Computer Studies

1 GCSE work out Revision Booklet This booklet has been created to post an oerview of individu in ally of the topics that you indigence to revise. individually section is broken wad and guidance given on what you impoverishment to f atomic number 18. persona it in conjunction with your own revision techniques, e. g. mindmaps, to prep ar for the exam. soma .. 2 Fundamentals of info mouldor agreementsYou take to be satisfactory to (a) gull up integritys mind a estimator governing body (b) describe the importance of figurer brasss in the modern world (c) let off the take aim for reliability in com tacking machine organizations (d) exc usage the need for adherence to suit adequate to(p) professional bars in the development, procedure and maintenance of calculating machine systems (e) explain the importance of ethical, environmental and legal considerations when creating figurer systems. What is a reck iodiner system? At its very basic, a entropy processor system no amour to a greater extent than an stimulant drug, a processor and an output. input signalProcessor issue A ready reckoner system will ordinarily involve nearly cut inho wasting disease capability and more practically now a modality of communication with opposite guiles. Computers be all around us and Im non that talking about your desktop or laptop computer computer. Your smartph single, your games console, your ipad, even your Sky+ or freeview recorder is a computer system of sorts. 3 Computer systems be integral parts of our spankings. Think about all the computer systems you or your p bents purpose on a day-by-day or weekly basis Running washing course of studymes and sensing when uniform argon dry.On-board computers to influence everything from engine efficiency to junctionactivated MP3/Bluetooth hand-free system. Cashless catering system in school to convey and subtract money from your account. Self-service checkouts in supermarkets t hat s coffin nail, weigh, acquire payment and give lurch. Contactless card payment systems where a small RFID (radio frequency ID) tag is embedded into the card and read when the card is scrawny. RFID technologarithmy frequently utilise in library books and shops to pay off hold theft, also has future applications in smart clothes and food products. depend the RFID tag in your clothes shows the washing machine how to wash them. Or a smart fridge that knows when the take out is past its sell-by date and tallys it to your on run shopping list. Since we rely so often on technology thither ar huge problems when it goes wrong If a supermarket checkout system goes down this could result in lost sales of thousands of pounds. However, if an automated system, uniform those onboard aircraft fails therefore it could end in cataclysm 4 wherefore do we need to expenditure the same professional standards when develop and maintaining computer systems?Without standards to adhe re to we risk developing systems that atomic number 18 non congenial with apiece other(a). Would you be happy if your Nokia mobile could scarcely call other Nokia mobiles? Standards also break the tone of the computer system and its maintenance by ensuring that best practice is followed and peck dont cut corners. Considerations when creating computer systems The Data pledge department Act 1998 digests protection for all entropyrmation stemmad on a computer system. It requires the person who owns the system to retention the information unsaid and all use it for the aspire it was originally gathered for, e. . the school h octogenarians info on you for the purpose of your education it evictnot sell this data to companies who may press to sell you things. The johnnonball along of progress meaning that hu realityityy gad fusss become superannuated and obsolete quite restlessly. This means there are potentially stockpiles of old technology which could end up in landfill. some(prenominal) companies now cycle these by selling reconditioned devices to other countries or freighternibalising the parts to be utilize again. Websites corresponding Google use huge server-farms around the world. These buildings are full of computers l renderer 24/7.There is an impact on the environment from the huge tot of electrical energy mandatory to run these server-farms. Technology en commensu charge per units us to do human racey things. entirely when are they always middlingly? Googles Street View caused brawl when it was launched after people said that winning photos of their houses was an invasion of privacy. Social communicateing sites, like Facebook, dedicate desexualise it easier to packet information but begin made it difficult to knack privacy settings. You buns now be introduce development GPS technology and Facebook casts Is this the Big Brother state? 5 Computer SoftwareYou need to be able to (a) explain the need for the following functions of an operational system user interface, store management, peripheral management, multi-tasking and pledge (b) describe the purpose and use of harsh utility programs for computer security (antivirus, spyware protection and firewalls), record organisation (formatting, point cabinet steer, and defragmentation), and system maintenance (system information and diagnosis, system kill tools, automatic updating) (c) discuss the relative merits of custom-made indite, off the shelf, open reference work and proprietary software package.Operating System functions wareho apply management User interface The OS manages the transfer of data surrounded by the mainframe, pull and main store (e. g. secure drive) The OS provides the user with a way of controlling the functions of the computer without resorting to machine code. It cigarette be graphical (GUI), e. g. Windows or text-based no cabbage (CLI Command Line Interface), e. g. MSDOS. The OS manages the excitant and output devices attached to the computer, including things like keyboard, mice and releaseer. The OS set asides more than one program to be run at once so users cigarette switch defend and forth mingled with applications easily.The OS provides security features to hold prat recover to the system or particular files. Peripheral management Multi-tasking auspices When trying to remember the functions of an Operating System think MUMPS recollection mgt, User interface, Multi-tasking, Peripheral mgt and Security. 