GCSE Computer science theory

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  • Computer science theory
    • Programming  languages
      • Machine code
        • A low level language that only computers understand
          • Displayed in binary
      • High level languages
        • Uses English and mathematical symbols - humans are able to understand this language
      • Binary
        • The only language computers understand
        • Binary can be used to represent all data types on a computer e.g. Images, Sound
          • Binary addition rules
            • 0+0=0
            • 1+0=1
            • 1+1=0    carry 1
            • 1+1+1= 1 Carry the 1
        • Binary to Hexadecimal
          • 1. Split the bits it to two sets of 4
          • 2. Add in the column headings
          • 3. Merge the output and find the corresponding hexadecimal value
      • Data conversions
        • 8 bits in a byte
        • Kilobyte = 1024 bytes
        • Gigabyte = 1024 MB
        • Megabyte = 1024 KB
        • Terabyte = 1024 GB
      • Data compression
        • Lossy
          • The file is compressed and some data is permanently lost along with some of the quality
        • Lossless
          • The file is compressed but the quality remains the same, the original file can be brought back if desired
      • Encryption
        • Data is more secure
          • Those who are meant to read a message can because they have the 'Key'
      • ASCII
        • Character representation
          • Each character has a decimal/ deanery  value which has a binary value
    • The internet
      • The internet
        • A global network any computer can join
          • Data is sent and received when you...
            • Visit a web page
            • Send an email
        • A WAN - Wide Area Network
        • IP addresses help computers find each other like a post code
          • With out an IP address information would never end up where it is needed
      • Protocols
        • A set of rules agreed about the internet
        • Protocol layers
          • Application
            • Provides access to email files and websites across an IP network
              • FTP, HTTP, POP, IMAP, SMTP
          • Transport
            • Devides massages into packets
              • TCP, UDP
          • Internet
            • Manages the addresses of sources and finds their destinations
              • IP
          • Link
            • Transmits and receives data through cables
              • ETHERNET, Wi-Fi
      • Topologies
        • Bus
          • All work stations are connected and joined to one cable (The bus)
        • Ring
          • Signals travel around the ring in one direction and each device receives each packet
          • Each device is connected two other devices
        • Star
          • Each individual device is attached to a central point
          • Data is sent to the  device which put in the request
      • Networks
        • A group of computers and other devices connected together
        • How is information protected??
          • Encryption
          • Firewalls
          • Passwords
        • Network Security
          • Protects data from threats
          • Keeps information confidential
          • Ensures data remains in the right hands

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