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| The physical components that make up the computer. |
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| The programs and applications on a computer. |
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| Used in businesses. Often has many terminals, such as EPOS machines, attatched to a central minicomputer. |
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| Used by large oragisations eg. Banks, insurance companies. May have thousands of terminals in far away locations. |
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| Can cost millions of pounds. Mostly used for scietific research, weather forcasting and in very large organisations. |
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| Fetches, decodes and executes instructions |
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| Holds RAM/ROM. Is divided into bytes |
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| Random Access Memory. Holds the program currently running. Is volatile and is lost when the machine is turned off. |
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| Read Only Memory. Non-volatile. Holds the boot-strap loader. (boot-strap loader instructs it to load the OS into main memory”booting up/reboot”) |
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| Stores recently and frequently used instructions. |
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| Also called auxillary storage, external memory. Stores information and programs that you may not be using but might need later. |
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| Input devices give information to the computer. Output devices printers, speakers etc. |
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| Performs tasks needed to run the computer. |
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| A set of programs that allow the user to perform tasks. Makes the link between programs and hardware. Is needed to run programs on a computer. Eg. Linux, Mac OS X, Windows |
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| Non-essential programs that perform one task that helps the computer run more efficiently. Eg. Virus Scanners, Compression software |
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| Programming language compilers, interpreters and assemblers |
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| Compilers & Interpreters translate high level language (VB, Pascal) into machine code. Assemblers translate assembly code (low level language) into machine code. |
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| Designed to carry out task independent of the computer. Eg. Letter writing, drawing. |
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| General Purpose Applications Software |
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| Software that can be made to do many different tasks. Eg. Microsoft Word, Photoshop |
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| Software designed to do a specific task. |
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| Software designed specifically for a person or corporation. |
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| Advantages of Off-the-shelf |
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Definition
Less-expensive
Can speak to other users of the package
No waiting time for it to be programmed
Fewer bugs than newer software
Well documented
Training may be available |
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Designed to do exactly as the user wants
No unwanted features
Can be written to run on specific hardware
There may not be a suitable software package on the market |
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| A binary digit (1 or 0) is a bit. 8 bits together is a byte. One byte holds one character. |
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| True or False, 1 or 0, + or - |
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| A different code for each character eg. U = 1010101 |
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| International 16bit coding scheme. |
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| Binary Coded Decimal. Each decinal is represented by a 4bit code. Eg. 1 = 0001, 2 = 0010, 3 = 0011. No rounding occurs. Takes up more bits. When the sum of two binary numbers is greater than 9, 6 must be added. |
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128 64 32 16 8 4 2 1
1 0 1 0 0 1 1 0
128 + 32 + 4 + 2 = 166 |
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| The main memory can be thought of as a series of boxes, each on containing a byte. The number of boxes is measures in kilobytes, megabytes a gigabytes. |
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| The number of bits and Processor/CPU and process symultaneously. Word Size in measured in 8-, 16-, 32- or 64- bit word sizes. |
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| Data collected for a specific purpose. Eg. Times and employee clocks in and out. |
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| Data originally collected for a different purpose. Eg. Credit card companies selling lists of well travelled customers to Travel Companies. |
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| An Analogue to Digital converter converts anologue input to digital form ie. a binary pattern, so it can be stored and processed. Anologue sound may be represented by wave forms, and the height of the waves can be sampled and then represented by a 16bit code. The more samples are taken, the better the quality. |
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| Image is made up of pixels. 1 byte of memory = 256 colours, 2 bytes = 64, 000 different colours. |
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| Instead of pixel by pixel, the thickness of the lines and their start and end points are saved. Shapes are represented by mathmatical formulae. |
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| Machine Code - First Generation |
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| Executes directly without translation. Only 1s and 0s. |
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| Assembly Code - Second Generation |
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| Uses mnemonics and denary numbers. Needs an assembler to translate into machine code. Uses up little space and executes quickly. Machine dependant, each type of computer has it’s own assembly code. |
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| Imperitive High Level Languages - Third Generation |
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| Eg. Basic, Pascal, Cobol. Not machine dependant. One statement is several machine code instructions. |
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Code written by the programmer
The compiled Code |
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| Translates Assembly code into machine code. Assembler is machine dependant. |
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Definition
Translates high level language into machine code. Compiler translates the entire code so it can be run without a compiler next time.
–If error is found in program the whole program needs to be recompiled.
+Executes faster.
