computer science paper 1

• 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
• Types of storage

  • Primary (RAM, ROM)
  • Secondary (Magnetic, Optical, Solid-state)
• RAM


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


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


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

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

  • Fast, durable, but expensive
• Binary units

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


  1. Carry 1 to next column if 1+1=0

  2. Carry 1 if 1+1+1=1
• Binary shifts


  1. Left shift doubles the number

  2. Right shift halves the number
• Overflow error


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


  • ASCII
  • Unicode
• Pixel


  Smallest block of color in 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 image
• Sample rate


  Number of sound samples taken per second
• Bit depth


  Number of bits per sound sample
• Lossy compression


  Deletes part of the file to reduce size
• Lossless compression


  Rearranges the file to be more efficient without deleting data
• Network types


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


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


  Devices can act as both clients and servers, connect independently
• Network topologies


  • Star
  • Mesh
• Star topology


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


  Devices connect directly to each other, complex but high performance
• Network hardware


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


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


  Maximum amount of data that can be transferred at a given time
• 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