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125 Cards in this Set
- Front
- Back
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Motherboard
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The main printed circuit board in the computer with sockets to connect the other parts
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Hardware
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The physical parts that make up the computer
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ROM
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Read only memory. ROM is non-volatile as it needs to obtain instructions the moment the computer is switched on as it stores the BIOS: Basic input output system which is used to start the computer. It also allows to check the type of hard disk installed, amount of RAM installed and type of CPU used etc.
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RAM
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Random Access Memory. Whereas RAM is volatile; it stores the data you are currently working on as well as the modules needed for the applications to work so you can have multiple windows open at the same time.
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Describe the importance of computer systems in the modern world
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Makes work easier and faster
Confidential files can be password protected We are becoming increasingly dependent. |
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Explain the need for reliability in computer systems
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As we become more dependent our need for security also increases. E.g. Banks, to withdraw money you need the system to be reliable so that it will give you the correct amount or make sure that someone else can't access your account.
There are also health and safety implications if computer systems go down e.g. in hospitals, the reliability of a life support machine is crucial, its literally life or death. Computer controlled motorway signs could also cause chaos if they were to break down. |
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How can you measure reliability?
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Availability is how long the system is available for, usually quoted by average availability over a long period of time.
MTBF (mean time between failure) is quoted by equipment manufactures as an indication of reliability. It's the average number of hours that the system runs for before something breaks (tends to be a measure of hardware) |
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What are some measures to protect against system failures?
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Hardware redundancy. Having more than one of a critical component. Redundant hardware companies have to make sure that data is backed up regularly.
Disaster recovery plan are sometimes put into place so a company can switch over to a completely new system with all their own data on it, often within hours; useful if you depend on your computer system. |
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Why is it important to use software development standards when developing a new computer system?
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So the system developed can:
Work in teams to develop the system as they all have a common understanding of the design tools and diagrams Move between companies as the standards apply across the industry Pick up someone else's design and code the program to achieve it Maintain somebody else's program when the customer's requirements change |
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What is the Waterfall Development Method?
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A software development method that breaks the project down into a series of timed steps, some of which can overlap.
including: define requirements, analyse, design, implement, test ( verification), installation, maintenance. |
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What is Rapid Application Development?
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A software development method that starts with a prototype that is developed gradually into a full solution with customer feedback at each stage and with the help of tools like GUI interface builder and CASE tools (computer aided software engineering). These tools need a lot of training and aren't cheap.
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Why are there standards?
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To help with change control and maintenance.
To help with the development phase. |
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What is the data protection act?
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Anyone who stores personal details must keep them secure. To meet this requirement the system should have security mechanisms designed into it.
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What is the Health and Safety at Work Act?
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Employers are responsible for their staff. Design considerations should provide appropriate working conditions for staff e.e how easy systems will be to use and any health implications there might be based on their choices of software, screen layout, input methods and the hardware used.
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What is the Copyright, Designs and Patents Act?
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It is illegal to use software without buying the appropriate licenses. When the system is designed and implemented, licensing must be considered in terms of which software should be used.
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What are the ethical considerations when creating a computer system?
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Fairness. e.g. accessibility for all, where the programming work is done, does is disadvantage some part of the community?
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What are the environmental considerations when creating a computing system?
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Often the carbon footprint and waste products that result from manufacturing computer systems (however this is often outweighed by the positive effects on the environment of using computerised systems to manage processes that might otherwise generate more pollution.
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Why does data need to be converted into a binary format to be processed by a computer?
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Because a computer only has two states, off or on, so everything stored in a computer can be stored as a series of 1s and 0s. (binary)
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Why do you get overflow?
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A computer stores things in memory in a finite amount of space. If you cannot represent the number in that amount of space because it is too big.
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Explain the use of binary codes to represent characters
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Each character on a keyboard has a code number that gets transmitted to the computer when it is typed. The code number is stored in binary. different sets of codes are available for different types of computer.
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Define Character Set
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A group of characters that can be coded. e.g. ASCII is the character set the is used by PCs
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Explain the relationship between the number of bits per character in a character set and the number of characters which can be represented e.g. Ascii and Unicode
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ASCII uses 7 bits to code each character meaning that you can have 128 different characters in the character set (using codes from 0 to 127)
Unicode has a 16-bit encoding system so has 2^16 (65,536) different characters in its character set. |
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Explain the representation of an image as a series of pixels represented in binary
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A photograph on a digital camera stores the image as a broken down version of pixels (short for picture element). Each pixel is one specific colour. an image that is 400 pixels wide by 500 pixels deep, the picture's resolution would be 400x500.
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Explain the need for metadata to be included in the file such as height, width and colour depth
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The computer needs metadata such as the resolution and colour depth in order for it to interpret the file and rebuild the picture.
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discuss the effect of colour depth and resolution on the size of an image file.
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The greater the colour depth the better the colour resolution (the output device must be able to render the colour in the first place though)
The finer the grid (the more horizontal and vertical pixels used) the closer the dots can be, therefore the better quality the picture. |
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What is a bitmap?
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an image file format that represents an image as a series of pixels, each pixel defined by a 24 bit binary number split into 3 bytes for RED, Green and blue.
It contains data for each pixel so bmp files can be very large, (uncompressed) |
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What is lossy compression?
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a format that discards some of the image detail to get even more compression, but does so that it hardly notices the loss of quality (downside to this is that when you edit the image and save again you lose more detail each time. JPEG is a popular lossy method
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What is lossless compression?
