CG3 computing Wjec

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  • Created by: Tom
  • Created on: 12-01-13 12:39

File Organisation

Indexed sequential file - were records are stored in key sequence order and where an index is used to allow data to be accessed directly

Multilevel index - when the main index contains a range of addresses and the location of the next level index. several levels may occure with the last index containing the physical address of the record


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File backups

Generations of files - a generation file backups system involves storage of serveral of the most recent versions of the master file. files can be called son fathers and grandfather refering to the age of the file

useful if one version is corrupted the previous versions are still availible to use

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Half Duplex, Full Duplex and Simplex

simplex - data can be transmitted only one way, one at a time

e.g radio

half duplex - data can be transmitted in both directions, one at a time

e.g Walkie Talkie

full duplex - data can be transmitted in both directions at the same time

e.g Phone

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Packet Switching

Packet Switching - is were data is split into packets beforre transmission. each packet maybe transported by different routes through the network. they may arrive out of order and are then re-assembled on arrival. in addition to the actual data the packet will contain the order the packet needs to be reassembled source and destination.


  • high level of securtiy becasue of the ramdom paths that may be taken by each packet in a set
  • less likely to be effected by network trouble
  • no waiting during gaps
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Data Collision

Data Collision - data collison occurs when two pieces of data interact on the network casuing data corruption. a network deals with collisions by each sender waiting a random time before resending the data

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Multiplexing - when several independent data sources are combined to be snt along a single route to a single destination

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Queues and Stacks

Queue - is first in first out (FIFO) data structure

it is the most apporiate in printer queues , keyboard buffers, download buffers and processor schedulling queue

Stack - is First in last out (FILO) data structure

it is most apporiate in subprogram return address, recursion values, short term arithmetical results, revesing a queue or list and an undo funciton

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Network Protocol

Network Protocol - necessary tp enable computers/devices to communicate with each other

e.g linking a printer to a computer and linking mobile phones via bluetooth 

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Parallel Transmission and Processing

Parallel Transmission - occurs when a number of bits are sent simultaneously

useful for increaing the speed of transmission

Parallel Processing - the simultaneous use of several processors/cores to perform a single task

useful when an extremely large calculation needs to be procesed 

e.g image processing 

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GUI (graphical user interface) 

  • easier for a novice user to learn
  • more intutive to uise once learned (icons relevant to the application)
  • may be similar to other packegs
  • no need to remember long text comands 
  • users can customize desk-top e.g shortcuts
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Voice Print Recognition

Voice Print Recognition - the process of capturin gthe person's voiceprints then digitising and storing the is data pn a computer system. when the entry is attempted, the voiceprint of the person is captured. two data items are compared, with entry being allwoed if there is a match

  • persons voice originally cpatured, digitised and stored
  • on attempted entry, person's voiceprint cpatured (and digitised)
  • digitsed data compared( and entry allowed if sucessful
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Xor gate and encription


Data  10111101

key    10001100

en D   00110001 

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Quick Sort

Quick sort - is and example of a recursve Algorithm which is an algortihm which calls itself until a terminating condition is met

  • an item/pivot selelcted 
  • produce two new lists of smaller and larger number
  • repeat above points on new sub lists until sorted
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