whole paper 1 cs

• 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
• Secondary storage types


  • Hard disk drives: reliable, large capacity, fragile
  • Optical discs: portable, reliable, fragile
  • Solid state drives: fast, durable, expensive
• Binary units


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


  1. Carry 1 to next column for 1+1

  2. Carry 1 for 1+1+1
• Binary shifts


  1. Left shift: double the number

  2. Right shift: halve the number
• Overflow error


  Result takes up more storage space than is possible
• Character sets


  • ASCII: 8-bit, 256 characters
  • Unicode: 16-bit+, supports many languages
• 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, essential information to recreate the file
• Sound digitisation


  • Sampling amplitude at regular time intervals (sample rate in Hz)
  • Bit depth: number of bits per sample
• Compression


  • Lossy: deletes data, reduces quality
  • Lossless: rearranges data, no quality loss
• Network types


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


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


  Devices can act as both client and server
• Network topologies


  • Star
  • Mesh
• Star topology


  Central device, easy to add new devices
• Mesh topology


  Direct connections between all devices, high performance
• Network hardware


  • Wireless access point
  • Router
  • Network interface card (NIC)
  • Switch
• MAC address


  Unique hardware address to identify devices on a network
• 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
• IP address


  Roughly tells us where a device is geographically, in the world
• There are two types of IP addresses currently used - version 4 and version 6, with version 6 being much larger as version 4 ran out of combinations