g. age is > 18.
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Type Check
Ensures that the correct data type is entered e.g. a certain field should only contain integers.
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Data Verification
Confirmation of the data received by a system e.g. when you change a password, you are asked to enter it twice so that it can be verified.
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This is the result of a calculation made using data before it is transmitted.
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Parity Checking
A process by which the number of '1' bits is counted and this must be the same in the delivered file as it was in the sent file. Even or odd parity checking can be used.
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Parity Blocks
Similar to parity checking but the number of '1' bits in each row and column of a block of data is counted. A parity bit and the most significant bit of each byte is used to confirm whether the number of '1' bits in that row/column is even or odd.
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Computer Ethics
The moral principles governing the design, building, implementation and use of computer systems.
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Code of Conduct
A set of rules or practices defining how a group or organisation should behave. They protect both the organisation and the individuals. They are also applied to ensure computers are used safely and lawfully.
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ACM/IEEE Software Code of Ethics
The Association for Computer Machinery/ The Institute of Electrical and Electronic Engineers presents a set of 8 fundamental principles. The code provides a framework for ethical judgement.
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The formal recognition of ownership of a created or published work.
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Copyright Legislation
It is in place to protect the author of the original works. It includes a requirement for registration e.g. date of creation, a period when copyright applies and a policy for when the copyright holder dies.
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Internet Piracy
The illegal copying of a product e.g. a movie could be 'ripped' from a disk to be streamed over the internet.
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Digital Rights Management is used to prevent 'ripping'. It restricts the way in which content can be copied e.g. using encryption, embedded code to prevent copying or only allowing playback with a disk present. These do not all prevent piracy.
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Commercial Software
Copyrighted software that almost always has to be paid for e.g. Microsoft Office.
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Open Source Software
Software that is distributed for free with unlimited uses allowed and access to the source code is provided.
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Open Source Intitiative
This makes open source software, including the source code, available for free. It encourages collaborative development. The user of the software is free to use, modify, copy and distribute the software.
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Copyrighted Software that is distributed for free with unlimited use allowed but no source code is provided so the software cannot be modified.
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Copyrighted software that is distributed for free for a limited period with no source code provided. It often contains a limited version of the software and allows users to try before they buy.
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The Free Software Foundation
This has similar objectives to the Open Source Initiative but any software modified by any user must be made available under the same conditions of usage, known as 'copyleft'.
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A database is a persistent, organised store of related data.
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Flat File Database
A database holding data in a single file/table.
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Data Redundancy
The same data is being stored more than once (duplicates).
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Relational Database
A model in which data is stored in a collection of relational tables each known as a 'relation'.
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Something in real life about which we record data or information.
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The implementation of an entity in a relational database.The tables are given names that reflect the data to be held within them.
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One of the data items for an entity; a column (field) in a relation that contains values.
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The data for one row in a table.
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Primary Key
A field that is used to uniquely identify each record in the table. An attribute/combination of attributes for which there is a value in each record/tuple and that value is unique. Every record/value in a table must have a value for the primary key.
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Candidate Key
There could be more than one attribute that would act as the primary key. If so, each attribute is said to be a candidate key (each is a contender for the primary key).
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Composite Key
A primary key comprised of more than one field.
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Referential Integrity
Data stored in tables must obey the relationships that exist e.g. it should not be possible for a product name in an order to exist on the order table if the product does not exist on the product table.
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Foreign Key
An attribute in one table that refers to the primary key in another table. They allow one table to be related to another.
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A technique for constructing a set of table designs from a list of data items ensuring that the tables will contain no redundant data.
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First Normal Form (1NF)
This states that there should be no repeated groups of attributes.
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Second Normal Form (2NF)
This applies to tables where there is a composite key. It states that the non-key attributes in the table must be dependent on knowing all of the primary key. If any non-key attribute can be determined from just one part of the key, it isn't in 2NF.
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Third Normal Form (3NF)
This states that there must not be any dependency between non-key attributes. If any non-key attribute can be determined from another non-key attribute, the table is not in 3NF.
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Structured Query Language is a programming language provided by the Database Management Software (DBMS) to support the creation and maintenance of a relational database.
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Data Definition Language is the part of SQL that is provided for creating or altering the table.
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Data Manipulation Language is the part of SQL used for adding, updating or deleting data and running queries.
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Database Management Software is used to define, create and query a large collection of data. It controls access to data in a database.
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Data Dictionary
A part of the database that contains definitions of the tables, attributes, queries etc. and how the physical storage is organised. It contains metadata about the data.
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Base 16 numbering system with digits 0-F.


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Card 4


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Card 5


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