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Compresses the image without losing any detail at all. Excellent for long term storage of images (e.g. TIF file format)
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What is sampling?
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Sampling is a method of converting an analogue sound signal into a digital file containing binary numbers.
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Explain how sound can be sampled and stored in digital form.
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Each sample is a regular measurement of the sound wave at a specific instant in time, first by measuring the amplitude of the signal and then converting it into the equivalent binary number. The whole collection of data is then stored in a digital file.
The longer the sound track the larger the file becomes due to the many samples making up the track. |
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What is sampling frequency?
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The rate at which samples are taken. The sample frequency has a great affect on the quality of the recording.
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What is Nyquist sampling frequency?
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The minimum sampling rate is at least twice the highest frequency in the signal. As otherwise the frequency information of the sound will be missed.
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Explain how sampling intervals and other considerations affect the size of a sound file and quality of its playback
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Sound quality is affected by:
Sample Resolution Sample interval |
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What is sound synthesis?
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When the sound is re-created by the computer through speakers form this file.
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`Explain how instructions are coded as bit patterns
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Instructions are converted into machine code, a binary representation (bit patterns) of the instructions you typed.
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Explain how the computer distinguishes between instructions and data
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The computer distinguishes the bits that represent programs and bits that represent data through the operating system as it knows where the data and the programs are located in main memory.
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State the purpose of the CPU
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The CPU is the hardware that executes programs and manages the rest of the hardware.
It fetches instructions and data from main memory, decodes and executes the instructions and performs calculations. It also manages the movement of instructions and data to and from the peripheral devices. |
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Describe the function of the CPU as fetching and executing instructions stored in memory
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For a program to run on a computer it must be loaded into the main memory first and then the CPU uses the start address of where the program is located to fetch an instruction, decode it and then execute it. The processor executes one instruction at a time.
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Explain how common characteristics of CPUs such as clock speed, cache size and number of cores affect their performance.
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The higher the clock speed the more powerful and faster the CPU can operate, runs hotter and consumer more power.
The less often the access to main memory, the faster the processor can work, so the CPU increases. A multiple core processor will work faster than a single (although unless the application is designed to use multiple cores its not necessarily faster) Access speed of the main memory can be increased to increase the processor speed by using faster memory technologies but this increases the price of the computer so you must be able to find a balance. |
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Describe the cache memory
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RAM isn't fast enough to cope with the speed that the CPU needs to deal with data. The cache is a volatile computer memory that can be accessed much faster than RAM.
The CPU looks in the cache, if data is there it will process it, if not there, the CPU accesses system memory and puts a copy of the new data in the cache before processing. Larger the cache size, the better the performance as ore data is able to be stored locally |
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Convert positive denary whole numbers (0‐255) into 8‐bit binary numbers and vice versa
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Put it into the chart
128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 0 | 0 | 0 | 1 | 0 | 1 | 1 | 1 = 23 (get it?) vice versa just minus from the number you want in binary. e.g. for 205 you'd minus 128 (and add a 1) then minus 64 (add a 1) then you'd have 13 so you can't minus 32 (put a 0) etc. Even if the number is 3 which is 11 in binary you'd write the zeros before it so that it is 8-bit as computers usually store data in bytes |
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convert positive denary integers (0‐255) into 2‐digit hexadecimal numbers and vice versa
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Hex is like decimal numbers but counts 1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,10,11,12,13,14,15,16,17,18,19,1A,1B etc. as is counts with denary numbers
e.g. 26 in denary is 1A in Hex. |
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convert between binary and hexadecimal equivalents of the same number
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For Binary to hex cut the binary into 4 bit parts
e.g. 8 | 4 | 2 | 1 | 8 | 4 | 2 | 1 1 | 1 | 1 | 0 | 1 | 0 | 1 | 0 = 14 = 10 (convert to denary) = E = A (convert to hex) and vice versa |
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explain the use of hexadecimal numbers to represent binary numbers
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Humans find it difficult to remember long strings of numbers so instead of remembered binary we convert it into hexidecimal (hex)
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describe the difference between RAM and ROM
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RAM is volatile (all data is lost when the computer is shut down) and read-write. Random Access means that you can write anywhere in that memory space at any time.
ROM is not volatile and as it is Read Only, you cannot write over the contents. The data is permanent. |
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explain the need for ROM in a computer system
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Read Only Memory is used to 'boot' up the computer - it holds the BIOS (basic input output system). It needs to be non-volatile as the computer must be able to obtain instructions (like the configuration settings) as soon as it starts up.
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describe the purpose of RAM in a computer system
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Random Access memory is located in main memory and stores the modules and files of the applications open (main memory is also referred to as the Immediate Access Store or Primary Memory). When the RAM is full the computer performance slows
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explain how the amount of RAM in a personal computer affects the performance of the
computer |
There is only a limited amount of space in the RAM and if it fills up then the computer system crashes unless the operating system deals with it (e.g. virtual memory)
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explain the need for virtual memory
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When main memory fills up part of the hard disk is configures to act like the main memory (virtual memory). Although the parts of the program that are actually being executed need to be in the main memory, the volatile memory can store parts of the programs. The processor then swaps the different sections as it gets to the next part of the program, Access speed is much slower however so it doesn't always work well.
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discuss how changes in memory technologies are leading to innovative computer designs
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Capacity and density - Increasing the capacity on the same size card. Higher density means devices can store more without getting bigger. devices have become smaller and lighter and have bigger densities. Primary memory has also improved so more applications can be run at the same time.