6 Utility programs Type Security train Detects and protects the computer against virus threats. Quarantines infected files. Spyware Detects and removes spyware (small protection programs that quietly monitor what you are doing) Firewall Restrict communication in and out of the computer from the applications that are running.Formatting Sets up a adherey drive, memory stick or card into a format that the computer base use to store/retrieve data. The pro cess of formatting erases any data that was previously on the storage medium. bill Transfer Allows movement of files from one locating to another, all topical anestheticly or via memory stick/FTP to another computer. Defragmentation Re-organises the data on the hard drive to improve read/write get to quantify. System info &038 Provides information about the diagnosis system in order to military service with diagnosis of problems. System cleanup Removes temporary files and tools weighes/archives unused files to append free storage space.Automatic Uses the net profit to check the OS updating is up-to-date and applies software patches/fixes as necessary. weapons platform Antivirus Security Security Disk trading operations Disk Operations Disk Operations System Maintenance System Maintenance System Maintenance 7 Software development custom written Developed specifically for a particular organisation. (a. k. a. bespoke/inAdv custom made to impact exact purpose house) Disad v very expensive and need technical expertise to develop. Off-the-shelf Developed by a software company to be sold to the general public. Adv cheaper than developing it yourself and tech be tolerate forthcoming.Disadv inflexible might not do everything you want it to do. Open germ Written by general public for everyone else to use. Source code provided so software washbasin be tweaked. Adv countenances anyone to use/adapt the software to meet their ask, collaborative approach to development which shagful lead to better caliber software. Disadv by making source code available to all, provide fortune for people to take advantage of software installed on users computers compromise security. copyrighted Written by developer and forgeted to be used by others but with trusted restrictions, e. . movet adapt software. Source code is hidden. Adv can allow for different renderings of same software, e. g. educational version with limited functionality or fullfunctionality vers ion costing more. Disadv source code cannot be inspected so may concur spyware or other malicious features within the software. 8 Computer ironware Definition Computer computer hardware refers to the material parts of a computer and related devices. inbred hardware devices include motherboards, hard drives, and labor. External hardware devices include monitors, keyboards, mice, printers, and scanners.The internal hardware parts of a computer are often referred to as components, while external hardware devices are ordinarily called peripherals. Source www. techterms. com Inputs and sidings (Peripherals) You need to be able to understand the need for input and output devices (a) (b) describe sui send screening input devices for a wide lead of computer controlled situations (c) describe sui confuse output devices for a wide bleed of computer controlled situations discuss input and output devices for users with specific necessarily. (d) Inputs and outputs are the computers wa y of communicating with us the user.Without inputs or outputs our system would be quite limited. Imagine a calculator which didnt allow you to type in summates pool or display the answer on the screen Here are some of the rough-cut input devices used Keyboard The keyboard, along with the mouse, is one of the almost used input devices. Once you get the hang of where the keys are, it allows people to bow textbased data cursorily into the computer. A numerical keypad (found on most keyboards on the right) provides a fast way for accountants and people who work in finance to enter nume commits. 9 There are some elicit variations on the keyboardRoll-up keyboard ( take-away can be rolled up and stuffed in laptop bag) Wireless keyboard (no need for messy wires, frees up user needing to be near computer) Laser Projection (projects a keyboard layout on to any surface sensors detect which keys have been pressed) Mouse The computer mouse is another common input device. It allows the u ser to interact with the software on screen. The mouse is quite versatile, with at to the lowest degree two buttons and the ability to move in any subscribe toion. However, it can be difficult to be precise e. g. drawing use the mouse is quite hard Mice have also undergone a few changes over the years as wellLaptop touchpad (touch-sensitive pads that allow the mouse to be controlled by just a finger) Trackball (the user moves the pointer on-screen by woful rolling the ball the unit doesnt move around like the mouse) optical Mouse (old mice used balls which used to get clogged with diddly-squat and grease new mice use small cameras to detect movement instead). 10 Other Input Devices Scanner Scanners switch somatogenic documents and photos into digital format. They can be used in conjunction with supernumerary software to mechanically read handwriting and convert it into computer text. This is called Optical Character Recognition.Some tickbox forms are scanned in, like the C ensus form or your multiple choice acquirement exams this is called Optical Mark Recognition. Touchscreen Touchscreens have been around for years in one form or another. The latest versions, like the Apple ipad interface use multi-touch technology to allow greater control. Microphone Microphones convert analogue sounds into a digital format that the computer can understand and play vertebral column. Sounds are commonly recorded as . wav or . mp3 files (the latter uses compression to make the file coat small and is more likely to be used to store music tracks).Digital Camera Digital cameras convert live assures into digital format. Photos are usually stored as JPEG files. The grapheme and size of the picture is determined by the trope of megapixels the camera is capable of detecting, e. g. photos taken with an 8 megapixel camera are made up of 8 million pixels. 11 Webcam Webcams capture live television system feeds and apply appropriate software can thus lend those acros s a communicate. Sensors Sensors measure the physical world and translate that into a digital format that a computer can understand. There are various sensors that detect ll manner of things movement, light, heat, moisture, gases (e. g. carbon monoxide levels), location (GPS), etc. For example, the iPhone has an accelerometer so it knows which way round it is to ensure the screen is rotated the correct way. Output Devices Printer Printers produce physical documents and photos from digital files. Most photo effect is done by inkjet printers which can be expensive to run. Laser printers use toner cartridges which are more expensive initially but can print more varlets in front being re go downd. 