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Flashcards in The Processor Deck (20):

What occurs in the fetch stage?

• Processor fetches the program's next instruction from memory.
• Instruction will be stored at a memory address and will contain the instruction in binary code


What occurs in the decode stage?

Processor works out what the binary code at that address means


What occurs in the execute stage?

Processor carries out the instruction.


What is the purpose of the control unit?

• Controls and co-ordinates the activities of the CPU, directing the flow of data between the CPU and other devices.
• Accepts next instruction, breaks down its processing into several sequential steps such as fetching address and data from memory, manages its execution and stores the resulting data back in memory or registers


What is the purpose of the system clock?

Generates a series of signals, synchronising CPU operations.


Where might an accumulator be used?

When there is just a single register in which to store the result of each calculation or logical expression


What are the various dedicated registers?

• Program Counter
• Current instruction register
• SR
• Interrupt Register


What does the PC do?

Holds the address of the next instruction to be executed.


What does the CIR do?

Holds the current instruction being executed


What does the MAR do?

Holds the address of the memory location from which data is to be fetched or which data is to be written


What does the MBR do?

Used to temporarily store the data read from or written to memory.


What does the SR do?

• Contains bits that set or cleared depending on the result of an instruction.
• Keeps track of the status of various parts of the computer.


What is the purpose of the interrupt register?

Stores details of the signals that have been received by the processor from other components attached to it.


What are the four registers that are involved in the fetch execute cycle?

• PC


How are the registers used in the fetch stage?

• Address of the next instruction is copied from PC to the memory address register, address is sent via the address bus to main memory.
• Instruction held at that address is returned along the data bus to the MBR, the PC is also incremented at the same time to hold the address of the next instruction.
• Contents of the MBR are copied to the CIR


How are the registers used in the decode phase?

• Instruction held in the CIR is decoded.
• Instruction is split into opcode and operand and the opcode is used to determine the type of instruction and what hardware to use to execute it.
• Additional data is fetched if necessary and passed to the registers


How are the registers used in the execute phase?

• Instruction is executed, using the ALU if necessary and results are stored in the accumulator, general purpose register or memory.


What factors affect processor performance?

• Number of cores linked together on a single chip
• Amount and type of cache memory
• Clock Speed
• Word length
• Address bus width
• Data bus width


How does clock speed affect processor performance?

• Clock speed is a measure how fast each instruction will be executed, increasing clock speed increases the speed at which the processor executes instructions


How does bus width affect processor performance?

• The width of the bus shows how many bits can be transferred in one pulse of the clock
• Increasing width of the bus means more bits and therefore more data can be passed down it with each pulse of the clock
• Increases how many bits can be transferred simultaneously, meaning more data can be processed within a given time interval.
• Increasing the address bus increases the amount of memory that can be addressed and therefore allows more memory to be installed on the computer