Topic 1: Hardware and communication

• The control unit directs the flow of data and instructions between the CPU and other devices
• The program counter (PC) holds the data or instruction that is to be processed next
• The Current instructions register (CIR) stores the details of instructions that are currently being executed.
• The ALU performs all the arithmetic and logical calculations in the CPU.
• The MAR holds the memory location of data that is to be accessed.
• The MDR holds the data instructions that just came in or about to depart for the main memory.
• The results of calculations carried out by the ALU are temporarily stored in the Accumulator
• Busses connects different parts of the CPU
• Level 1 cache is extremely fast but extremely small (between 2-64KB) located very close to the processor
• • The cache memory is integrated directly within the CPU
  • Cache memory stores program instructions that are frequently used.
  • Cache memory also stores the immediate results of calculations.
  • The cache memory helps to solve problems by acting as a ‘middleman’ between the processor and the memory.
  • Frequently used data and instructions are copied into the cache and when the processor needs this data, it can be retrieved much faster than if it were stored in RAM
  • Cache memory is expensive compared to RAM
  • Cache memory is faster than the RAM
  • Cache memory is smaller than the RAM and is also volatile
• A multicore processor is a single chip containing two or more independent processing units.
• In parallel processing, two or more processors work together to handle a single task
• A computer is an electronic device that takes inputs, processes it and produces a desired output
• Fetch stage

  • The Program counter is checked as it holds the next instructions that is to be executed
  • The instructions are then copied into the MAR
  • The instructions are then sent to the main memory using the address bus
  • The control unit then sends a read signal to the main memory using the control bus
  • The contents stored in the MAR are then sent along the data bus to the MDR.
• Decode stage

  • The contents in the MDR is then copied into the CIR
  • The instructions in the CIR is then decoded by the decode unit
  • The new instructions are then stored in the accumulator
• Factors affecting the choice of secondary storage

  • Capacity: The amount of data that can be stored
  • Durability: How much damage it can take before it damages
  • Portability: How easy is it to move from one place to another
  • Speed: How quickly the user can access the data stored on it
• Functional characteristics of hard drives

  • A common speed for hard drives is 7200RPM
  • Typical capacity: 500MB-4TM
  • Typical uses: Storing programs, Storing the operating system, server backup
  • Can be used as a hybrid with SSD
  • Hard drives are a magnetic medium that store data on a platter
  • As the disk spins, the arm travels across the disk
• Functional characteristics of SSD'S

  • Non-Volatile
  • Non-moving parts
  • Typical capacity: 500MB - 4TB
  • Typical uses: Storing the operating system, Storing programs, Server backup.
• Optical storage devices functional characteristics (DVD)

  • They work by using lasers to store data
  • Typical capacity: 650MB - 25BG
  • Typical uses: Storing movies, Storing music
  • Indentations and their absence create pits and lands
• Functional characteristics of Blu-ray drives

  • Typical capacity: 25GB to 50GB
  • Typical uses: Storing movies and music
  • Non-volatile
  • Blu-ray data is stored in two layers