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Computer Science Master - Coggle Diagram

- - - - RAM
        
        RAM stands for Random Access Memory which stores a copy of all the programs that the computer is using. This allows the CPU to access them quickly so is called IAS or Immediate Access Store. RAM is a lot quicker than the Hardrive
        
        It is called Volatile Memory because when RAM loses power all the data is lost and cannot be retrieved
        
        IAS
        
        It uses DRAM which is slower the SRAM and constantly needs to be refreshed however it is cheaper and requires less transistors and capacitors. It is the more common type so you have more in a computer
        
        Cache
        
        It uses SRAM which is faster the DRAM and does not constantly need to be refreshed however it is more expensive and requires 6 times transistors and capacitors. It is the less type so you have less in a computer
      - ROM
        
        The ROM or Read Only Memory is the storage that holds the BIOS and Bootstrap program.
        
        The memory is non-volatile so does not get lost when no power is running through it
        
        When the computer is turned on the BIOS or Basic Input Output System which runs a POST(Power On Self Test) check to see if the compute is healthy. If it is then the bootstrap program is loaded from ROM to RAM. The bootstrap locates the OS in the Hardrive and it is loaded into RAM. The OS takes over and finds the boot files. These include all the user customised options such as wallpaper
      - Virtual Memory
        
        It is when the RAM gets to full so allocates a part of the Hardrive to be used like RAM. The Computer however has to swap in and out programs when they need to be used.
        
        Because the RAM is faster than the Hardrive their is delay between the swapping. If the computer has to swap out to much, it will slow down and could crash all together. This is called Disk Thrashing
      - Flash Memory
        
        Flash Memory also known Solid State Devices. This is because they do not have any moving parts. They are completely electronic
        
        These include SD cards, ROM Chips, Pen Drives
        
        They do not wear out very easily
        
        Very Fast
        
        Uses very little power
  - - - Secondary Storage
        
        Secondary Storage is crucial if you want to access something later. Some examples it saves the Operating System or your contacts, photos and videos.
      - Data Capacity/Data Capacity Calculation
        
        Byte
        
        8 bit
        
        Nibble
        
        4 bit
        
        Bit
        
        Kilobyte
        
        Megabyte
        
        Gigabyte
        
        Terabyte
        
        Petabyte
        
        Exabyte
        
        Zettabyte
        
        Yottabyte
        
        Each ine increases by 2^10 or 1024
        
        For example one megabyte is equivalent to 1024 kilobyte
        
        Let'ts say a bool has 90,000 words and each word takes up 7 characters each character is 2 bytes. This means it would be 2x7x90,000 = 1,260,000 Bytes. Covert to = KB so divide by 1024 to get 1230 KB
      - Types of Storage
        
        Optical -- A lazer burns a pattern into the surface of the disk. Another lazer skims over the disk, if the dot is reflected differently if there is or ins't a dot there. That's how the data is read
        
        Speed
        
        Slower read times
        
        Portability
        
        Easy to distribute
        
        Reliability
        
        Not very reliable
        
        Durability
        
        Easily scrached and damaged
        
        Cost
        
        Relatively Cheap
        
        Capacity
        
        Decent Capacity
        
        Magnetic - When the tape is magnetised it kept there magnetism. The tape is divided into million of tiny segments. Being magnetised and being demagnetised represents binary
        
        Durability
        
        Very durable if treated correctly. Can be damaged by dropping or magnetic fields
        
        Portability
        
        Not overly portable
        
        Capacity
        
        Largest Capacity
        
        Cost
        
        Cheapest type
        
        Reliability
        
        Great for archiving if well kept
        
        Speed
        
        Slowest type unless in a internal hard drive
        
        Solid State -- They use a electrical circuits where semi-conductor material where a pattern of on/off switchs
        
        Durability
        
        Very Durable as it has no moving parts
        
        Portability
        
        Portable in small devices
        
        Capacity
        
        Medium Capacities
        
        Cost
        
        Most expensive
        
        Reliability
        
        It has a limited number of read and write cycles which limits its useful time, However the SS are usually very reliable.
        