+More secure, cannot be read without a good deal of ‘reverse enjineering’. |
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Definition
Also translates high level source code, but translates one line at a time and then executes it. No object code is produced, program has to be re-translated every time it is run.
+Useful for program development, not need for lengthy recompilation.
+Useful for debugging and to partially test the program. |
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Term
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Definition
| FIFO. New elements go on the end of the queue, data can only be retrieved from the front. Pointers mark the front and rear. Eg. Output waiting to be printed, characters typed onto a computer are held in a queue in the keyboard buffer. |
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| LIFO. Only accesed at one end. Items are added (pushed), or removed (popped). Pointer marks the top. |
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| Overflow and Underflow (Queues and Stacks) |
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| Adding a new item when the queue/stack is full, removing and iten when the queue/stack is empty. |
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| A bus is a series of parallel wires connecting components of the computer. When the CPU needs to access a main memory location, the address is sent on the address bus. The data from the location is sent on the data bus. Control signals are sent on the control bus. |
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| Bits are sent one bit at a time over a single wire. |
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| Parallel Data Transmission |
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Definition
| Several bits are sent symultaneously over a number of parallel wires. Used inside the computer and over distances of a few metres eg. To a printer. Faster, but becomes unsynchronised over long distances. |
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| The speed at which bits are serially transmitted. |
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| The rate a signal changes. |
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| The range of frequencies that a medium can correctly transmit. |
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| Computers use odd or even parity. If the parity is even, the number of ‘on’ bits must be even. The parity bit is set at the transmitting end, and checked at the receiving end. |
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| Asynchronous Data Transmission |
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Definition
| One character at a time is sent, which each preceded by a start bit and followed by a parity bit and a stop bit. |
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| The exchange of signals between devices to make sure they are ready to send and receive data. |
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| Rules for communication between devices. |
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| Local Area Network. A method of connecting computers together in one building or site. |
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| Converts data from a computer into a form that can be transmitted over the network, and converts data received from the network into a form that can be saved onto the computer. |
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| Sharing of resources like printers, scannerd and modems. Easier to share information held on disk drives and back up information on one file server. Easier to store applications on one computer than having to install them on all the machines individually. |
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| Disadvantages of Networks |
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Definition
| If one network file server breaks then many users cannot run applications. A badly managed network may operate less efficiently than stand alone machines. As traffic increases the network performance degrades. Difficult to keep secure from hackers. |
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| Star Network: All computers connected to a central host computer. Each node is independent so if one fails the others are not affected. However, if the central node fails then all of the branches fail. Costs a lot of cable but easy to add extra branches. |
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| Bus Network: All computers share a single cable, lowers cost. Whole network goes down is main cable fails. Network degrades under heavy load. Many users at once may result in system grinding to a halt. |
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| Ring Network: Data only goes in one direction. No dependance of central computer. If one node breaks down, whole ring is disrupted. |
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| Connects graphically remote computers in different sites, cities or continents. |
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| Public Telephone Lines, Radio waves, Communications Satellite. |
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| Convert digital information into analogue so it can be transmitted over phonelines. Also converts the analogue signals back into digital. |
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| Factors Affecting Data Transmission |
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| The speed of the modem. The type of cable used. Whether synchronous or asynchronous transmission is used. |
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| Using a telephones network to connect to a network. |
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| A dedicated line connecting geographically remote computer systems is permenantly on. |
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| Uniforn Resource Locator. |
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| Binary Digits. Either ‘on’ or ‘off’ / 1 or 0 |
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| 8 bits. Can represent one character/one pixel. |
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| Characters are grouped together to form fields eg. ID number, Surname, Postcode |
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| All the information about a person or item is held in a record. |
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| A collection of records. Eg. A Payrol file containing the records of the employees. |
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| A collection of many files. |
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| A unique identifyer in a record eg. ID Number |
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| SecondYay (Alternate) Key |
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Definition
| Not unique but used to find a group of records. |
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Definition
| The start and end of the records and the different fields are seperated with * or hash symbols. This means they take up less space. Harder to update records. Harder to estimate file size, as oppose to fixed length records with a set number of bits set aside for records. |
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| Contains details of all transactions that occurred in a set period of time. |
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| A permenant file of data. |
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| Contains data used by the program during processing. |
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| A collection of records stored one after the other in no particular order. Records cannot be deleted, this would leave a blank space, so a new tape must be made. |
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| Sequential File Organisation |
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| A collection of records stored in the order they were keyed in. Same as serieal, deleting or adding records requires a new tape. |
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