AQA COMPUTER SCIENCE A LEVEL - COMPUTER ORGANISATION AND ARCHITECTURE EXAM WITH

AQA COMPUTER SCIENCE A LEVEL -
COMPUTER ORGANISATION AND
ARCHITECTURE EXAM WITH ALL
ANSWERS CORRECT




What are the steps in the fetch part of the fetch-decode execute cycle (in words)? -
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correct answer-1. The contents of the Program Counter are copied onto the MAR
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2. The contents of the MAR are transferred to the memory through the address bus
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where it receives a control signal from the control unit indicating a memory read
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3. The contents of the memory at the received address are transferred to the MBR
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through the data bus
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At the same time, the PC is incremented by 1
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4. The contents of the MBR are copied onto the CIR
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What are the steps in the fetch part of the fetch-decode execute cycle (in register
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transfer notation)? - correct answer-1. MAR ← [PC]
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2. MBR ← [Memory]addressed
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PC ← [PC] + 1
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3. CIR ← [MBR]
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What are the steps in the decode and execute parts of the fetch-decode execute
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cycle? - correct answer-1. Control unit splits the instruction in the CIR into opcode and
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operand
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, 2. Control unit uses opcode to identify the instruction being executed and the part of
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the processor executing the instruction
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3. Control unit generates necessary control signals for execution
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4. Certain actions are performed depending on the instruction
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What are the possible actions the processor can take in the execute part of the fetch-
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decode execute cycle? - correct answer--Jump/Branch instruction -> PC is updated
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-Data is required -> Memory or I/O read is issued
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-Arithmetic/Logic operation -> ALU calculates results and stores in register(s) and the n n n n n n n n n n n



status register updates to show overflow or carry
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What happens in the interrupt part of the fetch-decode execute cycle if an interrupt
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signal of higher priority has been received by the processor? - correct answer-1. The
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current process being executed is suspended and the current values of the registers
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are pushed to the system stack
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2. The appropriate Interrupt Service Routine is found and called to handle the interrupt
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3. After the interrupt has been serviced, the original values of the registers are
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retrieved from the stack and execution continues with the instruction addressed by the
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PC
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What is an interrupt? - correct answer-A signal sent to the processor that suspends
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execution of the current process until the interrupt is handled with an Interrupt Service
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Routine (ISR)
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What sends interrupts? - correct answer-Hardware devices and software programs
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Why do the register contents have to be pushed to the system stack when an interrupt
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is received? - correct answer-To save the volatile environment as the registers are
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going to be overwritten so the values would be lost otherwise
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What does the use of interrupts allow a processor to do? - correct answer-Multitask
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(using time slices and timer interrupts)
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What is hardware? - correct answer-The physical components of a computer system
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In brief, what does the processor do? - correct answer-Processes data and
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ninstructions by fetching, decoding and executing instructions in the fetch-decode-
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execute cycle n




What is the job of the control unit in the processor? - correct answer-Sends control
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signals and manages the fetch-decode-execute cycle in addition to the processor as a
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whole
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What is the job of the Arithmetic Logic Unit in the processor? - correct answer-
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Performs calculations on data it is given such as addition, subtraction or shifting
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