Speed - Flash memory (slower than RAM) is faster than a magnetic hard disk so hard disks can be replaced with smaller, lighter, faster, more reliable flash memory. Price- Flash memory is cheaper and easier to produce so devices using it become cheaper also. |
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explain the need for secondary storage
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Secondary storage is the long term, non-volatile storage that holds the files and data that we want to store so it needs to be robust and reliable. It is usually much larger and cheaper than primary memory. Cheap memory technologies tend to have slower access speeds.
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describe common storage technologies such as optical, magnetic and solid state
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Magnetic
The oldest (used in floppy/ hard disks and tapes. Cheapest and high capacity. Slow access speed because tape drive has to read through the tape serially (tape) Limited lifetime (wears out with repeated used) Hard disks durable but vulnerable to movement when spinning but are very reliable. Very reliable if not damaged (affected by heat and magnetic fields. Good for backups and archiving, access speed to slow for general use. Optical Very cheap Small and portable Most computers can read CDs Faster access speed than magnetic tape Fragile (easy to scratch/ snap) Smaller capacity Quality degrades over time Slower to access than the hard disk. Solid state Doesn't have moving parts Access speed very high (not as fast as RAM) Good replacement for hard disk devices |
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describe flash memory
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Flash memory is significantly more expensive (per GB) than its optical and magnetic counterparts.
Direct access and relatively high capacity (2GB upwards) External device is slower than internal but is faster than magnetic tape and CDs/ DVDs. If used as internal storage it is faster that the hard disk. Very portable Very durable Limited Read-write cycles (limits useful life) Can be snapped when inserted into computer Very reliable |
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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
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For phones, personal use, notebooks, tablets and PCs flash memory should be used as it has a very high capacity, can be very light, very cheap, and has a fast access speed.
For Back up/ archiving CDs or DVDs should be used as they are cheap to produce, portable and have have a high capacity (CDs can also be used for software distribution). You could also use magnetic tape which has a higher capacity (up to 1TB) but it needs special equipment to use. |
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understand the need for input and output devices
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The role of an input device is to provide data for further processing. It consists of data/ commands entered into the computer system via an input device
The input data is then converted into digital data to be processed by the computer. An output converts digital data into some physical effect e.g print out of exam results from highest to lowest or a fire alarm. |
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describe suitable input devices for a wide range of computer controlled situations
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Keyboard
Pressing a key generates a character code Mouse A mouse detects movements and position to point at objects on the screen and select by clicking Touch screen Touch the icons to select, used on phones, PC, bank help screens and tourist info offices. Barcode scanner Laser scans the barcode to detect width of black and white stripes to generate the product number (rest of details found on database) OMR (optical mark recognition) Multiple choice/ evaluation forms/ lottery tickets Uses light source that reflects a different amount of light back from shaded boxes to detect input OCR (optical character recognition) Interprets marks as characters and generates text and some formatting detail into a word processing file. Sensors Measure temperature, light levers, pressure, other analogue events. These trigger processes and appropriate output action as required Microphone Input sound to be recorded in a file or processed by voice recognition software Joystick. |
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describe suitable output devices for a wide range of computer controlled situations
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CRT monitor
Cathode Ray tube. Old fashioned monitors. Heavy. glass screen more robust than TFT so used in factories. TFT monitor Thin Film Transistor. Variation of LCD (Liquid Crystal Display) technology. Take Less space but easily damaged. Speakers Output sound. Sound is synthesised from the digital file and outputs sound waves through speakers. Head phones (personal speakers) Inkjet printer Sprays ink onto the page. good quality at low cost. Never sealed on page so ink smudges. Quite slow. Laser printer Quicker and quieter. Ink is form of toner powder so is sealed onto page by heat rollers. Quality much better. more expensive and cartridges are too. Dot Matrix printer pre inkjet and laser printer. Like typewriter as printhead had to strike paper through an ink ribbon to print text on a page. Used where companies have to used multi part stationary. Pushes through several layers that have carbon paper on the back. Lights (LEDs) used to output lots of signals to USER |
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discuss input and output devices for users with specific needs
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Supermarket Point of Sale
Barcode scanner, scales, touch-screen, keypad, ship&pin reader, magnetic strip reader = LED display, Receipt printer, speaker, touch-screen Automated house for a disabled person Microphone, pressure sensor, movement sensor, digital camera, touch-screen = Lights, motors, monitor, speakers, touch-screen, switches Patient monitoring in a hospital Heart rate/ blood pressure/ breathing/ temperature sensor touch screen, buttons Specialised keyboards bigger keys, specialised layouts, braille overlays, brighter colour contrasts Foot operated mouse like normal mouse with left/ right buttons Sip-and-puff switches activated by breath. 'puff' = click, 'sip' ('suck')= holding key down. Used with on-screen keyboard Braille printer Impact printer creating raised dots to represent each letter to allow blind pepple to read |
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explain why data is represented in computer systems in binary form
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Because a computer only has two states, off or on, so everything stored in a computer can be stored as a series of 1s and 0s. (binary). Binary can be easily translated into boolean data and expressions as they deal with only either true or false. Boolean makes up a lot of programming expressions which is know as binary logic.
