Computer Science Exam Revision and Answer provided

Cambridge IGCSE Computer Science HTTP - hypertext transfer protocol - ANS-a set of rules which must be followed when transferring files across the internet URL - uniform resource locator - ANS-used to find/identify a webpage on the internet 1. webserver name 2. file name 3. protocol web browser - ANS-software that allows a user to display a webpage on their screen - they interpret html code and show the result actuator - ANS-used in many control operations involving sensors and ADC/DACs. Electromagnetic device eg. motor that outputs result of sensor operation loudspeaker - ANS-output device that produces sound using voltages at different levels which vibrate a cone in speaker housing LED - ANS-Used for backlighting a monitor/tv - they are thin, produce a white light, and do not require much power CCFL - ANS-Old technology used for backlighting - took time to warm up, and produced yellow-ish lighting + required a lot of power volatile - ANS-memory that loses its contents when the power is off eg. main memory non-volatile - ANS-memory that doesn't lose its contents when the power is off e.g. hard disk off-line storage - ANS-storage that can be physically moved away from a device and stored somewhere else e.g. CD, USB stick, DVD SRAM - ANS-type of RAM that has 'flip flops' to hold each bit of memory. Does not need constant refreshing. magnetic media - ANS-secondary storage with mechanical parts which move over the surface to read and write data magnetically e.g. a hard disk, tape or floppy disk program - ANS-our way of telling a computer what to do, how to do it, and when to do it assembly language - ANS-code that is specific to a particular hardware, but needs to be translated into machine code before it can run machine code - ANS-the binary code that is specific to a machine and does not need translating in order to run translator - ANS-program that changes higher level language into machine code compiler - ANS-this translates HLL into machine code. Once it has done this, the program can be used multiple times without translating it again UPS - ANS-uninterruptable power supply cracking - ANS-editing source code with malicious intent firewall - ANS-this examines traffic between a user's computer and the internet by checking what is/isn't allowed and blocking traffic that does not meet certain criteria proxy server - ANS-this filters web traffic, keeps the IP address secret, and, using a cache, speeds up access to websites that have been visited before TLS - Transport Layer Security - ANS-this is a form of secure data transmission made up of 2 layers: the record protocol, and the handshaking protocol. It is very secure and fairly new, and can make use of session caching, which improves performance. It involves many complicated encryption algorithms. prevents third party hacking into communication between web server and the user's computer. session caching - ANS-this is used in TLS to avoid using too much computer time; TLS is able to attempt to resume an existing session, which increases speed. Denial of Service (DoS) attack - ANS-attempting to prevent a user from accessing part of a network (usually the server); this is usually temporary, but may be very damaging, or a big security breach. overloads web traffic by sending thousands of requests. free software - ANS-software that is free to run, copy, change or adapt, and share with friends, family or colleagues. CSS - ANS-Cascading Style Sheet. Controls presentation of page. Enable multiple pages or elements on a page to be changed in one go. Gigabyte (GB) - ANS-1024 megabytes. 2 to the power of 30 bytes. HTML - ANS-HyperText Mark-up Language. Used to write and develop webpages to present text. Uses tags. Terabyte (TB) - ANS-1024 gigabytes. 2 to the power of 40 bytes. Lossless image compression - ANS-Find groups of repeating data. Records the data once and the number of times it was repeated. Lossless text compression - ANS-Finds patterns in original text. Encodes each pattern in a dictionary PNG - ANS-Lossless picture file format that uses alpha channel to keep transparent backgrounds. MIDI - ANS-A set of instructions for digital instruments to play synthesised sounds. Musical Instrument Digital Interface. .WAV - ANS-uncompressed music files .FLAC - ANS-lossless compressed music files Parity bit - ANS-Set to 1 or 0. Sent with a byte of data to make the total number of 1s odd or even for each byte. 1KB (kilobyte) - ANS-1,024 bytes (2¹⁰ bits) 1MB (megabyte) - ANS-(2²⁰ bits) 1GB (gigabyte) - ANS-(2³⁰ bits) 1TB (terabyte) - ANS-(2⁴⁰ bits) 1PB (petabyte) - ANS-(2⁵⁰ bits) A - ANS-10 B - ANS-11 C - ANS-12 D - ANS-13 E - ANS-14 F - ANS-15 Simplex - ANS-Data sent in 1 direction only Asynchronous - ANS-Agreed bit pattern with control bits Parity Check - ANS-Uses parity bits. Odd Parity / Even Parity agreed between sender and receiver. If it is not the agreed number, an error has occurred. ARQ (Automatic Repeat Request) - ANS-Uses acknowledgement and timeout. If acknowledgement isn't sent back to sender before the timeout occurs, message automatically resent. Checksum - ANS-Additional value sent at the end of a data block. When block is about to be transmitted, additional value calculated and then transmitted. Value recalculated at the end to make sure they match. If they don't match, an error has occurred. Echo Check - ANS-Data sent to and from another device twice. Sender compares 2 sets of data, if the sets of data are different, an error has occurred. Wardriving - ANS-Using wireless internet connections illegally through a portable device Secure Sockets Layer (SSL) - ANS-When a user logs onto a website, it encrypts the data. Only the user's computer + web server can make sense of what's being said. A green padlock in the status bar. Record Protocol - ANS-Can be used with or without encryption Handshake Protocol - ANS-Permits the website and user to authenticate and make use of encryption algorithms which only the user and website know. Encryption - ANS-Makes data meaningless unless recipient has the decryption key Asymmetric Encryption - ANS-Private and public key are both needed. Encryption keys generated using a hashing algorithm. Authentication - ANS-Used to verify data is coming from a trusted source. MAC address - ANS-a number that uniquely identifies a device on the Internet. Often refers to network card. Rarely changed. ISP (internet service provider) - ANS-company charging monthly fee that provides internet access IP (internet protocol) address - ANS-assigned by ISP, unique to each internet session MAC address - ANS-number which uniquely identifies a device - 1st half = manufacturer, 2nd = device itself - made up of 6 groups of hex digits HTML Presentation - ANS-how the document looks/sounds HTTPS - ANS-a SECURE set of rules which must be followed when transferring files across the interne