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
• 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
• 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 if 1+1, carry 1 if 1+1+1
• Binary shifts


  1. Left shift: double the number

  2. Right shift: halve the number
• Overflow errors can occur if the result of a binary operation is too large to fit in the available storage
• Character sets


  ASCII: 8-bit, 256 characters

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


  Smallest block of colour in 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
• Digital sound


  Samples of analog sound wave amplitude at regular time intervals (sample rate)
• Bit depth


  Number of bits per sound sample
• Compression


  Reducing file size, can be lossy or lossless
• Network types

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


  Clients request data from servers
• Peer-to-peer network


  Devices can act as both clients and servers