Aqa Computer Science A Level - n n n n n
Computer Organisation And n n n
Architecture Exam With All Answers
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Correct n
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
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and 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 nn nn nn nn nn nn nn nn nn nn
the 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.
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The current process being executed is suspended and the current values of the
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registers are pushed to the system stack
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2. The appropriate Interrupt Service Routine is found and called to handle the
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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
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the 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
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Service 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
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interrupt is received? - correct answer-To save the volatile environment as the
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registers are 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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instructions by fetching, decoding and executing instructions in the fetch-decode-
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execute cycle nn
Computer Organisation And n n n
Architecture Exam With All Answers
n nn n n n
Correct n
What are the steps in the fetch part of the fetch-decode execute cycle (in words)? -
nn nn nn nn nn nn nn nn nn nn nn nn nn nn nn nn
correct answer-1. The contents of the Program Counter are copied onto the MAR
nn nn nn nn nn nn nn nn nn nn nn nn nn
2. The contents of the MAR are transferred to the memory through the address bus
nn nn nn nn nn nn nn nn nn nn nn nn nn nn
where it receives a control signal from the control unit indicating a memory read
nn nn nn nn nn nn nn nn nn nn nn nn nn nn
3. The contents of the memory at the received address are transferred to the MBR
nn nn nn nn nn nn nn nn nn nn nn nn nn nn
through the data bus
nn nn nn nn
At the same time, the PC is incremented by 1
nn nn nn nn nn nn nn nn nn
4. The contents of the MBR are copied onto the CIR
nn nn nn nn nn nn nn nn nn nn
What are the steps in the fetch part of the fetch-decode execute cycle (in register
nn nn nn nn nn nn nn nn nn nn nn nn nn nn
transfer notation)? - correct answer-1. MAR ← [PC]
nn nn nn nn nn nn nn nn nn
2. MBR ← [Memory]addressed
nn nn nn
PC ← [PC] + 1
nn nn nn nn
3. CIR ← [MBR]
nn nn nn
, What are the steps in the decode and execute parts of the fetch-decode execute
nn nn nn nn nn nn nn nn nn nn nn nn nn
cycle? - correct answer-1. Control unit splits the instruction in the CIR into opcode
nn nn nn nn nn nn nn nn nn nn nn nn nn nn nn
and operand
nn nn nn
2. Control unit uses opcode to identify the instruction being executed and the part of
nn nn nn nn nn nn nn nn nn nn nn nn nn nn
the processor executing the instruction
nn nn nn nn nn
3. Control unit generates necessary control signals for execution
nn nn nn nn nn nn nn nn nn
4. Certain actions are performed depending on the instruction
nn nn nn nn nn nn nn nn
What are the possible actions the processor can take in the execute part of the fetch-
nn nn nn nn nn nn nn nn nn nn nn nn nn nn nn
decode execute cycle? - correct answer--Jump/Branch instruction -> PC is updated
nn nn nn nn nn nn nn nn nn nn nn
-Data is required -> Memory or I/O read is issued
nn nn nn nn nn nn nn nn nn
-Arithmetic/Logic operation -> ALU calculates results and stores in register(s) and nn nn nn nn nn nn nn nn nn nn
the status register updates to show overflow or carry
nn nn nn nn nn nn nn nn nn
What happens in the interrupt part of the fetch-decode execute cycle if an interrupt
nn nn nn nn nn nn nn nn nn nn nn nn nn
signal of higher priority has been received by the processor? - correct answer-1.
nn nn nn nn nn nn nn nn nn nn nn nn nn nn
The current process being executed is suspended and the current values of the
nn nn nn nn nn nn nn nn nn nn nn nn nn
registers are pushed to the system stack
nn nn nn nn nn nn nn
2. The appropriate Interrupt Service Routine is found and called to handle the
nn nn nn nn nn nn nn nn nn nn nn nn
interrupt
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3. After the interrupt has been serviced, the original values of the registers are
nn nn nn nn nn nn nn nn nn nn nn nn nn
retrieved from the stack and execution continues with the instruction addressed by
nn nn nn nn nn nn nn nn nn nn nn nn
the PC
nn nn
What is an interrupt? - correct answer-A signal sent to the processor that suspends
nn nn nn nn nn nn nn nn nn nn nn nn nn nn
execution of the current process until the interrupt is handled with an Interrupt
nn nn nn nn nn nn nn nn nn nn nn nn nn
Service Routine (ISR)
nn nn nn
What sends interrupts? - correct answer-Hardware devices and software programs
nn nn nn nn nn nn nn nn nn nn
Why do the register contents have to be pushed to the system stack when an
nn nn nn nn nn nn nn nn nn nn nn nn nn nn
interrupt is received? - correct answer-To save the volatile environment as the
nn nn nn nn nn nn nn nn nn nn nn nn nn
registers are going to be overwritten so the values would be lost otherwise
nn nn nn nn nn nn nn nn nn nn nn nn nn
What does the use of interrupts allow a processor to do? - correct answer-Multitask
nn nn nn nn nn nn nn nn nn nn nn nn nn nn
(using time slices and timer interrupts)
nn nn nn nn nn nn
What is hardware? - correct answer-The physical components of a computer system
nn nn nn nn nn nn nn nn nn nn nn nn
In brief, what does the processor do? - correct answer-Processes data and
nn nn nn nn nn nn nn nn nn nn nn nn
instructions by fetching, decoding and executing instructions in the fetch-decode-
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execute cycle nn