12 Monitor/screen Monitors/screens provide the visual output from the computer system.Most computer monitors and mobile phones use food coloring LCD (liquid crystal display). Speakers induceing the opposite way to the microphone input, the speaker unit converts digital sound into analogu e strays. 3D Printer A 3D printer uses lasers and a special kind of plastic to build physical 3D shapes from drawings made exploitation CAD software (computer aided design). The aim is built up layer by layer. The unhurt process can take some hours before the final product is finished. They are often used for creating prototypes in manufacturing, e. g. Dyson uses them to create prototype parts for their products.They are legato very expensive but the price is coming down. Motor A motor can be driven with precision by a computer system. Often used in manufacturing, e. g. building cars, motors are used to control robotic arms. 13 Input and output devices for specific needs Keyboards have been adapted for users with limited movement in their arms/hands. A keyboard knowing to minimise the movement of your hands. Trackballs have also been used where users only have limited motor ability. They can be used by hands or feet, like the one below A foot-operated mouse, i take away for people with limited/no mobility in their arms.For quadriplegic users, there are two alternatives to using the mouse or keyboard. The first is voice-recognition this involves the user reading a career of text from the screen so the computer learns their voice pattern. They can consequently use special software to control the computer using voice commands. The technology is getting better but can take over make mistakes. The second is pith-tracking which uses small cameras mounted on the monitor to detect eye movement and move the cursor to the point where the user is gazing. A mouse click is made by blinking silently.Stephen Hawking uses a special device to allow him to communicate. An infra-red sensor detects twitches in the cheek muscle below his eyes in order to enter words and consequentlyce his device generates a computer synthesised voice to read them out loud. 14 Internal Hardware Devices (Components) Central Processing Unit (CPU) You need to be able to (a) state the pu rpose of the CPU (b) describe the function of the CPU as expressing and executing instructions stored in memory (c) explain how common geniusistics of CPUs such as clock speed, cache size and number of cores imply their work outance.The purpose of the CPU is to make and Execute instructions stored in memory. It acts as the brain of the computer and controls the rest of the system. INPUTS and OUTPUTS CPU RAM 15 Fetch Execute Cycle (using Little Man Computer) Download the software http//www. cs. ru. nl/erikpoll/ 3/lmc. Allows you to quit out of the current program and go back to the perish This displays which material body of the fetch/execute cycle we are currently in. The program that is currently being carried out. The current instruction is the one in line with the phase display. Provides the name of the current instruction, along with its op code and operand.This explains what the little man is doing at all(prenominal)(prenominal) stage as he follows the program. Fetch p hase Before the little man can carry out an instruction, he needs to find out which instruction he has to carry out. He does this by first getting the respect from the program takings (The thing that looks like a green mushroom in a shove of wood), and then fetching the value from the corresponding spoken language in memory. The Program Counter The little man uses the value in the program counter to decide which care for in memory he should get the neighboring instruction from.After getting the value, but before going and getting that instruction, he increments the program counter, so that it has the correct value in it when he visits it succeeding(prenominal) time. Memory Memory can be used to store programs, and data. In the fetch phase of the fetch execute cycle we are only interested in the fact that we can get instructions from the memory. 16 Execute phase Once the little man knows which instruction he is going to perform, he has to set about actually doing it. This is t he Execute phase of the fetch execute cycle. For each instruction the little man will perform a serial publication of tasks.For good example, for an input instruction, the little man will go to the input tray, take the value he finds there, and go and put it into the calculator. For an add instruction, he will take a value from memory, and add it to the value presendly in the calculator. Once the execute phase is complete, the little man will start up the cycle again, and well to the program counter to get the value of the following instruction he has to fetch. The Input and Output trays These are what we (the user) use to communicate with the little man. We provide him with data via the input tray, and when hes ready, he provides us with data via the output tray.Calculator (Arithmetic Logic Unit ALU) On a real computer, this would be the Arithmetic Logic Unit (ALU). Its basically a calculator that will carry out arithmetic operations. Memory Memory is accessed during the exec ute phase when we need to store or access data. It is likely to overwrite your programs when putting data into memory though, so be thorough where you put it. Following a program (Decoding instructions) The program is a series of instructions made up of an op code and operand (either data or the address where data is stored).For example Op code Operand 1 2 3 4 5 6 7 800 801 802 9 Load livestock convey Subtract Input Output Halt leap If Negative Skip If Zero Skip If Positive Jump 2 means Store 2 99 99 refers to the memory address where little man should store the data. These can be stored as binary program star molybdenum patterns, e. g. 10 could refer to the op code (2) preceding(prenominal) and 11000011 could refer to the memory address (99). mobilize 2 in binary is 10 and 99 is 11000011. This would give the second gear pattern for the above instruction as 1011000011 Q. How does little man (CPU) know the battle amongst data or an instruction?It all depends on which ph ase of the cycle the CPU is in, e. g. in the Fetch phase the CPU