GCSE Computing - Systems Architecture

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  • GCSE Systems Architecture
    • Components of the architecture
      • CPU
        • The purpose of the CPU is to carry out all of the processing in the computer. This is done by executing instructions.
        • It constantly follows the Fetch - Decode - Execute cycle.
          • The PC has the address of the next instruction to fetch. The value of the PC is copied to the MAR. The CU locates and fetches the data from the address. If it's data, it is placed in the MDR.
      • MAR
        • This stores the location of the data or instruction that is to be used by the MDR or the location of where data is to be stored.
      • MDR
        • This is the register that stores any data that is fetched or that is to be transferred to memory.
      • CIR
        • The current instruction register stores the most recently fetched instruction while it is waiting to be decoded and executed
      • PC
        • This register keeps track of the memory location for the next instruction.
      • ACC
        • The accumulator stores all of the results of calculations made by the ALU.
      • ALU
        • This unit carries out all of the calculations and logical decisions required by the program instruction.
      • CU
        • This unit is responsible for decoding the instruction and it sends out signals to control parts of the CPU and memory to execute these instructions.
      • RAM
    • Embedded Systems
      • An embedded system is a computer system that has a dedicated function as part of a larger device.
      • If a system has a digital element, it will have an embedded system.
      • Because it carries out only one task, it can be made very small and cheap. The software is uploaded during manufacturing and it is very hard to change them once they have been programmed.
      • Examples of embedded systems: DVD player in a car, timer on an oven and a GPS in a car.
    • Effects on Performance
      • Clock Speed
        • The higher the clock speed, the more instructions there will be processed per second.
      • Cache Size
        • The bigger the size of the cache, the more data there will be on the cache.
      • Number of Cores
        • The more cores there are in the computer system, the more instructions there will be processed per second/
    • Cache
      • Level 1 Cache: Located on the CPU, low capacity, high speed.
      • Level 2 Cache: Located on the CPU module, higher capacity that level 1 cache, slower than level 1 cache.
      • Level 3 Cache: Located on the motherboard, high capacity, slow speed.
    • Busses
      • Data Bus
        • This bus carries the data between the CPU and the memory.
      • Control Bus
        • This bus carries control signals around the CPU and memory.
      • Address Bus
        • This bus carries the memory addresses for the locations to be read or written to.


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