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understand and produce simple logic diagrams using the operations NOT, AND and OR
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NOT is a triangle with a little circle on the right point (output always opposite of input)
AND is a a kind of semi circle more like the letter D (only outputs 1 if both inputs are 1) OR is like an arrow or a kind of crescent moon (Out puts 1 if either inputs are 1 (but not if they are both 0)) |
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produce a truth table from a given logic diagram
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Q = X AND Y
X | Y | Q 0 | 0 | 0 For (X AND Y) to be true, X must be true 0 | 1 | 0 and Y must be true so all three of these 1 | 0 | 0 combinations are false 1 | 1 | 1 (X AND Y) is true because X is true and Y is true To combine gates you split them (kind of) Q = NOT (X AND Y) X | Y | X AND Y | Q 0 | 0 | 0 | 1 0 | 1 | 0 | 1 1 | 0 | 0 | 1 1 | 1 | 1 | 0 The first three columns we already worked out and above and then X AND Y and Q column is the NOT gate. Its easiest to work out each gate one by one, so do the first three columns first and then the next gate. |
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explain the need for the following functions of an operating system: user interface, memory
management, peripheral management, multi‐tasking and security |
User Interface is needed so that the user can communicate with the computer or computerised device.
Memory Management There is only a finite amount of main memory which gets used as programs and their data are stored which then set up locations and allocations of appropriate space based on the data types. The operating system must manage the space used by the programs and track everything at all times in order to increase efficiency and makes sure nothing gets overwritten. Once the program has finished it can then be removed from memory. Peripheral Management Manages peripherals by using buffers (queues) so that data isn't lost and allows other programs to use the processor whilst waiting for an input from the user. Multi-tasking/ Process Management Manages all programs so they all get enough processor time as well as managing priorities. Security Types of security depend on type of computer system. |
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describe the purpose and use of common utility programs for computer security (antivirus, spyware protection and firewalls),
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Antivirus
A virus is a program that is installed on a computer without your knowledge or permission with the purpose of doing harm. Prevents harmful programs being installed on the computer Prevents important files, like the operating system, being changed or deleted If a virus does manage to install itself, the software will detect it when it performs regular scans. Any virus detected will be removed. Firewall A computer connected to the internet is potentially accessible to anyone on the internet. Blocks access from the internet onto a PC or Network using factors like where the access is from (computer's address), type of traffic and specific web sites. Can also stop computers on a network from accessing specific sites or categories of site on the network. Spyware (programs that secretly record what you do) protection Runs in the background on a PC and detects and prevents spyware programs from installing, needs regular updates. |
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Describe the purpose and use of disk organisation (formatting, file transfer, and
defragmentation) |
Formatting
Hard disks in computers need to be formatted by the operating system to store files in the way the operating system expects. Most portable devices are already formatted. File Transfer & Management Provides a logical view of how the files are organised to make it easier for the user. Disk fragmenter Run to improve the efficiency of the computer by moving separate parts of the files around to be stored together (making the quicker to access). Also groups all free disk space together so all files can be stored in one place. It optimises disk performance. |
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Describe the purpose and use of system maintenance (system information and diagnosis, system
cleanup tools, automatic updating) |
System Information and diagnosis
Gives information about the hardware statistics about its use and information what will help diagnose any problems with the computer. System Cleanup tools Searches for and deletes files that are no longer needed (e.g. files used to install a software package). All temporary files can be deleted to clean-up the disk and improve performance. Corrects errors in settings and deletes unneeded ones. Regular use frees up disk space, speeds up how quickly the system boots and improves the performance. Automatic updating Makes sure that any software installed on the computer is up to date. Also checks the internet for updates and downloads and installs them if they are newer than the version already on the computer. |
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discuss the relative merits of open source and proprietary software
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Open Source
Software licensed for use but no charge for the lisence. Must be distributed with the source code (so can be modified by anyone) Developers can sell the created software Any new software must also be "open" so can be read and edited. Proprietary software Software that is sold as a license to use the software. Restrictions on how the software is used Those that wrote the software holds copyright (so users do not get the source code) Available help from the company Large user base with updates, technical support lines and training courses. |
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discuss the relative merits of custom written, off the shelf,
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Off-the-shelf software
Software bought in shops/ online. An application that someone has written and sold a license to use. You can use it straight away Cheaper than custom written software (as bought in large scale so don't have to pay development costs) Plenty of support available Regular updates and bug fixes from company Made to suit many people so there may be many features that you never use (software is unnecessarily complicated) Custom written software is written for customer to suit their specific requirements, not available to general public. Does exactly what you want it to do. No one else will have the software (making it more efficient than others maybe) Takes time to develop Much more expensive Unique so no wide range of available support No regular updates and bug fixes to download |
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describe a database as a persistent organised store of data
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A persistent collection of data or information which is held together in an organised or logical way. So it is a non-volatile wrote of data on a secondary storage medium e.g. hard disk.
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explain the use of data handling software to create, maintain and interrogate a database
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You can use off-the-shelf products like Microsoft Access to create Data handling software or you could create the database itself within the product and program a forms-based front-end application in a high level language. To create a database the data must be gathered and organised and then make a record for each product that stores all the relevant details about that product. The specific details will be stored as field.