knows it is an instruction. In the Execute phase the CPU knows it is data. Op codes understood by LMC 17 Characteristics which affect performance Clock Speed This is the number of cycles that the CPU can complete in one second ( thrifty in Hertz or Hz) A prompt clock speed means the CPU can process more instructions per second. For example a 1MHz processor can process 1 million instructions a second whereas a 1GHz processor can do 1000 million instructions in the same time.This is the A big cache size means prop knowledge domain for more data can be held and data from the its less likely that any cycles are wasted. A RAM. It ensures the CPU smaller cache size and is always slewy fast clock speed may with data. result in a bottleneck between the RAM and CPU. A dual-core processor or This is the quad-core processor is 2 number of impact cores to 4 times faster than a conventional chip as they the CPU has. A can pro cess simultaneous dual-core has instructions. two and is able to process two instructions simultaneously in the same cycle. amass sizeNumber of Cores It is important to balance all of the above to avoid over-speccing one area and creating bottlenecks elsewhere. 18 Memory You need to be able to (a) describe the difference between RAM and ROM (b) explain the need for ROM in a computer system (c) describe the purpose of RAM in a computer system (d) explain how the amount of RAM in a personal computer affects the performance of the computer (e) explain the need for virtual memory (f) describe cache memory (g) describe winkle out memory (h) discuss how changes in memory technologies are leading to innovative computer designs.RAM and ROM Both are needed in a computer system but for different reasons. In a computer computer, ROM (Read Only Memory) is used to store all the instructions (the BIOS raw material Input/Output System) to get the computer up and running. It seeks out the amou nt of memory, input and outputs available to it and then loads up the operating(a) system. In some computer systems, like your washing machine, the ROM stores the software to control the hardware, as well as data such as planning/washing times etc.RAM (Random admission price Memory) is used as temporary storage for instructions and data between the inputs, outputs, unessential storage (e. g. hard drive) and CPU. The larger the RAM, the more instructions/data can be held in quick access memory without needing to use realistic memory this can improve performance. Random Access Memory Read Only Memory vaporific (forgets everything when power switched off) Non-volatile (remembers content even if power switched off) Can be written to and read from Can only be read from (not written to) unremarkably measured in Gigabytes (Gb) For the BIOS, usually measured in Kilobytes (Kb) 9 Virtual Memory Depending on the size of the RAM, it is not always possible to store all the running programs in the RAM at once and the computer will start running low on memory and slow down. This is where virtual memory comes in. It stores the data that the RAM isnt actively using on the hard drive to free up the RAM. wherefore, when the CPU needs the data it pulls it back from the virtual memory on the hard drive. As far as the CPU is concerned, all the programs are running from the RAM. The operating system sets up a paginate file on the hard drive to be used for virtual memory.This is usually set at twice the size of the amount of RAM, e. g. 1GB of RAM should have a 2GB varlet file. Cache Memory This has been explained in the CPU section on page 17. pullulate Memory Flash Memory is often referred to as solidity storage, which means that there are no moving parts. Its mistakable to RAM but is non-volatile which means when the power is cut off, it still remembers the content). Flash memory is used in USB memory sticks and memory cards for digital cameras and some games consoles, e . g. Sony PSP.Future developments in Memory technologies Physical Size &038 Capacity cost Speed Power Memory chips have become more fatheaded (storing more compositions per chip) which has lead to smaller computing devices and larger capacities. The cost of memory has fallen which means it is now affordable to have large amounts of RAM available. Read/write times are improving which mean faster access and better performance. Memory chips are more power-efficient meaning portable devices work for longer between charges and batteries can be smaller and lighter. 20 Secondary StorageYou need to be able to (a) explain the need for secondary storage (b) describe common storage technologies such as optical, magnetized and solid state (c) select suitable storage devices and storage media for a given application and justify their choice using characteristics such as capacity, speed, portability, durability and reliability. Secondary storage is needed for when we want to store files perman ently or semi-permanently. We might want to transfer files between computers by using portable secondary storage media. Storage TechnologiesCodes data using microscopical dips on the surface of the disc. Units Optical Codes data using small changes in magnetic fields. magnetised Uses non-volatile memory chips to store bits of data Solid put up Candidates should be able to (a) define the terms bit, assemble, byte, kilobyte, megabyte, gigabyte, terabyte Bit 1 Nibble 4 bits Byte 8 bits Kilobyte (Kb) 1,024 bytes Megabyte (Mb) 1,024 kilobytes Gigabyte (Gb) 1,024 megabytes tuberculosis (Tb) 1,024 gigabytes 21 Storage Media Comparison Storage Medium CD regularity Optical Capacity Medium 650-700Mb Small 1. 4Mb Large 1Gb to 2+ Tb Speed Fast access Portability Lightweight and prone Lightweight and flat Heavy and not designed to be carried around. Requires integrating into computer system. Medium-weight. Plugs into computer USB or Firewire port. Lightweight and small. Durability and Reli ability slowly scratched and will then not work. Can only be written to once. Can be snapped. Can be damaged by strong magnets or heat. sooner reliable but can crash when the read/write head crashes into the platter. Sometimes happens on laptops when dropped. Can be damaged by magnets.Same concerns as internal hard drive. Floppy Disk Magnetic Slow access Internal Hard Disk Magnetic Fast access (dependent on speed of motor RPM rotations per minute) Portable Hard Disk Magnetic Large 40Gb to 640Gb Medium-fast access (dependent on connection method, e. g. USB cable) Flash drive (USB stick or memory card) Blu-ray disc DVD (Digital Versatile Disc) Solidstate Optical Optical Medium/Larg Medium-fast access e (dependent on connection 1Gb to 64Gb method, e. g. USB cable or card reader) Large Fast access 50Gb Large Fast access 4. 