System Architecture - GCSE Computer Science OCR

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  • Chapter 1 - Systems Architecture
    • The CPU
      • Components
        • Registers
          • MAR
            • Holds address of instruction to be fetched
              • About instructions that are being fetched into CPU
                • Temporarily holds instructions after being fetched
          • MDR
            • Temporarily holds instructions after being fetched
            • Inside ALU
          • PC
            • Holds address of next instruction to be processed
            • Counts number of cycles - each function adds 1
          • CIR
            • Holds current instruction to be executed
              • Both about instruction being processed in the CPU
                • Holds address of next instruction to be processed
            • Inside CU
              • PC
                • Counts number of cycles - each function adds 1
              • MAR
                • Holds address of instruction to be fetched
                  • About instructions that are being fetched into CPU
            • Accumulator
              • Stores result of the previous calculation
              • Inside ALU
          • CU
            • Controls sequence of execution
            • Decodes instrucions
            • Regulates pulses and processor timing
            • Sends and receives control signals between other hardware
          • ALU
            • Logical operations
              • AND
              • OR
              • NOT
            • Shifting bits left or right by n places
            • Arithmetic operations
      • Function of the CPU
        • Fetch-Execute Cycle
          • Fetch
            • CPU requests address of instruction
              • MAR holds address from main memory
                • MDR holds data from main memory
                  • Data from MDR transferred to CIR
                    • PC holds address of the current instruction
          • Decode
            • CIR's instruction is decoded
          • Execute
            • Executed
    • Subchapters
    • Overarching ideas
    • Key information
    • Also key information
    • Linking ideas

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