The applications that use the data will interrogate (query) the database. Also a database must be maintained, meaning that when the data changes in the real world, the database must be updated to make sure the data stored is correct and up-to-date. |
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describe how a DBMS allows the separation of data from applications and why this is
desirable |
DBMS (Database Management system) is the software system that provides controlled access to the database (sometimes called program-data independence). This separation between programs and data is desirable as although sharing one database was better than having their own files (duplication leads to data inconsistency (some files were up-to-date but the rest of the company wasn't)), it lead to other problems being introduced e.g. security issues and issues with the applications being closely linked to the data. The applications were too closely tied to the database. This is why companies need DBMS
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describe the principal features of a DBMS and how they can be used to create customised
data handling applications |
Provides separation between the applications and the database
Allows multiple applications to use a single database Manage multiple applications trying to edit the same record at the same time (usually makes it read-only for second application) Provides appropriate views of the database to different users Provides security in terms of views and access rights Enables the creation of the relational database structure Allows applications to query/ interrogate the database Enables the creation of reports based on queries Allows the applications to edit and maintain the database (with appropriate access rights) Can provide automatic backups |
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understand the relationship between entities and tables
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Entities are objects or people that we store data about. In a relational database we create a table for each entity so a table is a collection of data about a specific entity. We use DBMS to create the tables and logical links between them (relationships)
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understand the components of a relational database, such as tables, forms, queries, reports and modules
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Tables - collection of data about a specific entity
Field- individual data items such as 'surname' or 'town' (column) Forms - to allow controlled access to the underlying database. There may be several different applications used the same data and each type of user will need different types of access. DBMS can offer different types of user different views. Queries - used to interrogate the database to find data matching specified criteria e.g. specific contact details or a list of people in a specific class. Reports- processed data from the tables or query results presented by DBMS as reports. Good reports should be dated, have a clear title, laid out clearly, have page number and in some cases it should be sorted into a particular order e.g. alphabetically, numerically, by product ID number. Modules - The storage of code written through a programming interface within the DBMS |
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understand the use of logical operators in framing database queries
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A query is used to interrogate the database to find data matching specified criteria. To write criteria there are a few rules.
Each part of the criteria is in brackets e.g. (County="Hampshire") AND (TutorGroup="SJR") This would retrieve students from the form SJR that live in Hampshire. There is also an order in precedence (like BIDMAS) for logical operators: AND takes precedence over OR so you may need extra brackets if the OR parts need resolving first. Not takes precedence over both AND and OR. e.g. (County="Kent") AND ((TutorGroup="11d") OR (TutorGroup="11b")) This would retrieve students from either of the tutor groups that live in Kent. |
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explain the use of key fields to connect tables and avoid data redundancy
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You can only create a relationship from one table to the primary key field of another.
Primary Key - The field that uniquely identifies each record in a table, it can be a number or text but must have a different value for this field. Foreign key - the other fields By creating a table for each entity rather than having all data on a flat file, you avoid storing the same data twice (avoids redundancy (duplication)) Benefits of reducing data redundancy: Reduces the risk of data inconsistency makes maintaining the database much easier Reduces the size of the database |
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describe methods of validating data as it is input
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Validation is used to check that the data being entered is reasonable and conforms to rules about the type of data allowed. There are several types of validation:
Range check (data is within sensible/allowed range) Type check (data is right type) Length check (not too long or too short) Existence check (checks product/ customer exists in the database) Presence check (checks data has been entered and not left blank) Format check (checks format is appropriate) Verification (data is entered twice and then the two versions are compared) Validation cannot tell if the data is correct, only if it is reasonable. |
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explain the advantages of networking stand‐alone computers into a local area network
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Sharing Resources:
Access files anywhere on the network and to different people Sharing peripheral devices and internet connection Communication: Email, messaging systems to chat whilst working, Transferring files between computers Centralised management: User profiles and security all managed centrally Software can be distributed across the network Users can see their own files on any PC on the network |
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describe, using diagrams or otherwise, the ring, bus and star network topologies
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Bus Network:
Computers are connected to a single backbone cable. All computers can transmit to each other but can only do this one at a time. This is fine if the network isn't busy but if there is a lot of traffic then the transmissions interfere with each other and computers have to retransmit. Ring Network: All computers are connected to adjacent computers in a ring, taking it in turns to transmit which is controlled by passing a token. The computer that has the token is allowed to transmit Star Network: All the computers are connected to the central computer via a cable of their own. The central computer controls the network and is usually a server where all the shared resources are stored. |
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describe the hardware needed to connect stand‐alone computers into a local area network,
including hub/switches, wireless access points |
Each computer needs a network card (Network Interface Card (NIC)) to connect to the LAN either by cable or wireless. Must be fitted for the kind of network connection required
In classrooms/offices, Computers tend to be star wired to a hub or switch despite looking like a bus network. The smaller star/ bus networks are then connected to a back bone which is either a star or bus topology. There's usually a mixture of topologies used. The central devices may be a server in a small star network but on a bigger LAN, the central device in a star will be a switch. |
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explain the different roles of computers in a client‐server and a peer‐to‐peer network
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Peer-to-peer network:
All computers have equal status Each computer is configured to share with other peer computers on the Lan which is more cost effective than having a specialised server/ person to run the network. Easy to set up and maintain No centralised management Backup each computer separately No dependency on a server Client-server Specialised roles: computers tend to be a client or server Needs a network manager to run the network Centralised security and management Back up done from central server Dependent on central server |
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describe the differences between a local area network and a wide area network such as the
internet |
A LAN is a collection of computers connected together within a single site.
A WAN is a collection of computers and networks over a geographically remote area. (connects separate sites and LANs together like the internet) |
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explain the terms IP addressing, MAC addressing, packet and protocols
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Each device on the internet must have an IP (internet protocol) address. Everything that makes the internet i.e. servers, computers, routers, all communicate using IP
Protocol is the set of rules that define how devices communicate covering how communication starts, transmission speed, significance of bits transmitted, how the bits are delivered, error checking procedures. MAC address is the unique reference number that is hard-coded into the NIC in order to transmit between devices within a LAN. It is a 48-bit address that is written as twelve hex digits. |
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describe the nature of the internet as a worldwide collection of computer networks
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The internet is a Wide Area Network that covers a worlwide collection of computers and networks all using IP to communicate.