7Gb non affected by magnets.Quite hardy. Can be dropped without damaging contents. Easily scratched and will then not work. Easily scratched and will then not wor k. Lightweight and flat. Lightweight and flat. 22 binary Logic You need to be able to (a) explain why data is be in computer systems in binary form (b) understand and produce simple-minded logical system diagrams using the operations NOT, AND and OR (c) produce a truth table from a given logic diagram. Computers use binary as its a lot simpler. Each CPU is made up of millions of transistors which can only have two states (ON/OFF).Anything can be converted into a binary number so a computer can understand, process and store it. NOT Gate NOT Truth Table Input Output 0 1 1 0 Flips the input, e. g. 0 becomes 1 and 1 becomes 0. AND Gate a b Waits for 1 on both inputs before outputting a 1. AND Truth Table Input Input Output a b 0 0 0 0 1 0 1 0 0 1 1 1 OR Gate a b Wait for 1 on either input before outputting a 1. OR Truth Table Input Input Output a b 0 0 0 0 1 1 1 0 1 1 1 1 You can practice with NOT, AND and OR gates using the following website http//logic. ly/demo/ 23 Representation o f data in computer systems verse pool You need to be able to (a) convert positive denary whole amount (0-255) into 8-bit binary numbers and vice versa (b) add two 8-bit binary integers and explain overflow errors which may occur (c) convert positive denary whole numbers (0-255) into 2-digit hexadecimal numbers and vice versa (d) convert between binary and hexadecimal equivalents of the same number (e) explain the use of hexadecimal numbers to correct binary numbers. denary and Binary conversions Numbers greater than 1 can be map outed in binary by using more bits. e. g. 129 can be represented in 8 bit (byte) binary as 10000001. tenfold Binary 128 1 64 0 32 0 16 0 8 0 4 0 2 0 1 1 This means that if you put a 1 on each increased by bifurcate bit (i. e. 11111111) the highest denary for each new bit added to the left. number 8 bits (a byte) can store is 255 128+64+32+16+8+4+2+1 = 255. Notice how the number To convert binary into denary, just add together the denary numbers above ea ch bit that has 1 in it, e. g. 10000001 = 128 + 1 = 129. To convert a denary number into binary, find the highest value that will go into it and then continue down the number of bits with the remainder until there is nothing remaining. 4 For example, to convert 44 into binary 8-bit format 44 is smaller than 128 and 64 so we place 0s in those bits Denary Binary 128 0 64 0 32 does go into 44 with remainder of 12, so we place a 1 in that bit Denary Binary 128 0 64 0 32 1 The remainder of 12 is smaller than 16 so we place a 0 in that bit Denary Binary 128 0 64 0 32 1 16 0 8 does go into 12 with remainder of 4, so we place a 1 in that bit Denary Binary 128 0 64 0 32 1 16 0 8 1 4 does go into 4 with with nothing remaining, so we place a 1 in that bit Denary Binary 128 0 64 0 32 1 16 0 8 1 4 1 nd 0s in all the remaining bits Denary Binary 128 0 64 0 32 1 16 0 8 1 4 1 2 0 1 0 Therefore 44 as an 8-bit binary number is 00101100. 25 Adding two binary numbers together Adding two binary numbers together is not as scary as it sounds or looks. It uses the same principles at the denary number system (Hundreds, Tens, Units). For example Work from right to left, like you do when adding denary numbers using HTUs. 00010010 + 00010100 0+0=0 0+0=0 0+0+1 1+1=0 0+0=0 0 0 11 0 0 1 1 0 0+0=0 1+0=1 0+1=1 (carried over) = 1 (carry 1)Lets convert it back into denary to check it is correct Denary 128 Binary 0 16 + 2 = 18 Denary 128 Binary 0 16 + 4 = 20 Denary 128 Binary 0 32 + 4 + 2 = 38 64 0 32 0 16 1 8 0 4 0 2 1 1 0 64 0 32 0 16 1 8 0 4 1 2 0 1 0 64 0 32 1 16 0 8 0 4 1 2 1 1 0 So as 18 + 20 are 38. Then we know the binary calculation is correct 26 Hexadecimal Numbers Programmers started to use hexadecimal to reduce mistakes and make it easier for them to understand than using a lot of 0s and 1s. Denary and hexadecimal conversions Hexadecimal uses a base 16 system = 0-9 and then A-F.That means that the denary number 15 is gibe to F in hexadecimal. The denary number 16 is equal to 10 in hexadecimal (which means 1 lot of 16) The highest denary number represented in 8-bit (byte) binary is 255 and was represented by 11111111. In hexadecimal this would be represented as FF (15 lots of 16 + 15). Confused? Remember, F in hexadecimal represents 15. Therefore F0 would be 15*15=240. The second F is 15, therefore FF = 240+15 = 255. To convert denary to hexadecimal you can single out the number by 16. For example, to convert 141 into hexadecimal do the following 141 / 16 = 8 remainder 13. /16 = 0 remainder 8. Therefore, working from right to left, the hexadecimal number is 8 13 (and 13 is represented as D in hex) so it would be 8D. Alternatively, convert the denary number into binary and then binary to hexadecimal. 27 Binary to hexadecimal conversions To convert binary to hexadecimal you need to break it down into nibbles (blocks of 4 bits). For example, 141 as a binary number is 10001101. The two nibbles are 1000 and 1101. Converting each nibble into denary we can see that 1000 = 8 and 1101 = 13.Remembering that 13 = D in hexadecimal then 141 would be represented as 8D. To convert hexadecimal to binary you just reverse the process. Convert each part of the hexadecimal number into nibbles of binary numbers. For example Hex Denary Binary 8 8 1 4 0 nibble D 2 0 1 0 8 1 4 1 nibble 2 0 1 1 HELP This conversion chart below may help to make sense of it all Denary 0 1 2 3 4 5 6 7 Binary 0000 0001 0010 0011 0100 0101 0110 0111 Hexadecimal 0 1 2 3 4 5 6 7 Denary 8 9 10 11 12 13 14 15 Binary 1000 1001 1010 1011 1100 1101 1110 1111 Hexadecimal 8 9 A B C D E F 8 Using binary to represent characters You need to be able to (a) explain the use of binary codes to represent characters (b) explain the term character set (c) describe with examples (for example ASCII and Unicode) the relationship between the number of bits per character in a character set and the number of characters which can be represented. Computers use the ASCII (American Standard Code for Information Interchange) format to use binary codes to represent numbers, letters and special characters. It uses 8-bits (byte) to represent each character, so every character has its own incomparable 8-bit ASCII code.Using the ASCII character set on the next page we can convert characters into binary numbers. For example, Isambard would be represented in binary as I s a m b a r d = = = = = = = = 73 115 97 109 98 97 114 100 = = = = = = = = 0100 1001 0111 0011 0110 0001 0110 1101 0110 0010 0110 0001 0111 0010 0110 0100 Notice how the capital I is different from the little i in the ASCII format. An upper and lower case version of each letter is present in the chart to enable the computer to rank the difference between them. If you remember what we said about binary numbers back on page 23 then you know that 8-bits (a byte) can store up to 255 in denary.This means that the ASCII format can have up to 255 characters represented in a character set. 29 American Standard Code for Information Inter change character set mention You dont need to remember these codes for your exam but just be aware of how it works. 