Computer Science

• The CPU is the central processing unit, it carries out program instructions using data
• Components inside the CPU

  • ALU (Arithmetic Logic Unit)
  • Control Unit
  • Cache
  • Registers
• ALU

  Carries out maths and logic needed to execute instructions
• Control Unit

  Coordinates the fetch-execute cycle and decodes instructions
• Cache

  Small, fast memory that holds frequently accessed items
• Special purpose registers

  • Memory Address Register (MAR)
  • Memory Data Register (MDR)
  • Program Counter
  • Accumulator
• MAR

  Holds the address in memory where data/instructions are fetched from or written to
• MDR

  Holds the actual data/instructions that have been fetched from or will be written to memory
• Program Counter

  Holds the address of the next instruction to be fetched
• Accumulator

  Holds the results of ALU calculations
• Von Neumann Architecture

  The structure of a CPU that carries out the fetch-execute cycle
• Fetch-Execute Cycle

  1. Fetch instruction from memory using Program Counter

  2. Decode instruction in Control Unit

  3. Execute instruction, usually using ALU and data from MDR
• Clock speed

  The rate at which the fetch-execute cycle is carried out, measured in GHz
• CPU Characteristics

  • Clock speed
  • Number of cores
  • Cache size
• Increasing clock speed, cores, or cache size will increase CPU performance
• Embedded systems

  Computers built into other devices to perform a specific function
• Types of computer storage

  • Primary (RAM, ROM)
  • Secondary (HDD, SSD, optical)
• RAM

  Volatile memory, contents are lost when power is turned off
• ROM

  Non-volatile memory, contains the program that boots up the computer
• Virtual memory

  Part of secondary storage used as an extension of RAM when it is full
• Types of secondary storage

  • Magnetic (HDD)
  • Optical (DVD)
  • Solid state (SSD)
• Magnetic storage (HDD)

  • Large capacity, reliable, but fragile and noisy
• Optical storage (DVD)

  • Portable, reliable, but easily damaged
• Solid state storage (SSD)

  • Fast, durable, but expensive
• Binary units

  • Bit
  • Nibble
  • Byte
  • Kilobyte
  • Megabyte
  • Gigabyte
  • Terabyte
• Binary shifts


  1. Left shift: double the number

  2. Right shift: halve the number
• Character encoding standards

  • ASCII
  • Unicode
• ASCII

  1. bit character codes, only supports 128 characters
• Unicode

  16-bit or more character codes, supports thousands of characters
• Pixel

  The smallest unit of an image
• Image resolution

  The number of pixels in an image, usually expressed as width x height
• Color depth

  The number of bits used to represent the color of each pixel
• Metadata

  Data about data, additional information stored with an image or sound file
• Sample rate

  The number of samples of sound amplitude taken per second
• Bit depth

  The number of bits used to represent the amplitude of each sound sample
• Compression

  Reducing file size, can be lossy (quality reduced) or lossless (no quality loss)
• Network types

  • LAN (Local Area Network)
  • WAN (Wide Area Network)
• Client-server network

  Devices are either clients (request data) or servers (provide data)
• Peer-to-peer network

  Devices can act as both clients and servers, connecting directly
• Network topologies

  • Star
  • Mesh