        Speed
        
        Fastest type of storage
  - - - Types of Networks
        
        LAN
        
        Local Area Network - Collection of computers over a small geographical area that are connected and managed centrally
        
        WAN
        
        Wide Area Network - Collection of computers over a widegeographical area that are connected and managed centrally
        
        VPN
        
        Virtual Private Network - Not a physical network but a part of the internet which is en
        
        Disadvantages
        
        More expensive to setup and maintain
        
        Can be hacked and viruses easily spread
        
        If one part of the network fails, the whole network could go down
        
        Advantages
        
        Can communicate with each other
        
        Share resources easier
        
        Updates and software applications can be distributed atomatically
        
        Data only needs to be backed up on central sever
        
        Files can be accessed form any computer
        
        Security can be managed by the network manager. Virus Protection and patches shared centrally
    - - A Modem works by taking the digital signals from a computer and turn them into analogue signals. These are passed down a phone line where another modem picks them up and turns them back into digital.
      - A Broadband router combines a switch and a modem. The router allows many computers to connect to the broadband network. It also has a admin area
    - - That means that the raw sound or movie file has a maths formula applied to it (called a 'codec', short for coder / decoder) so that the raw file gets squashed or 'compressed'. The file then becomes much smaller in size so it can be downloaded and streamed more quickly.
    - - Encryption
        
        Encrypting data scrambles the data with a maths formula or "key" which turns the data into seemingly unrelated characters. Encrypted data is called Cipher text and un-encrypted is called plain text
        
        The different types are WAP, WAP2 and WEP however this should not be used as it is weak
      - Access Levels
        
        User access levels control parts of network different groups can access. High authority have higher access levels allowing them to see more sensitive data. They also have the ability to change people's access levels.
      - Passwords
        
        Password are the most common way to prove your identity. They should be strong with a range of characters and should be changed regularly
    - - Client Server Network
        
        An expensive network to set up as more hardware needs to be purchased
        
        Files can be automatically backed-up to a central location from each computer
        
        It has a central computer that provides all the services to the network
        
        Peripherals on the network can be shared
        
        Most commonly found in larger offices and orgaisations
        
        Advantages
        
        Backups easier and Updates easier
        
        Security easier to manage
        
        Keep track of files
        
        Very Reliable
        
        Disadvantage
        
        Expensive
        
        Requires Specialist
        
        Server Dependent
        
        May become overloaded
      - Peer-to-Peer Network
        
        Most commonly found in a home or small office
        
        Computers are networked together
        
        Each computer on the network needs to be ,maintained separately
        
        Peripherals on the network can be shared
        
        A cheaper network to set up as less hardware needs to be purchased
        
        Advantages
        
        Easy to maintain
        
        Cheap
        
        No dependence
        
        Disadvantages
        
        Backups and Updates harder
        
        Security Harder
        
        Less reliable
        
        Harder to keep track of files
    - - A DNS is a server that when a domain name is searched in the URl it looks up that domain name on its database and finds the matching IP Address and forwards the request on using that IP address
  - - - Ethernet
        
        Communication protocol -Defines rules
        
        Medium - Type of cable, CAT 5 or fibre optic
        
        Segment - A part of the Ethernet that uses the same cable
        
        Node - Any hardware that connects to a segment
        
        Frame - A burst a data packets from node
      - Topologies
        
        Star
        
        Star is where all the devices are connected to a central hub/switch
        
        A hub does not discriminate but the switch is an upgraded version and does
        
        Usually the choice for schools or offices
        
        Advantages
        
        Easily upgraded
        
        Easy Setup and troubleshoot
        
        Reliable
        
        Good Security
        
        Disadvantages
        
        Cost is high
        
        If hub/switch goes down, so does the network
        
        Performance depends on hub/switch
        
        Require technical expertise
        
        Mesh
        
        Is where all the nodes are connected to each other or most of them. Usually the node they exchange the most data
        
        Advantages
        
        Relatively Fast - No middle man
        
        Can handle high traffic
        
        Keeps going if one breaks
        
        Disadvantages
        
        Lots of cable males more robust but expensive
        
        Complex and Matience costs are hugh
      - TCP/IP model
        
        Application - What user interacts with
        
        Transport - Opens link between nodes
        
        Network/Internet - Finds the best route for the message across different networks
        
        Link - How the physical hardware NIC works with the OS drivers to send the message
      - The frequency is the number of times the EM waves are sent in a second
      - Network Protocols
        
        A protocol is an agreed way of communicating
        
        They must agree on the format the data will be sent in
        
        Organised in models
        
        Transmission Control Protocol is the other part of the Internet protocol suite which deals with the order of the transferred data as well as controlling traffic on the internet. Opens the link between nodes
        
        IP or the Internet Protocol and is part of the Internet protocol suite for relaying data packets through different networks. Finds routes
        
        SMTP
        
        Is about sending messages from nodes
        
        IMAP
        
        Is about receiving messages, however it saves a temporary copy of the message onto the node, stores the message on sever and synchronises across devices
        
        POP
        
        Downloads the message from sever to the single node and then deletes from the server
      - Tethering
        
        Tethering allows a phone with data access to setup a Wi-Fi hotspot for devices that can only use Wi-Fi. It has a name and password and they can gain access.
        
        They might use up your bandwidth very quickly and you will have to pay for more.
      - Packet Switching
        
        The email is split into equal sizes of data packets and sent across the internet in this case. Each package takes its own route to allow for the most efficient use of the bandwidth; finding the best path for itself, going from network to network.
        