30 Using binary to represent juts You need to be able to (a) explain the representation of an image as a series of pixels represented in binary (b) explain the need for metadata to be included in the file such as upper side, width and tint depth (c) discuss the effect of colourise depth and village n the size of an image file. Images on the computer are made up of lots of individual pixels (small squares of colour). If you zoom into any image enough times you will see these little blocks of colour. We can use binary numbers to represent each pixel. In a simple image, where there are only two colors (colour depth of 1) then we can just now use a 1 for one colour, and 0 for another. For example, look at this small 3 x 3 pixel image below. The 1s represent the black colour and the 0s represent the white. 0 0 0 1 0 0 0 1 31 That is the principle bed storing images as binary. However, we also need to know a few other things about the image in order to display it correctly, i. e. its height, width and colour depth. Image Metadata Height Width Colour depth Resolution The height of the image in pixels The width of the image in pixels The number of bits available to represent each pixel The pixels per inch (PPI) if the pixels per inch is high, then the resolution and image quality is also high.Without this metadata the computer would not be able to reconstruct the image properly. Colour Depth In a simple 1-bit colour depth image, we can only display two colours. However, in an 8-bit colour depth image (like the gif format), we can display 256 colours (one for each binary number from 00000000 to 11111111). In a 24-bit colour depth image (like the jpeg format), we can display just over 16 million colours If we use more bits to store each pixel, then the file size will be larger. That is why . gif images are often smaller in file size than . peg ima ges. Resolution If the image has a higher(prenominal) resolution, it has more pixels to store data about and is therefore larger in size. If the image is lower resolution, this means that there are less pixels per inch, which means less pixels to store data about and is therefore smaller in size. 32 Using binary to represent sound You need to be able to (a) explain how sound can be sampled and stored in digital form (b) explain how sampling intervals and other considerations affect the size of a sound file and the quality of its playback.Sound is stored in the computer by taking samples of the sound wave at regular intervals and converting those into binary numbers (using an analogue-to-digital convertor). The computer can then re-create the sound by reversing the process. The file size and quality of the sound recording is affected by the sample rate and bit rate. The sample rate refers to the number of samples taken each second. It is measured in Hertz (like the CPU clock speed). If the sound wave is not sampled at a higher enough rate, this can lower the quality of the sound recording, but the file size would be smaller.If the sound wave is sampled at a higher sampling rate, this will increase the quality of the recording, but the file size will be much larger. The bit rate refers to the amount of bits used to store the different levels of sound at each sampling interval. The more bits, the greater range of levels that can be distinguished. This also has the affect of increasing the file size if the bit rate is high (e,g. 16-bit instead of 8-bit). 33 Computer Communications and NetworksNetworks You need to be able to (a) explain the advantages of lucreing stand-alone computers into a local area vane (b) describe the hardware needed to connect stand-alone computers into a local area intercommunicate, including hub/switches, radio receiver access points (c) explain the different roles of computers in a client-server and a peer-to-peer engagement (d) descri be, using diagrams or otherwise, the ring, pile and star profits topologies (e) describe the differences between a local area network and a wide area network such as the Internet explain the terms IP addressing, MAC addressing, packet and (f) protocols (g) explain the need for security measures in networks, such as user access levels, suitable passwords and encryption techniques (h) describe and justify network policies such as acceptable use, disaster convalescence, failover, back up, archiving. Why network? Allows computers to communicate with each other and divvy up resources, e. g. peripherals (printers, scanners), storage, internet access. Data Packets Information is sent around a network in data packets. Data is broken down into packets to be sent over the network and often may take different routes to get there. It contains info on where it needs to go (the address) and the packet number and an error-checking knack to ensure the packet arrives intact and can be put back together in the right order. 34Basic components of a local area network (LAN) Client/ Computer Hub, Switch or Router See next page for explanation of each. Server In a Client-Server network, the server handles the logins, applications and file storage. Modem Interfaces between the Internet and the network. Shared Peripherals Networks allow peripherals like this printer to be divided by all the computers on the network. Internet 35 Hub, Switch or Router? These are not the same. You need to know the difference between them. Hub A hub receives all data sent over the network and sends it to all the other devices on the network. Only the device who the data packet is for will concede it the other devices will ignore it.A switch is bit more tidy than a hub and it learns which devices are on the network (and their port number/address) and only sends the data packet to the computer who is the intended recipient. This is more efficient than a hub as it doesnt result in lots of unnecessar y network traffic. A router is cleverer still than both hubs and switches. It can re-direct network traffic and deal with different packets in different ways. It can protect the computers on the network by hiding them from the outside world (i. e. a firewall). Some routers have a modem built-in and wireless capabilities. Most homes have a 4-port wireless broadband router to access the Internet. This combines the router and modem functions. Switch RouterWireless access points dont require a physical connection and therefore are suited for a variety of different devices and provide access to network over an area, e. g. iPad or smartphone. IP address The IP address (Internet communications protocol) is a computers unique address on the network, e. g. 192. 