The network is made up of routers (network devices) that form the backbone of the network, they also use internet protocol between routers. |
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explain the need for IP addressing of resources on the internet and how this can be facilitated by the role of DNS servers
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Each device needs an IP address to communicate of over the wide area. the IP address is made up of four (byte) numbers separated by three dots. The computers send the information as binary still.
As numerical addresses are hard for humans to remember, instead of remembering the websites IP address people enter the domain name (a text reference to the site). When the domain name is typed into the browser, the web page request is sent to a Domain Name System (DNS) server which has a database of domain names and IP addresses, so it translates the domain name into an IP address |
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describe the hardware needed to connect to the internet including modems, routers etc
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Modem:
Cheapest but slowest (only 56kb/s) Uses telephone network (analogue) to create from computer to internet (digital) Converts digital signal to analogue signal and vice versa at opposite end. Can only use the phone line for one transmission at a time. Local Router Connects all computer in the LAN to a wireless router for internet connection Uses fibre optic cable (delivers your cable TV service) or part of the phone line (connects house to local exchange) which uses broadband technology. Uses digital transmission all the way Allows use of computers/ phone line at same time offers speeds in excess of 2Mb/s |
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explain the importance of HTML and its derivatives as a standard for the creation of web
pages |
HTML is important as it is the programming language that all web pages are written in. It is used to describe the page content and coupled with a Cascading Style Sheet that defines how the content is styled.
In order for the web site to be access by other people it must be published to the internet either via your own web server or toe someone else's server (called 'hosting'). Internet Service Providers offer this as a service. |
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explain the need for security measures in networks, such as user access levels, suitable
passwords and encryption techniques |
safe from hazards such as viruses, hackers, hardware failures, software faults, natural disasters and other users.
Security measures include: Access rights User access rights: only access to what they need to. Read-only access when you can read files on a shared area but cannot edit them. Teachers will have Read-Write access. Data Protection Act stated employers must keep personal data secure so appropriate access rights is also a legal responsibility. Encryption A way of stopping unauthorised access to data such as intercepting anything transmitted over a network (as there are devices that can read network transmissions from the cables by scanning the emissions). Encryption changes the data before its transmitted and can only be deciphered with the appropriate key. Password Protection Easiest way to stop unauthorised access to computer or files is to use a combination of username and 'strong' password. Account can be locked after a number of failed attempts. |
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describe and justify network policies such as acceptable use, disaster recovery, failover,
backup, archiving |
Backup & Restore Procedures
Copy of all files which can be restored in the event of file corruption/ deletion. Usually made via removable hard disk or cassette tape (needs to be portable and high capacity) Archiving Stored data on magnetic tape that isn't used regularly but may be needed again or it is legally required that can be loaded onto the main memory. It frees up space on the main computer system Disaster Recovery Plan to continue work in catastrophic events that includes the ability to replicate the computer system in a very short time. Failover process of swapping to redundant component when hardware fails Acceptable Use policy A contract of acceptable use |
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explain the importance of compressing files that are transmitted via the internet
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When data is transmitted across the internet it will go via many different physical links between routers, the slowets part of the route being the connection from a computer/LAN to the internet.
Compression is a way of speeding up how quickly files can be transmitted across the network. Smaller files take less time to transmit. There are different types of compression though and the final use of the file will dictate how much you can compress so that the file is still usable. |
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describe the differences between lossy and lossless compression
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Lossy is where files are compressed by removing some of the detail (i.e. fewer colours mean fewer bits needed per pixel). Used to compress multimedia data e.e picture, audio files and video files. e.g.JPEG
Lossless compression is where the files are compressed but no data is lost (crucial for data text/ files). |
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describe common file standards associated with the internet such as JPG, GIF, PDF, MP3, MPEG
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JPG is a is a lossy compression and used by most digital cameras. Detail is lost but it is unlikely to be noticed.
GIF is likely to be noticed, also lossy, uses 8bits per pixel rather than 24. Solid blocks of colour can be seen rather than a transition. GIFs are fine for small pictures or thumbnails and take less time to load. PNG and BMP is a lossless version of the picture. MP3 is the dominant compression type for audio files as they can be downloaded very quickly and are very small in size. MPEG is the common format for video files. MPEG-1 is used for low resolution sequences, MPEG-2 is used for high resolution full screen video. PDF (portable Document Format) is an open file format, able to display a document on any hardware or any operating system. When created it captures all the elements of a printed page as an electronic image. PDF files aren't compressed but can be lossless compressed to reduce their size. |
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understand algorithms (written in pseudocode or flow diagram), explain what they do, and correct or complete them
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An algorithm is an outline of a solution for the problem that you attempting to sole through the program. Definition: a series of steps to solve a problem. Algorithms can be expressed in several ways e.g. system flow chart, pseudocode
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produce algorithms in pseudocode or flow diagrams to solve problems
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System Flow charts:
Symbols : Terminators (start/end, oval shaped) Input ( shows an input, parallelogram) Decision box (asks a question, has different routes out, IF process, Flat(ish) Diamond) Process (something happens (include a verb always) and rectangle shaped) Storage (file or database, shape is like terminators but has a semicircle removed from the right side so it kind of looks like one of those sock flag wind things idk.) Pseudocode Is an algorithm in programming-style constructs but not in actual programming language so the syntax doesn't have to be precise or detailed. It just has to be understandable and in a series of steps to solve the problem. It is also indented like a real program and is good to use PascalCase format (no spaces, words capitalised) to name items. |
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understand and use sequence in an algorithm
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Sequence is the first of three pseudocode constructs and it is just writing the steps down in the order they need to happen
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understand and use selection in an algorithm (IF and CASE statements)
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There are two basic selection constructs:
IF.. THEN.. ELSE allows you to choose between two options. If you nest these or have several in a row you can choose between several options but the CASE statement achieves this more efficiently. IF.. THEN there are two methods, one where they are all separate which isn't very efficient but does work and the other where the multiple IF statements are nested so that the computer will only execute the IF statement tests until it finds one that is true. Its relatively hard for a programmer to follow though. The CASE statement is designed for coding multiple choices in a program where the user will enter one choice for example. It is much clearer than the IF statements. |
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understand and use iteration in an algorithm (FOR, WHILE and REPEAT loops)
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There are three basic iteration (loop) constructs. Conditions (which are boolean expressions) are used to control iteration and selection statements.