        Each packet has: the address of the sender, destination address, packet number, packet reassembling information and a check sum for error detection.
        
        When a packet is received, a confirmation message is sent back to tell the computer to stop trying to send the message
      - Client-Server vs Peer-to-Peer
        
        A client-sever network is where all the computers on the network or clients connect to a central large powerful computer called a server which holds, stores and controls all the user's files
        
        All of the computers on the network have equal status (they are peers of each other). Each one can communicate with all of the others and each of them may have a role in helping to manage the whole network.
        
        For example, one computer could send a file to another computer and have it saved on that computer. A computer might send a file to be printed to another computer, which has a printer attached to it.
  - - - Data Interception - collecting or manipulating data
        
        Collecting
        
        Gathers data, e.g for blackmail
        
        Manipulating
        
        Changes data
        
        Data Theft - employee takes the confidential company information, deletes / copies
      - Malware describes a variety of intrusive software
        
        There designed to steal sensitive information, disrupt lives and create fake identities
        
        Virus - Attaches to files/application and cause a lot of damage. They change the contents of the hard drive and use up memory
        
        Trojan horses are similar to viruses hidden as seemingly innocent programs
        
        Worms can spread by themselves via vulnerable network connections. Self replicate, use authorised systems, taking up a lot of bandwidth
        
        Spyware - Gets access to the computer without the user knowing. Gathers data about personal information and habits, transmitting that data to unauthorised people
        
        Adware - Is software that cause adverts to pop up on your screen, using up memory and annoying the user
        
        Ransomware - Locks down and encrypts your files, then offered to be encrypted for money
    - - Use a different password for each account
      - Don't use a weak password
      - Don't write passwords down in insecure area
      - Use a password manager
      - Change them reguraly
      - Security
        
        Should be long
        
        Mix of numbers, upper and lower case, symbols
        
        Don't use names, dictionary words, dates or common passwords
        
        Substitutes letters with symbols
  - - - operating system - manages the hardware and provides UI
        
        Memory
        
        Data that is copied into memory is kept track, where it is things don't get overwritten
        
        Multitasking
        
        Defragmentation
        
        Retrieving files takes more processing so reduces performance
        
        Creates space and improves performance
        
        Peripherals
        
        Getting input and sending output
        
        Switching data between memory and disk
        
        device communicates with the OS via its own driver
        
        Print Buffer - A special area of memory in either the computer or printer
        
        Stores jobs, printer takes time to print
        
        Files
        
        Manages where on the disk files are written, where it is things don't get overwritten
        
        File transfer, move, copy, transfer
        
        User access rights
        
        Users and admins have different levels of access rights
        
        Saved for them
        
        User Interface Types
        
        GUI: Graphical User Interface
        
        Icons representing functions
        
        CLI: Command Line Interface
        
        Must be typed in text
        
        Interupt - signals sent that need immediate action
        
        Hardware interupt
        
        Software interrupt
        
        Encryption
        
        Transforms text so it can’t be read without knowing key to
        decode it
        
        Compression
        
        Reduces file size so more data can be stored on a disk
        
        Less bandwidth for streaming
        
        Backup
        
        Full
        
        Complete backup of everything
        independently of any other backup
        
        Takes more file space
        
        Incremental
        
        Backups everything new from last backup
        
        Requires multiple restorations to get everything back, less secure
  - - - General Data Protection Act 1998
        
        1) data must be processed fairly and lawfully
        
        2) data must be adequate, relevant and not excessive
        
        3) data must be accurate and up to date
        
        4) data must not be retained for longer than necessary
        
        5) data can only be used for the purpose for which it was collected
        
        6) data must be kept secure
        
        7) Not transferred outside the European Economic Area (EEC) without adequate protection
      - Computer Misuse Act 1990
        
        Unauthorised access to computer material
        
        Unauthorised access with intent to commit or facilitate a crime
        
        Unauthorised modification of computer material
        
        Making, supplying or obtaining anything which can be used in computer misuse offences
      - Copyright, Designs and Patents Act (1988)
        
        Copyright law protects owner of a creative work from having it illegally copied
      - Creative Commons Licensing
        
        Used when an author is willing to give people the right to share or use a work that they have created
        
        Can choose if it can be commercial or not
      - Open and Proprietary Source
        
        Open
        
        Disadvantages
        
        Often less polished
        
        Less technical support
        
        Less secure
        
        Advantages
        
        Cheaper
        
        Free
        
        Low development costs and quicker
        
        Closed
        
        Advantages
        
        'More professional'
        
        Better technical support
        
        More secure
        
        Disadvantages
        
        High development cost
        
        Strict deadlines
        
        Paid