168. 0. 1 is usually your home routers address. On the Internet, each website has its own or some(prenominal) IP addresses. 36 MAC address The MAC address (Media Access Control) is a hexadecimal number that is unique to that particul ar device. Hey Did you know that there are 281,474,976,710,656 possible MAC addresses in the world? Thats a lot of MACs baby huh huh Network Protocols Protocols are a set of standards and guidelines that tell computers how they should handle the sending and receiving of data over the network.TCP/IP (Transmission Control Protocol and Internet Protocol) apply to exchanged data between computers on a network and route packets between networks and over the Internet. apply on web to transfer webpages and web content from the website host server to the computer beging the page. utilize to transfer files between computers over a network. Used to transport emails. HTTP (HyperText transfer Protocol) FTP (File Transfer protocol) SMTP (Simple Mail Transport Protocol) LAN or crazy? A LAN is a Local Area Network which is usually set-up within a certain area, e. g. a building or sort out of buildings hence the term local. A WAN is a gigantic Area Network which is usually on a nationwide or worldwide scale. The Internet is an example of a WAN a series of inter attached LANs. 7 Network Topologies A network can be set up in three main ways sinker 4 3 5 1 2 All the computers are linked together in a ring and data packets are sent one way round. For example in the diagram above to get from PC 1 to PC 5 the data needs to go through PCs 2, 3 and 4. It cant go anti-clockwise back to PC 5. Drawbacks If there is one break in the ring then the network breaks down. Also not very efficient as a lot of network traffic doesnt take the most direct route. Bus All the computers are connected to a central mess. You can add and take away computers easily in a double-decker network as the computers are connected to the central bus, rather than between one another.Drawbacks Only one computer can use the bus at once which means only one computer can communicate at a time the others have to wait until the bus is free before sending their data this makes it slow. If a computer connect ed to the bus breaks down, then the network still runs but if the central bus breaks down then so does the whole network. 38 Star 4 3 5 1 2 All the computers are connected to central server. The server can handle multiple communications at once and re-directs traffic over the network. More computers can be added or taken away without affecting the network. Drawbacks If the main server fails then the network goes down. Client-server and peer-to-peer networks In a Client-server network, the server acts as the main computer intervention login requests, user storage, etc.The client could be any computer. The user can log on to any client and still access their stuff on the server. In a Peer-to-peer network, each computer shares information equally and plays an equal role in the network. Network Security Part of Data Protection Act 1998 requires companies who store data electronically to restrict it riskless and secure. Without security then anyone could hack into the network and inte rcept data packets. Confidential data packets should be encrypted so if they are intercepted they are unreadable. There may be a need to pr causa unauthorised access to particular areas of the system this could be controlled by passwords and different user levels, e. g. n the school a student can only access the student shared drive, whereas teachers can access both the student shared drive and the staff shared drive. 39 Network Management Policies Disaster recovery In the event of the system failing there needs to be plans in place to get the network up and running again as quickly as possible. Many organisations, such as banks, have a disaster recovery plan which may mean relocating to a different location (if the building is no longer accessible). Failover and backups If there is a power cut, many networks have UPS (uninterrupted power supplies) which are large batteries with enough charge to keep the network going long enough to shut it down correctly. If a hard drive fails, the re is usually a backup which can take the strain.Networks are often backed up at least daily and these backups are stored off-site or in a fire-proof safe so in the event of a disaster in the building, the data is still intact. Maintenance Sometimes data needs to be unbroken but is not accessed regularly. This data can be archived off onto tape measure to help free up space on the network. Acceptable Use It is important for the network to have an acceptable usage policy to provide users with guidelines about what they can and cant do using it. For example, it would use up vital network bandwidth if some users decided to play a network game or download the latest torrent from the Internet. If users start file sharing copyrighted materials, like music, using the network then there is a legal issue to consider as well. 40 The InternetYou need to be able to (a) describe the nature of the Internet as a worldwide collection of computer networks (b) describe the hardware needed to connect to the Internet including modems, routers etc (c) explain the need for IP addressing of resources on the Internet and how this can be facilitated by the role of DNS servers (d) explain the importance of hypertext mark-up language and its derivatives as a standard for the creation of web pages (e) describe common file standards associated with the Internet such as JPG, GIF, PDF, MP3, MPEG (f) explain the importance of compress files that are transmitted via the Internet (g) describe the differences between lossy and lossless compression. What happens when you type in a web address in your web browser? When you enter a web address in your browser, it heads off via your modem to your ISPs (Internet Service Provider) domain name servers (DNS).These computers store the IP address(es) for each website and directs your request to the relevant server hosting the webpage you want to view. The information is then sent back to your ISP and then back to your computer. Why HTML? HTML (HyperTe xt Markup Language) provides a standard format which any computer with web browser can view and display the pages. It allowed the World Wide Web to get going as there was a universal standard that everyone could now use to share information. 