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Computer science unit 1 (1.4 (1.4.1 (Wide area networks (uses public…

- - - - SRAM
        
        FAST
        
        EXPENSIVE
      - DRAM
        
        SLOWER
        
        CHEAPER
- - - - Has its own infrastructure
        
        routers
        
        switches
        
        cables
      - Typically found in homes/schools
    - - uses public infrastructure to lower costs
      - connects two or more separate lans together
      - can create thier own connection but it is expensive
      - found in large businesses
    - - share data/files/ information
      - share peripherals
      - admins
      - login from any computer
    - - client server
        
        relies on a central server
        
        client request services from the server (printing)
        
        files are stored centrally
        
        suited for large amounts of computers
      - peer - to - peer
        
        all computers on the network have equal status
        
        each computer acts as a client and a server
        
        files are stored on individual machines
        
        back up must be done one an individual machine basis
        
        suited for a low number of computers
    - - Provides encrypted 'tunnel' between machines
      - Allows for secure transfer of data
      - software based private network
  - - - ip address of the sender
      - ip address of the receiver
      - Its position in the sequence
      - Timeout time
      - Verification that it has arrived without corruption
  - - - Allows wireless devices to connect to a wired network
      - advantages
        
        quick installation
        
        no building work required
        
        visitors can access easily
      - disadvantages
        
        slower and less secure
    - - handles the packets
    - - Used to join segments of a network togther
      - connects two or more devices together to stop data collision
    - - alllows a computer to connect to a wired network
      - provides a unique mac address for each client
    - - ethernet (slower)
      - fibre optic (fast)
  - - - how fast data can be sent
      - measured in bits per second
    - - too many can slow the network
    - - wired vs wireless
      - fibre optic vs copper
    - - poor connection increases errors
    - - A delay between sending and receiving data
  - - - increase storage
      - access anywhere
      - collaborate with others
- - - - some or all devices are connected directly to each other
      - Most are usually connected to a node
    - - Each devices is connected by an individual cable directly to the server
      - Usually used in schools and offices
    - - Stable connection
      - Reduced possibility of hacking
      - More secure
      - Faster transfer speed
      - Good quality of signal
      - expensive cost of wire
    - - Cheap set up
      - User have more freedom
      - lower transfer speeds
      - More vulnerable to hacking
      - Interference can occur
    - - Scrambles the data so it cant be read
      - A key is needed to decode it
  - - - A unique address for the device
      - Its embedded in the hardware and cant be changed
      - Its made up of 48 bits (6 bytes) written as hex
    - - Each device on the network has a unique IP address
      - The address is written in denary
      - The first number indicates the class of network the user is on
    - - Hyper text transfer protocol
      - Hyper text transfer protocol secure
      - File transfer protocol
      - Post office protocol
      - Internet message access protocol
      - Simple mail transfer protocol
  - - - Contains all the application that may with to exchange data of files
    - - Creating and sequencing packets on a WAN
      - Divides the data into packets and sends them to the internet layer
    - - Routing the packets on a wan
    - - Creating and routing frames on a lan. Error checking
    - - Methods of encoding bits onto wired and wireless frequencies and channels
- - - - main memory
        
        RAM
        
        holds data and instructions
        
        located on motherboard
        
        volatile
        
        ROM
        
        non volatile
        
        read only
        
        bootstrap loader held here
      - i/o controllers
        
        Used as an interface between a hardware devices external to the motherboard (keyboard mouse)
      - buses
        
        A set of wires connecting two or more components of the system
        
        address bus
        
        carries addresses from the processor to main memory
        
        one directional
        
        data bus
        
        carries data from main memory to the processor
        
        works both ways
        
        data can be read/writren
        
        control bus
        
        controls signal are sent
        
        instruction will be send from memory to processor
      - the processor
        
        made up of billions of transistors
        
        combined to make logic gates
        
        very fast
        
        fetch decodes and executes
    - - keyboard,mouse,printer
      - secondary storage
    - - computers built iinto a machine
        
        washing machine
  - - - performs fetch, decode and execute
      - contains clock for keeping time
      - Uses address bus to acess memory
    - - does maths
    - - program counter
        
        stores the location of the next instruction
      - memory address register
        
        stores the current address of data/instruction
      - Instruction register
        
        Stores the instruction ready to be decoded
      - Accumulator
        
        stores the result of the alu
  - - - measured in hertz
    - - stores fast instructions
- - - - Encryption
        
        Scrambles data that has to be decrypted to be readable, usually a key is used
      - Defragmentation
        
        Reorganises files to put the fragments back together
      - Data compression
        
        Software that reduces the size of a file to lower disk space
      - Back up software
        
        Takes up a copy of files to prevent data loss
  - - - This translates commands from the operating systems into hardware specific commands the peripheral understands
    - - Provides different users to login
    - - How folders and files are presented in a computer
      - files dont exist
      - As files are saved and deleted the hard disk will become fragmented
- - - - For
        
        people cant afford it
        
        doesnt hurt anyone
        
        the creators should protect it
        
        Everyone is doing it
      - against
        
        Its stealing
        
        It costs them to make it
        
        Its illegal
    - - For
        
        Children use it
        
        It has illegal content
      - against
        
        Freedom of speech
        
        Its too large
        
        Parents should take responsibility
    - - for
        
        Could save lives
        
        If you have nothing to hide its fine
        
        help disabled people
      - against
        
        May be using our data
        
        We are entitled to our privacy
  - - - Data should be relevant
      - Must be secured
      - Must be only used for the purpose specified
      - Users have the right to access the data
    - - You cant access any unathorised data
      - You cant access with the intent to commit further offences
      - You cant access with the intent to modify data (viruses)
    - - You cant copy,modify or distribute copyrighted material without permission
    - - A way to grant copyright permission to creative work
    - - Provides the public with access to information held by public authorities
      - Members of public can request
      - They must publish this data
- - - - Sending emails pretending to be someone else
      - Social engineering
      - Protection
        
        Staff training
    - - A trail and error method of attempting passwords
      - Protection
        
        better passwords
        
        2 factor authentication
        
        Progressive delays
    - - Flooding a server with traffic so it cant process requests
      - Protection
        
        Strong firewall
        
        Packet filters on routers
        
        Well configured web server
    - - Interception of data using a packet sniffer
      - Physical interception because user has left computer on or password written down
      - Protection
        
        Encryption
        
        Virtual private networks
        
        Train staff
    - - A technique used to view or change data in a database by inserting code
      - Protection
        
        Good validation on input boxes
        
        Using parameter queries
        
        Penetration testing