Computer Systems Data Representation - Key word definitions

Transcription

1 Computer Systems Data Representation - Key word definitions Why do computers use Binary to Simplicity of Electrical two-state (on =1, off = 0) represent everything? Slight fluctuations in voltage have little effect on binary values Fewer and simpler rules for arithmetic in binary. Floating point numbers for number with fractions mantissa & exponent 5.6 x 10 8 ASCII 8-bit code for representing text Character set All the letters, numbers and symbols possible on a system Control characters Non-printable ASCII codes that carry out control functions Byte 8 bits Kilobyte 1024 bytes Megabyte 1024 x 1024 bytes (approximately 1 million bytes) Gigabyte 1024 x 1024 x 1024 bytes (approximately 1000 million bytes) Bitmap (for graphics) each pixel is mapped to (represented by) bits. Pixels The little dots that form images on a computer screen or on printouts Resolution A measure of how many pixels there are in an image dpi (dots per inch)

2 Computer Systems Computer Structure - Key word definitions CPU Arithmetic and Logic Unit (ALU) Registers Control Unit Main memory Backing storage Unique Address RAM ROM Clock Speed Embedded System Brain of computer consists of processor and main memory The component of the processor which performs arithmetic calculations and processes logical conditions (AND, OR). Fast access temporary storage locations inside the processor that are used to handle the data currently being processed. The component of the processor which controls the flow of data and instructions in and out of the processor. Where the programs and data currently being used are stored Permanent storage for programs and files outwith the CPU itself until we are ready to use them. DON T confuse with memory!! Required by every memory location so that the processor knows where to store and retrieve data Type of memory which can be loaded into but its contents are lost when the computer is switched off Type of memory which the computer system uses but we cannot change. Retains its contents when the power is switched off. Number of ticks per second. A simple indicator of processor speed. A system, appliance or device with an integrated processor dedicated to one task.

3 Computer Systems Peripherals - Key word definitions Peripheral Interface CCD Charge Coupled Device OCR Optical Character Recognition TFT - Thin Film Transistor Printers Flash (Pen) Drive Hard disk Magnetic Tape Cartridge CD-R/RW DVD R/RW Any device connected to (or on the edge of) the CPU Circuitry which allows devices to connect with and communicate with the CPU Functions of an interface data conversion & data storage Chip in digital camera which captures the photo. Made up of a grid of millions of light sensors. Each sensor records a pixel value. Software which enables scanners to convert text on paper documents into editable text. The most common type of flat panel LCD monitor Laser & Inkjet speed (ppm), resolution (dpi), initial costs v running costs The most convenient and portable backing storage medium in use today. Plugs into USB slots. High capacity, random access, fast access backing storage, GB Cheap, for backup, sequential access A type of optical storage medium capacity 700 MB A type of optical storage medium capacity 4.7 GB

4 Computer Systems Networking - Key word definitions LAN Local Area Network Limited range within 1 mile Dedicated cabling (or wireless) High bandwidth and more reliable WAN Wide area network Extensive range spans towns & countries Uses existing telecommunications technologies phone, cable, satellite Lower bandwidth and less reliable Bandwidth Amount of data that can be transferred across a network per second Client - server Client a workstation on the network Server system that provides resources to the other networked machines Network resources (or functions) Network Benefits Internet WWW World Wide Web HTML Hypertext Markup Language Web Browser Creating web pages Search Engine Address Book Mailing list folders Data Protection Act Computer Misuse Act File server, server, Printer Server, Internet server Communication sending s & sharing files, Sharing hardware share printers and Internet connection, Security only valid users can gain access to network (on client server), Centralised storage can access files on server from any machine The physical worldwide network infrastructure made up of computer systems and networking hardware all interconnected with telecommunications technology. Mainly a software entity - millions of interconnected web page documents stored on servers on the Internet. The universal language used to describe to web browsers how web pages should be displayed. Software for viewing and navigating around web pages. Address bar, hyperlink, back/forward, bookmarks (favourites), history. Using a text editor to enter and edit HTML code or a web authoring package. A large database on an Internet server containing a list of all known websites and their content. Users can do keyword searches e.g. Google. Send and receive textual messages and attachments via the Internet. Keeps an index of contacts and their addresses. A group of addresses organised under a one heading for multiple mailings. A way of grouping together received s. Filtering rules can be applied. Protects data subjects (people) from misuse of data stored about them by data controllers. Make hacking illegal (unauthorised access to computer systems and data on them)

5 Computer Systems Software - Key word definitions Operating System Software which controls the operation of the computer e.g. Windows XP, Vista Application Software Software designed to allow users to carry out specific tasks e.g. word processing, databases, graphics, , games. Objects (associated with applications) The data objects that can be manipulated and edited in a package e.g. text, table in word processing and row, column, cell in spreadsheets etc. Operation (associated with The feature or function that is performed on (or applied to) a particular data object applications) e.g. copy, paste, insert, delete, change font, size, move, scale graphic. Standard File Format Allows documents created with one package to be opened by other packages portability. e.g..txt, RTF, JPEG Virus Program written to make a computer system behave abnormally or become corrupt. Must be executed or opened to cause any harm, replicates. Virus Symptoms System runs slow, freezes, odd messages and sounds, lots of junk suddenly, web browser redirects itself to dodgy web sites. Causes of Infection Removable media infected disks, pen drives, CD s. attachments Downloads infected software from dis-reputable sites. Anti Virus Software Helps prevent virus infection. Can detect and remove existing viruses. Disadvantage is that it often slows computer down especially at startup.