The FOR loop allows you to execute a group of steps 1 or mote times, for a specific number of times. The REPEAT loop is controlled by a condition at the end of the loop and therefore will always execute the following steps at least once. The WHILE loop is controlled by a condition at the start of the loop and will therefore execute the following steps zero or more times. An example of this would be when reading a file when you need to check if the file is empty before you read from it. |
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explain the difference between high level code and machine code
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Machine code is
Processor specific (one lang per processor) Designed with hardware in mind One assembly lang command (which is processor level code, written in mnemonics) translates to one binary instruction in machine code Translated using an assembler High level code is Portable (works across different machine and processors Designed with a type of problem in mind One high level program instruction translates to several machine code instructions Translated using a compiler/ interpreter |
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explain the need for translators to convert high level code to machine code
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It needs to be translated into machine code so it can run on the processor. Translators are a type of system software
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describe the characteristics of an assembler, a compiler and an interpreter
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Assemblers:
Converts assembly language into machine code Simple conversion as every assembly lang instruction is translated into a single machine code instruction Compiler Translates the whole program to produce the executable object code The object code is the version that is run Faster run time as the program is translated once (object code run after that) Customers can't see actual program written after distribution Used for distribution software Interpreters Translates and executes one line at a time Source code is the version run Slower run time as program is translated every time its run If distributed source code with interpreter then actual code would be able to be seen Used in development Both Compilers and interpreters convert high level programming lang into machine code. More complex conversion as a single instruction translates to many machine code instructions. |
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define the terms variable and constant as used in an imperative language
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A constant is a value that remains the same while the program runs. We declare constants at the start of the program so when its value changes, you only have to edit it one place and by having an identifier for the value the code will be easier to read and understand, making it easier to debug and maintain later on.
A variable is an identifier associated with a particular memory location. The value may change as the program is run and new values are assigned to it. A variable also has a data type that defines the type of data that'll be stored (and therefore operations that can be performed) and how much space that will be needed for that data item. |
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describe the data types integer, real, Boolean, character and string
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Integer
is a whole number e.g. 3, 46, -98 (typically 2 bytes of memory) Real is a number with a fractional part e.g. 3.45, -9.32 (typically 4 bytes) Boolean is a variable that have the value True or False (typically 1 byte) Character (Char) is a single character, this can be any letter, digit, punctuation mar or symbol that can be typed (typically 1 byte) String Zero or more characters. (could be empty), one character or several. Most languages have a limit of 255 if the programmer does not specify the maximum size. |
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select and justify appropriate data types for a given program
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On numerical data types arithmetic (e.g. +,-,*,/,DIV (interger division), MOD (modulus) and comparison (e.g. <,>,<=,>=,<>,=) operations can be performed.
When performing operations you must consider the data types e.g. in a simple calculation of two whole numbers added together you can define both variables as integers. But if the calculation involves division then the variable that stores the answer must be declared as a real number. DIV and MOD can only be performed on whole numbers, integers. DIV is like normal devision but returns the whole number of times one number goes into the other. MOD gives the remainder of integer division. |
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perform common operations on numeric and Boolean data
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Data type - Operations that can be performed:
Integer - Arithmetic/ comparison operations Real - Arithmetic (bar DIV and MOD) / Comparison operations Boolean - logical operations |
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Use one‐dimensional arrays
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We use an array to make processing groups of data easier to code. An array is a group of data items of the same data type that is stored under one identifier in contiguous (one after another) memory locations.
Benefits of using arrays are that the code is easier to follow and a group of data can be easily processed using a FOR Loop. Individual boxes in the array can be used just like variables: Assign values to them: Numbers[4]=27; Read values into them from keyboard/ file: Read(numbers[4]); Write values stored in a box to the screen or a file: Write('The fourth value is ',numbers[4]); |
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describe syntax errors and logic errors which may occur while developing a program
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Syntax error is an error in the format of the program statements e.g missing semi colons, keywords spelt incorrectly, missing brackets, having an incorrect number of parameters inside brackets for functions
Logic error is an error in the algorithm that means the outcome is not as expected, even though the program will run e.g. missing brackets around calculations, loops not executing correct number of times because of incorrect condition, variables not initialised/ in the wrong place, flawed algorithms. |
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understand and identify syntax and logic errors
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A program will not compile and run if there are syntax errors, luckily there are some good debugging tools that can detect syntax errors.
