igcse cie computer science

• Binary


  The number system used by computers to represent all forms of data
• Number systems


  • Denary (base 10)
  • Binary (base 2)
  • Hexadecimal (base 16)
• Converting between number systems

  1. Denary to binary

  2. Denary to hexadecimal

  3. Hexadecimal to binary
• Hexadecimal


  A beneficial method of data representation as it is easier for humans to understand than binary
• Overflow


  An error that occurs when a value outside the predefined limit of a computer or device should be returned
• Logical binary shift


  1. Perform logical left shifts

  2. Perform logical right shifts

  3. Perform multiple shifts
• Two's complement

  A way to represent positive and negative 8-bit binary integers
• Character sets


  Used to represent text, including ASCII and Unicode
• Unicode


  Allows for a greater range of characters and symbols than ASCII, including different languages and emojis
• Sound representation


  Sampled at a sample rate and sample resolution
• Image representation


  Represented as a series of pixels with a resolution and colour depth
• Data storage units


  • bit
  • nibble
  • byte
  • kibibyte (KiB)
  • mebibyte (MiB)
  • gibibyte (GiB)
  • tebibyte (TiB)
  • pebibyte (PiB)
  • exbibyte (EiB)
• Data compression


  Reduces the size of a file, either losslessly or lossily
• Packet switching


  1. Data is broken down into packets

  2. Each packet could take a different route

  3. A router controls the route a packet takes

  4. Packets may arrive out of order

  5. Once the last packet has arrived, packets are reordered
• Data transmission methods


  • Serial
  • Parallel
  • Simplex
  • Half-duplex
  • Full-duplex
• USB interface


  Used to transmit data
• Error detection


  Needed to check for errors after data transmission, which can occur due to interference
• Error detection methods


  1. Parity check (odd and even)

  2. Checksum

  3. Echo check

  4. Check digit

  5. Automatic repeat query (ARQ)
• Encryption


  Needed to transmit data securely, using symmetric or asymmetric encryption
• Central Processing Unit (CPU)


  Processes instructions and data that are input into the computer
• Microprocessor


  A type of integrated circuit on a single chip
• Fetch-Decode-Execute (FDE) cycle


  How instructions and data are fetched, decoded and executed in a CPU with a Von Neumann architecture
• CPU components


  • Arithmetic Logic Unit (ALU)
  • Control Unit (CU)
  • Registers (PC, MAR, MDR, CIR, ACC)
  • Buses (address, data, control)
• CPU performance factors


  • Number of cores
  • Size of cache
  • Speed of clock
• Instruction set


  A list of all the commands that can be processed by a CPU
• Embedded system


  Used to perform a dedicated function, different to a general purpose computer
• Input devices


  • Barcode scanner
  • Digital camera
  • Keyboard
  • Microphone
  • Optical mouse
  • QR code scanner
  • Touch screen (resistive, capacitive and infra-red)
  • 2D and 3D scanners
• Output devices


  • Actuator
  • DLP projector
  • Inkjet printer
  • Laser printer
  • LED screen
  • LCD projector
  • LCD screen
  • Speaker
  • 3D printer
• Sensors


  • Acoustic
  • Accelerometer
  • Flow
  • Gas
  • Humidity
  • Infra-red
  • Level
  • Light
  • Magnetic field
  • Moisture
  • pH
  • Pressure
  • Proximity
  • Temperature
• Primary storage


  The main memory of a computer system
• Sensors


  • barcode scanner
  • digital camera
  • keyboard
  • microphone
  • optical mouse
  • QR code scanner
  • touch screen (resistive, capacitive and infra-red)
  • two-dimensional (2D) and three-dimensional (3D) scanners
• Actuators


  • actuator
  • digital light processing (DLP) projector
  • inkjet printer
  • laser printer
  • light emitting diode (LED) screen
  • liquid crystal display (LCD) projector
  • liquid crystal display (LCD) screen
  • speaker
  • 3D printer
• Types of sensors


  • acoustic
  • accelerometer
  • flow
  • gas
  • humidity
  • infra-red
  • level
  • light
  • magnetic field
  • moisture
  • pH
  • pressure
  • proximity
  • temperature
• Primary storage


  Directly accessed by the CPU
• Secondary storage


  Not directly accessed by the CPU and is necessary for more permanent storage of data
• Magnetic storage


  • Uses platters which are divided into tracks and sectors. Data is read and written using electromagnets
• Optical storage


  • Uses lasers to create and read pits and lands
• Solid-state (flash memory) storage


  • Uses NAND or NOR technology. Transistors are used as control gates and floating gates
• Virtual memory


  Pages of data are transferred between RAM and virtual memory when needed
• Cloud storage


  Can be accessed remotely in comparison to storing data locally. Physical servers and storage are needed to store data in cloud storage