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• 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 operations needed to execute instructions
• Control Unit

  Coordinates the fetch-execute cycle and decodes instructions
• Cache

  Small, fast memory that holds frequently accessed items (instructions, data, addresses)
• Special purpose registers

  • Memory Address Register (MAR)
  • Memory Data Register (MDR)
  • Program Counter
  • Accumulator
• Fetch-Execute Cycle

  1. Fetch instruction from memory using Program Counter

  2. Decode instruction in Control Unit

  3. Execute instruction, often using ALU and fetching data
• Clock speed

  Rate at which the fetch-execute cycle is carried out (in GHz)
• CPU performance factors

  • Clock speed
  • Number of cores
  • Cache size
• Embedded systems

  Computers built into other devices, usually with a single purpose
• RAM

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

  Non-volatile memory, contains startup program
• Hard Disk Drives (HDDs)


  • Large capacity, reliable, but fragile and noisy
• Optical Discs


  • Portable, reliable, but easily damaged
• Solid State Drives (SSDs)


  • Fast, durable, but more expensive
• Binary units


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


  1. Carry 1 to next column for 1+1

  2. Carry 1 for 1+1+1
• Overflow errors can occur when the result of a binary operation exceeds the available storage space
• Character sets


  Groups of codes representing characters (e.g. ASCII, Unicode)
• Pixels


  Blocks of color that make up an image
• Image resolution


  Number of pixels (width x height)
• Color depth


  Number of bits per pixel
• Metadata

  Data about data, used to recreate an image
• Analog to digital conversion


  Sampling the amplitude of a sound wave at regular time intervals (sample rate)
• Bit depth


  Number of bits used to represent each sound sample
• Compression


  Reducing file size, either lossless or lossy
• Network types


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


  Clients request data from servers, which have central control
• Peer-to-peer network


  Devices can act as both clients and servers, with no central control
• Network topologies


  • Star
  • Mesh
• Star topology


  Central device that all other devices connect to, easy to add new devices
• Mesh topology


  Direct connections between all devices, complex but high performance
• Network hardware


  • Wireless Access Point (WAP)
  • Router
  • Network Interface Card (NIC)
  • Switch
• MAC address


  Unique hardware address used to identify devices on a network
• Bandwidth


  Maximum data transfer rate, shared between all devices on a network
• MAC address


  A unique address worldwide specific to hardware that enables you to pinpoint the correct device on your network
• Switch


  • A bit like a router but within a single network, uses MAC addresses to make sure packets go to the correct destination
• Bandwidth


  The maximum amount of data that can be transferred at any given time
• Adding more devices to a network

  Requires sharing the limited bandwidth, leading to slower transmission and more collisions
• IP address


  Roughly tells us where a device is geographically, in the world