IT NOTES FOR AQA SPEC B

I made these notes from the CGP AQA ICT book.

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  • Created on: 10-05-11 18:38
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Computer Systems
Integrated System of hardware and software that enables data to be input, then processed and the
results communicated to the user.
Input
Information converted to data
Validated [check to make sure it's the right type]
Verified [accurate]
Process
Turning data into something else
Central Processing Unit
Output
Communication
Screen display or printed paper
Data converted back into information
Information can be used to feedback more input data
Computer systems:
Less space
Searches
More than one person
No loss
Fewer staff for maintenance, no clerks
Reports generated quickly, not time consuming or human errors
Expense of setting up
Training costs for technicians
System failures or power cuts ­ data loss or corruption
Security ­ unauthorised users or hackers
Types of a Computer
Mainframes
Banks, search engines ecommerce
A lot of processing
Reliability
Multiple copies of parts ­ failure of one is insignificant
Servers
PCs without inputs, e.g. keyboard
Connect servers and set like single machine
Easy to increase or decrease amount of processing power by adding or removing individual servers
Enough servers together, make a system as fast as a mainframe for less money by not good at large
amounts of data because data must be shared.
Also, hardware failure common
Microcomputers
Used microprocessors ­ slower at first, became faster
PCs ­ small computer for personal tasks ­ more powerful so mainframes are cheaper than before
Networks ­ connection, communication
Local Area Network
Network File Server dedicated computer that runs software and stores files created
Workstations individuals software and files can be made
Print server for a shared printer ­ queues printing
Wire/O.F/Radio data sending to and from
LANS don't need a server ­ could just be a few computers connected for files and software
Wide Area Network
Server operates the network

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Microwave links or satellite channels or telephone lines
Peripherals such as printers and software can be shared
Remote location based oil engineers can work
Storing files centrally makes less vulnerable to workstation failure
Communication ­ cheap and fast
Expense of cabling ­ install and replace
Fault with server crashes whole network
Security measures to restrict access and viruses…read more

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Configurations
Star each connected to central computer [mainframe or server]
Performance unaffected by other workstations
Cable failure less of a problem
Central computer or server failure
Most cabling ­ expensive
Bus/Line line of cable sends data, where terminals are connected
Cheapest ­ least cabling
Slow, as all data on central line
Central cable failure
Ring one direction of flow, in a ring
Cheap to expand
Fast ­ only one direction of flow
Slower if many users
Ring cable failure
Parts of a computer
OPERATING SYSTEMS…read more

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Menus [list of options]
Pointers [arrow to move screen]
Input
QWERTY keyboard
Key connected to a switch, sending a signal to CPU
Typing skill needed or can be slow
Concept keyboard
Shops/restaurants with options representing data
Mice
Clicking gives a command, held down for dragging
Direction and speed ­ pointing
Optical watches surface below's movement Old have balls that rotate and move sensors
Microphones
Voice recognition systems convert sound into text or commands for a computer, or digitally record
sound.…read more

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Touch screens…read more

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The CPU
Runs computer programmes, responding to user input
Generalpurpose
Instructions
Program is a list of instructions for CPU, which it performs in order
Load/Store Instructions ­ moving a piece of data move data from memory to CPU and back
Arithmetic Instructions ­ operations and functions
Control Signals ­ temporary more important things, other work resumed after
Output
Printers
Dot Matrix
Printhead is matrix of pins ­ characters formed by using a set pattern of pins
Ribbon ­ long strip of material with ink on…read more

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Computer Memory
Random Access Memory
Read from to written to
Volatile RAM keeps contents when power is on
Nonvolatile needs power to change contents, but contents are stored
Programs for the computer is on the RAM [easy access]
Read Only Memory
Data and programs for CPU are put onto ROM by manufacturer ­ no new data can be added
ROM is permanent memory ­ instructions that enable the OS to be loaded into the RAM
Small amount of ROM compared RAM
Nonvolatile
Backing Storage is…read more

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Using the system
D A T A
Data needs to be gathered first ­ this is data capture i.e. the input
Obtain the information ­ record and convert into a form suitable for use with the computer system
Enter the data into the computer using an input device
Datacapture forms/Questionnaire Paper based
Need a human operator to key in the results by hand
Some datacapture forms need operator to enter information by code [e.g. OMR]
Necessary ­ e.g.…read more

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Fixedlength fields ­ some waste space but computers can manipulate quickly
Variable length ­ less memory, but longer processing time…read more

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P R O C E S S I N G T H E D A T A
Real Time Processing
Processing as soon as entered, within a time window
Quickly respond to changing information
[Air traffic control/Safety devices/Inflight navigation/Quality monitors]
Necessary, but can be expensive as processor is always ontask
Batch Processing
Different jobs stored up and processed together at once
Large databases where there can be a delay
[Wages are done every month]
Large volume of data processed at regular intervals
Transaction Processing
Division…read more

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