computing

• 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
• Fetch-Execute Cycle


  1. Fetch instruction from memory using Program Counter

  2. Decode instruction

  3. Execute instruction, possibly 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, with one specific purpose
• Types of storage


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


  Volatile memory, contents lost when power is off
• ROM


  Non-volatile memory, contains startup program
• Hard disk drives


  • Reliable, large capacity, but fragile and noisy
• Optical discs


  • Portable, reliable, but easily damaged
• Solid state drives


  • Fast, durable, but more expensive
• Binary units


  • Bit
  • Nibble
  • Byte
  • Kilobyte
  • Megabyte
  • Gigabyte
• Converting between binary, hexadecimal and decimal


  1. Use place value tables

  2. Binary: each column is 2x previous

  3. Hexadecimal: each column is 16x previous
• Binary addition


  Carry 1 to next column for 1+1, 1+1+1
• Binary shifts


  1. Left shift: double the number

  2. Right shift: halve the number
• Overflow error can occur if result is too large for storage
• Character sets


  ASCII: 8-bit, 256 characters

  Unicode: 16-bit+, supports many languages
• Pixels


  Smallest unit of an image, with a color depth
• Metadata


  Data about data, stored with the image/sound
• Sample rate


  Number of sound samples taken per second
• Bit depth


  Number of bits per sound sample
• Compression


  Lossy: reduces quality, lossless: maintains quality
• Network types


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


  Clients request from servers, servers respond
• Peer-to-peer network


  Devices can act as both clients and servers
• Network topologies


  • Star
  • Mesh
• Star topology


  Central device all others connect to, easy to add devices
• Mesh topology


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


  • Wireless access point
  • Router
  • Network interface card
  • Switch
• MAC address


  Unique hardware address for network devices
• Bandwidth


  Maximum data transfer rate, shared between devices
• 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