Logic errors are hard to spot, you need to do some systematic testing to make sure the program really does behave as expected. |
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select and justify test data for a program, stating the expected outcome of each test
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You need to decide on some sensible test values to put into the program to test that the outputs look as expected. To make a test plan use this structure:
Test purpose | Test data | Expected outcome | Actual outcome. First three columns are planning and fourth is completed. You need to test the boundary data (testing the both ends of the allowed range of data, data not allowed and just outside the range) |
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describe common tools and facilities available in an integrated development environment (IDE): editors, error diagnostics, run-time environment, translators, auto‐documentation
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Editors
Decent text editor, could provide other features such as indenting, colour and auto-formatting Error diagnostics Run-time environment The code is run within the IDE as if it were a CPU, this saves a lot of time during the development. Translators Either compile or interpret the code, the compiler will check the syntax and report any errors, then it can convert the high-level code to machine code. Auto-documentation IDE takes a note of all variables, modules, sub-routines, comments and the developers comments to generate a text file that can be the basis of the programmer's technical documentation. |
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Advantages and disadvantages of using the Bus Network
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Advantages:
Less cabling is used than the star network It's easy and inexpensive to install Easy to add another computer Disadvantages: If the main backbone cable fails then the whole network goes down Cable failures are hard to locate as it affects all of the computers Performance slows with traffic increase |
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Advantages and disadvantages of using the Ring Network
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Advantages:
Not dependent on a central computer (like the star network) The token passing network is simple and therefore reliable Consistent performance even with high traffic Disadvantages: A single node or link failure and the network is disrupted |
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Advantages and Disadvantages of using a Star network
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Advantages:
If one cable fails it only affects that station rather than the whole network Consistent performance even if if the network is heavily used Easy to add computers More secure as messages go straight to the centre Disadvantages: Can be costly due to amount of cable used Dependent on the central computer |
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What are the advantages of using DNS servers
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Humans don't have to remember/ type numerical addresses
If the IP addressses change the users can continue to use the Domain name as the DNS servers update their databases regularly (if the local DNS server doesn't have the domain name listed, the page request can be forwarded to another DNS)/ There are many DNS servers to everyone has access to all addresses from their local DNS server |
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In Network security measures, what are Preventative measures for?
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Aimed at stopping a hazardous event from occurring. E.g.:
Access rights Firewalls Physical security (locking rooms) Passwords Encryption Acceptable use policy |
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In Network security measures, what are Detective measures for?
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Aimed at detecting when data has been corrupted or systems have been compromised
e.g. Virus checking software Firewall software Fire alarms Audit trails |
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In Network security measures, what are Crrective measures for?
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Aimed at correcting or restoring the system after problems have occurred.
E.g. Backup and Restore procedures Redundant hardware / Failover Disaster recovery procedures |
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What is Failover?
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The process of swapping to the spare/ redundant component when the hardware fails, this process happens automatically and transparently (user doesn't notice). A system with lots of redundancy built in is described as fault-tolerant as when the system faults it can cope with it.
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What is Backup and Restore Procedures?
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A network will backup servers regularly so that in the event of files getting corrupted or deleted a copy of all the user's files can be restored. Normally made via a removal hard disk/ cassette tape. The medium must be high capacity and portable so can be stored in a fire-proof safe/ off site.
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What is archiving?
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Large amounts of data that is legally required to kept or might be needed again but is not needed on a regular basis is taken off the main system and stored, usually on magnetic tape (as it's cheap), and can be loaded back onto the system if it is needed again.
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What is Disaster recovery?
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For companies that wouldn't be able to operate if their computer systems went down. Able to replicate the computer system temporarily e.g. regular backing up of data, duplicate hardware system being available, back up data restored on new hardware. Could buy own redundant hardware, more likely to pay a disaster recovery company for their service.
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What is Acceptable Use Policy?
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A contract between you and the school/ company stating that you agree to only use the network for certain things. You can be sacked if you go against this agreement.
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Why does an operating system need a user interface?
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A WIMP interface (windows, icons, menus, pointers). Operating systems have to provide appropriate ways for the user to interact. Interfaces vary with the device e.g. touch screen, buttons that perform specific functions and controls for central heating or within cars all computer systems need to be interactive.
Some have a command-line interface that is just a text prompt where the user types a command. |
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Why does an operating system need to manage memory?
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The main memory has a finite size so the operating system must manage where in memory the programs will go. When programs start they get copied from the disk into main memory and the processor is given the address of where it starts. Programs and the data are stored in the same main memory. When the programs starts it will set up locations in the memory allocating appropriate space, based on data types. The operating system must manage space used by the programs and also track where programs and data are at all times to make efficient use of the space in memory to make sure nothing gets overwritten by anything else. When a program is finished it can be removed from memory and new ones will be loaded into memory.
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Why does an operating system need to manage peripherals?
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The operating system must manage all peripheral devices (including the hard disk). Writing to storage/ output device is slower than moving data around in the CPU it uses buffers (queues) to make sure data isn't lost. Reading from storage/ input devices is also slow so the operating system allow other programs to use the processor when it is waiting for an input from a user.
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Why does an operating system need to multi-task/ manage processes?
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A modern processor runs many programs at once but (presuming its a single core processor) is can only execute one instruction at a time. The processes take it in turns to use the processor to execute instructions. The operating system needs to manage all the programs so that they all get enough processor time. It also has to manage priorities as well. While one program is being executed by the processor, other programs wait in main memory
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Why does an operating system need to manage security?
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Types of security depend on type of computer system. e.e. PC security offers different types and levels whereas a washing machine needs to make sure that the user isn't allowed to open the door whilst its full of water. May include additional features to make it easier to maintain and use e.g. virus checking software, firewall and parental controls.
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