Condensed revision guide for OCR GCSE IT- everything you'll need for paper 1 and 2, as well as programming skills, are fully covered in an easy-to-read and clear format with colour coding throughout!
Computer Systems
Integrated System of hardware and software that enables data to be input, then processed and the results
communicated to the user.
Input Computer systems:
Information converted to data Less space
Validated [check to make sure it’s the right type] Searches
Verified [accurate] More than one person
Process No loss
Turning data into something else Fewer staff for maintenance, no clerks
Central Processing Unit Reports generated quickly, not time
Output consuming or human errors
Communication Expense of setting up
Screen display or printed paper Training costs for technicians
Data converted back into information System failures or power cuts – data loss or
Information can be used to feedback more input corruption
data Security – unauthorised users or hackers
Types of a Computer
Mainframes
Banks, search engines e-commerce
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
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
,Configurations
Star each connected to central computer [mainframe or server]
Performance unaffected by other workstations Network Security
Cable failure less of a problem Physical Serial numbers
Central computer or server failure Alarms
Most cabling – expensive Fire protection
Bus/Line line of cable sends data, where terminals are connected Locks
Cheapest – least cabling Avoiding ground floors
Slow, as all data on central line Blinds on windows
Central cable failure
Ring one direction of flow, in a ring Access User names + passwords
Cheap to expand Changed frequently
Fast – only one direction of flow Access right
Slower if many users Firewalls
Ring cable failure Transaction logs
Data Password protected files
Read only/hidden
Compression for Backups
Archiving
Parts of a computer
OPERATING SYSTEMS
The software that enables applications and the rest of the computer system to work, e.g. Windows Vista, Mac OS X
1. Enable applications software to communicate with the hardware.
For example, clicking on a web address, so the OS knows it wants Internet access
2. File input and output, and peripherals
3. Common tasks for applications
4. Operate utilities, such as print managers and virus-scanning software
5. Allocate system resources as requested by applications
One program at a time – allocate entire system’s resources to the current application
Multi-tasking – many programs at once; share out resources such as CPU time and memory;
communication with peripherals, such as internet, also need to be shared
Multi-user – many people log into a computer and use it at once; can be WAN so miles apart;
sharing tasks, as well as workstation tracking.
Security Programs cannot inspect one another’s resources
Only resources for which they have permission can be accessed.
User interfaces
Command-driven
Blank screen, user types commands which OS carries out.
Once user learns commands, system is quickest to use
Takes very long to learn commands
Different software will have different commands
Menu--driven
List of commands or options under headings or menus – clicking
No need to learn commands
Slow
Cumbersome
Logic behind structure may not be clear to user
Graphical User Interface [GUI]
Popular; menu-driven with icons to represent main commands
WIMPS Windows [information relevant to one particular task]
Icons [picture representations]
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. Dictation instead of typing is good, but a lot of memory space
Scanners
Pictures to digital data
Colour and brightness dependant code, which computer builds up a map of
Bitmap files are large – memory
Optical Character Recognition
Familiar patterns for text and numbers
Proof reading
Magnetic Ink Character Recognition
Banks for cheques
Iron containing ink – when magnetised scanner reads numbers
Accurate but expensive
Optical Mark Recognition
Registers/Exams – carbon reading scanner
Quick and accurate, if OMR sheet filled in properly
Magnetic Chips and Stripes
Chip and pin cards – pin must be check with pin on chip for information
Magnetic Tape on back of bank cards
Digital Cameras
Pixels – photo editing software can be used; no film needed, immediate, much memory as high resol.
Laser Scanners
Supermarkets and Libraries; bar code with product’s data
Faster and less human error; expensive and computer system must b accurate to work
Graphic Pads
Joystick
Touch screens
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