1.1 System architecture

  • Created by: HMajid198
  • Created on: 21-08-20 12:34
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  • System architecture
    • CPU
      • Process data and instructions
      • Controls the rest of the computer
      • Controls hardware components
    • Von Neumann architecture
      • MAR - holds address of current instruction that is to be fetched or the address in memory in which data is to be transferred
      • MDR - Holds contents found at address held in MAR or data which is to be transferred to primary memory
      • PC - (program counter) holds memory address of next instruction to be fetched from primary memory
      • ACC - (accumulator) holds data being processed and the result of processing
      • Data and instructions in binary, stored in primary memory, instructions fetched one at a time in order and instruction is decoded and executed before fetching next
    • Common CPU components
      • Arithmetic logic unit - (ALU) performs arithemic and logic calculations
      • Control unit - (CU)  manages instructions in the CPU
      • Cache - very fast RAM in the CPU (easily accessible) - temporarily stores data likely to be re-used
      • Clock - sends out regular pulses to synchronise the computer's components
      • Cores - processing unit within the CPU each capable of fetching, decoding and executing its own instructions
    • Fetch decode execute cycle
      • 1. Memory address held in the program counter is copied into the MAR
      • 2. Address in the program counter increases by 1 (now holds address of next instruction)
      • 3. Processor sends a signal along the address bus to the memory address held in the MAR
      • 4. Instructions/ data held in that address are sent along the data bus to the MDR
      • 5.  Instruction/ data held in MDR is copied into the CIR
      • 6. Instructions/ data held in the CIR are decoded and executed - results are stored in the ACC
    • CPU performance
      • Clock speed - number of pulses the CPU's clock processes generates per second
        • Can be sped up by the user (overclocking) - can cause long term damage and can cause overheating
        • More pulses per second = more FDE cycles can be performed
      • Cache size - bigger the cache size, the less time the processor has to wait
      • Number of cores - the more cores in a CPU, the greater the number of instructions that can be processed in a given space of time
    • Embedded systems
      • Embedded system - a small computer that forms part of a larger system - controls the device and allows a user to interact with it
      • Examples: central heating, calculators, dishwashers, digital watches
      • Not programmable by a user but software can be upgraded
      • Advantages: cheaper to design due to limited features, require less power and do not need much processing power


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