41 Common file formats used on the Internet . hypertext markup language . jpg HTML Web page JPEG image Used to store webpages Used to store photos as can show up to 16. 7 million colours. Used for simple graphics and short animations can show up to 256 colours.Used to store noneditable documents for viewing on the Internet using the free adobe viewer software. Used to store music tracks. Compressed to make downloading faster. Used to store videos. Compressed to make downloading faster. Used for Adobe Flash files to add interaction and/or animations to websites. Used to store video files playable using free Apple viewer software. .gif Graphic Interchange format image .pdf Adobe Portable Document format .mp3 MP3 Music format .mpg MPEG video for mat .swf Shockwave Flash format .mov Apple Quicktime format Why compress on the Internet? The Internet can be slow at times, especially in its premature days relying on early 56Kbps modems as opposed to the 3-4 Mbps average.Therefore if you could compress the files that were being sent on the Internet, then you sent smaller files, and smaller file sizes meant faster downloads. It also frees up the network and avoids clogging up the bandwidth. 42 Lossless versus Lossy coalition Lossless compression Compression used means the original file stays completely intact and unchanged. Used for text documents, data files and practicable programs where it would not be desirable for parts to be lost. Used for multimedia system files, i. e. sound, images, video. Lossy compression Compression which involves discarding parts of the file which wont be noticed if they are not present.For example, it is possible to remove some data within an image and your brain fills in the gaps. Take a look at the images of the dog below Source wikipedia. org The image has more compression applied to it as you go from left to right. Even though the image on the right in heavily compressed, we can still see it is a dog. Our brain fills in the gaps. 43 Databases What is a database? A database is a persistent organised store of data which can be easily and quickly searched. They are most commonly used for Marketing, e. g. fealty cards. Huge databases are searched for patterns in customers buying habits and then targeted coupons are mail shot to customers.The school has several databases to store everything from your demeanor logs and Brunels, to your address, date of birth and even how much money you have on your lunch card Data handling software, such as Microsoft Access, allow users to add tables, define fields and validation (create) add/edit/ remove data (maintain) run queries to extract information from the database (interrogate) DBMS (Database Management System) Many large databases use a database management system (DBMS). This system separates the data stored from the data handling applications used to maintain and interrogate the database. Feature cooccurring usage Security Recovery &038 Backup Data integrity Why is this good? Allows multiple users to use the database at the same time Provides bility to allow/restrict data access to individuals or applications Provides backup solution and recovery tools to ensure data is not lost in event of stroke Enforcing data integrity by ensuring data is consistent and adheres to the rules Relational databases A flat-file database is when all of the data and fields are stored in one table, e. g. an stand out spreadsheet full of names and addresses see below 44 A comparative database is when that data is separated into individual tables (entities) that are linked by a primary key (which appears in each table). Student Student ID first-year name Surname Class Class ID Student ID teacher ID Teacher Teacher ID discove r SubjectIn the example above, the STUDENT, CLASS and teacher are all tables (entities) in the database. The id is the unique piece of information (the primary key) that identifies each instance of a student, class or teacher. We couldnt use First Name as the primary key in STUDENT as many people share the same first name it isnt unique enough The advantage of separating the data into different entities is to avoid data tautology when the same data is stored in several places in the database. Lets imagine if we stored the information above in a flat-file database (all in one table) it would look something like this Duplicated data Can you see the duplicated information?Not only does this use up space but it is easier to make a mistake (and lose data integrity) if we only update one of the records. E. g. if get out Parsons gets married and her name changes to Mrs Smith then we need to make this change for every record in the database. If are using a comparative database, becaus e the Teachers name is stored in a separate table and linked to the rest of the entities, we only need to update it in the TEACHER table once. In the CLASS entity, both Teacher ID and Student ID are foreign keys (primary keys that when linked to another table become foreign keys in that table). Components of a relational database Tables Represents the entity in the database. Fields and primary keys are defined and data stored in the table. Create) Forms Provide a customisable user interface to add/edit and delete data (Maintain) Queries Allow data that meets specific criteria to be extracted and displayed (Interrogate) Reports Displays the results of queries in a customised format designed to be printed Querying a database 45 When interrogating a database, you need to specify the fields you wish to display and the touchstone you will use to search. E. g. if you were searching for a car on a car supermarket website you might search using the make of the car you cherished Make = Fo rd You could also use logical operators such as (NOT equal to), < (less than), > (greater than), = (greater than or equal to). E. g. Mileage