Gcse Ocr Computer Science

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Input Device

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Device used to enter data into a device for processing.

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Output Device

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Device used to present information.

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Storage Device

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Device used to store data or processing later on.

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SSD

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A storage device with no moving parts. Not sensitive to movement. Useful for transporting data. Relatively expensive.

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Magnetic Storage Device

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A HDD. Has a high capacity of storage available. Sensitive to movement due to moving parts. Used as main storage for computers.

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Optical Storage Device

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A storage device read by a laser.

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Binary

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Can be a 0 or 1 used so that computers can be based on electronic logic circuits.

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CPU

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Performs processing on a computer. Fetches instructions from memory. Decodes instructions. Executes instructions.

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Clock Speed

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The higher the clock speed the faster the CPU will run. Represents the number of instructions the CPU can process in a given time.

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RAM

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Stores OS programs and data that are currently in uses. Volatile = all the contents are lost when the PC is turned off. More memory means programs will run faster due to less use of virtual memory.

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ROM

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Loads the start-up program used to boot up the computer when it is switched on. Loads the OS.

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Virtual Memory

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A section of the hard disk is used to act as RAM. Allows more programs to be loaded.

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Anti-Virus

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Regularly checks computer for programs designed to harm the system. Disables and deletes these programs.

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Disk Defragment

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Reorganizes files so that they are stored in blocks next to each other. Free's space.

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Disk Cleanup

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Searches for and deletes files which are no longer needed. Free's up space which can be used for other programs.

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System Cleanup

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Searches the computer for files/programs which are no longer needed.

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System Update

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Search on the internet for updated versions of the software on the computer and downloads/installs the updates.

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Bespoke/Custom Software

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Software created especially for a user. Useful if appropriate software may not exist.

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Open Source Software

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License-free source code is available for others to use. Large community of open source developers can see and comment on the code. Free. Can be modified.

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Off the Shelf Software

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Available to buy straight away. Less likely to contain bugs. Costs less. More support. May contain features which aren't needed. May not contain features required. Developer not available to make any adjustments if needed.

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ASCII

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Each character on a keyboard is given a numeric code. Code is then stored in binary. Each character takes 1 byte.

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Bitmap Image

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Picture split into pixels. Each pixel given a binary code.

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Image Resolution

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The concentration of pixels in an image.The higher the res the more pixels are needed.

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DBMS

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Database management system. Software used to manage the database. Allows database to be searched. Provides facilities for creating tables and inserting data.

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Database Form

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An input screen allowing chosen data items to be displayed and edited.

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Database Report

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An output of the data in a database.

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Entity

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A real world object which data is stored in a database.

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Attribute

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A field in a database. An attributes of an entity.

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Primary Key

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Unique identifier within a table that identifies a record.

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Foreign Key

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A primary key in one table that exists within another table.

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Validation

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Ensures data falls within predetermined rules/boundaries.

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Verification

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Ensuring data is entered correctly.

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LAN

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Local Area Network. A network which covers a small area like a house. Can share files and resources. Computers can be managed centrally. Users can communicate with each other. Security and access to data can be managed.

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WAN

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Wide Area Network. Covers wide geographical area. Spans across countries.

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Peer - to - Peer

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All computers have equal status/ no server controlling. To share data between each other. Manageable for networks with a small number of PC's attached. Cheaper to install

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IP Address

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Internet Protocol address. Unique address that is assigned to router attached to network.

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MAC Address

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Media Access Control address. A unique address fixed into a network interface card. Used to identify a device attached to a network.

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Packet

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Data transmitted across networks is broken up into smaller chunks called packets. Sent individually and reassembled at the receiving end.

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Protocol

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Set of rules that govern communications on a network.

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Password

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A string that allows access to a certain part of a system.

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Encryption

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Method of applying a mathematical algorithm to data in order to make it more secure.

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Acceptable Use Policy

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An agreement by a user on what they can and cannot do when using a computer network.

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Backup

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All data on a network is backed up according to a backup policy that states whose job it is to do the back ups how often they will be made and where it will be stored.

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Archiving

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Taking old backup/network data and storing it offline in a secure place.

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Disaster Recovery

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If a network is damaged or destroyed data can be restored quickly to ensure no down time for a business.

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Modem

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Converts digital signals to analogue signals and back again.

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Router

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Connects a LAN to a WAN (connects a network to the internet)

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Server

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Controls access to the network. Checks password entered on any computer. Allows files/resources to be shared. Controls the access of computers to the internet.

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HTML

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Hyper Text Mark-up Language. Text file containing the text to be displayed on a web page. Uses tags which indicate how to display data.

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Compression

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It reduces the size of the file which needs to be transmitted.

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Lossy Compression

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Data is uncompressed it is not exactly the same as the original but the difference is so small that it cant be noticed. (music files)

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Lossless Compression

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When data is uncompressed it is restored completely to the original status. (compressed text files)

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High Level Code

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Instructions use words eg. writeln. Designed to be read by human programmers. Portable/translated to use on different machines.

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Machine Code

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Instructions are in Binary code to be read/executed by the computer. Specific to a particular machine.

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Translator

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Translates one line of high level code at a time and executes it. Stops when it finds an error. Useful for debugging code.

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Translator/Error Diagnostics

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Tools built within an IDE that allow the programmer to check for errors. Tells you what the error is and where it is by underlining incorrect parts of the code. Allows you to enter the corrected code.

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Selection

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Executes code if the criteria is met. For example if statements and case statements.

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Iteration

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Keeps repeating the code until the criteria is met. For example repeat until loop.

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Variable

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An identifier which refers to a location in memory which stores a value which can be changed as the program is running.

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Integer

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A variable data type which is a whole number.

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String

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A variable data type that can only contain letters and/or numbers.

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Boolean

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A variable data type which can be set to either true or false.

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Array

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A group of variables of the same data type stored under one identifier. Each individual variable is given an index number by which it is referred to within the array.

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Syntax Error

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An error in the rules or a programming language.

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Logic Error

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When code compiles and runs but doesn't perform its intended task.

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Test Data

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Data that it used to test a new system.

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Normal Test Data

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Test data that falls within the bounds of the validation rules.

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Extreme Test Data

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Test data that is at the upper or lower limit of the validation rules.

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Erroneous Test Data

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Test data that will force an error on a validation rule. It is purposely incorrect.