Processor Structure & Function

Question 1

What are the components that make up the CPU?

Answer 1

• Control Unit
• Busses
• Arithmetic Logic Unit
• Dedicated Registers

Question 2

What is the control unit?

Answer 2

The part of the processor that co-ordinates the activity of all other components

Question 3

What does the control unit do?

Answer 3

• Controls and co-ordinates the activities of the CPU.
• Directing the flow of data between the CPU and other devices
• Accepts the next instruction, decodes it into several steps, manages its execution and stores the resulting data back in memory or registers.

Question 4

What is a bus?

Answer 4

A series of connectors that transfer signals between internal components.

Question 5

What is the system bus?

Answer 5

The system bus consists of three separate busses, carrying control signals, addresses and data.

Question 6

What are the three signal busses?

Answer 6

• Control bus
• Data Bus
• Address Bus

Question 7

What bus are control signals sent along?

Answer 7

Control bus, between the control unit and the other components of the computer.

Question 8

What are the various control signals?

Answer 8

• Memory Read
• Memory Write
• Bus request
• Bus grant
• Clock

Question 9

What does memory read do?

Answer 9

Causes data from the addressed location in RAM to be placed on the data bus.

Question 10

What does memory write do?

Answer 10

Causes data on the data bus to be written into the addressed location in RAM

Question 11

What does bus request do?

Answer 11

Indicates that a device is requesting use of the data bus

Question 12

What does bus grant do?

Answer 12

Indicates that the CPU has granted access to the data bus

Question 13

What does clock do?

Answer 13

Used to synchronise operations.

Question 14

What does interrupt request do?

Answer 14

Indicates that a device is requesting access to the CPU.

Question 15

What is a unique feature of the control bus?

Answer 15

• The control bus is a bi-directional bus.

* Signals can be carried in both directions.

Question 16

What is the purpose of the control bus?

Answer 16

Transmit command, timing and specific status information between system components.

Question 17

What is the purpose of the data bus?

Answer 17

Provides a bi-directional path for moving data and instructions between system components.

Question 18

What is a word?

Answer 18

• Memory is divided up internally into units known as words.
• A word is a fixed size group of digits, usually 16,32 or 64 bits, which is handled as a unit by the processor, different processors have different word sizes.

Question 19

What is the purpose of the address bus?

Answer 19

Address bus transmits the memory addresses of words that are used as operands in program instructions, so data can be retrieved and sent back to the processor.

Question 20

What is the purpose of the ALU?

Answer 20

• Performs arithmetic, logical and shift operations on data.

Question 21

What are some examples of arithmetic operations?

Answer 21

• Add
• Subtract
• Multiply
• Divide

Question 22

What are some examples of logical operations?

Answer 22

• AND
• OR
• NOT
• XOR

Question 23

What are some examples are shift operations?

Answer 23

Move bits to the left or right within a register

Question 24

What are registers?

Answer 24

Special memory cells that operate at very high speed.

Question 25

What is the register for the ALU?

Answer 25

Accumulator

Question 26

Where does the ALU store it’s data?

Answer 26

Accumulator

Question 27

What are the the various other dedicated registers?

Answer 27

• Program Counter
• Current instruction register
• Memory address register
• Memory data register

Question 28

What is the purpose of the program counter?

Answer 28

Holds the address of the next instruction to be executed. instruction is copied from the current instruction register.

Question 29

What is the purpose of the current instruction register?

Answer 29

Holds the current instruction being executed, which is split into opcode and operand.

Question 30

What is the purpose of the memory address register?

Answer 30

Holds the address in memory where the processor is required to fetch, or to where data is written.

Question 31

What is the purpose of the memory data register?

Answer 31

Used to temporarily store data read from or written to memory, sometimes known as the memory buffer register.

Question 32

What ist he purpose of the accumulator?

Answer 32

Hold immediate results of an instruction.

Question 33

What is the purpose of the processor?

Answer 33

Carry out instructions from programs stored in memory.

Question 34

What is the fetch decode execute cycle?

Answer 34

The sequence of operations involved in executing an instruction.

Question 35

What are the stages of the fetch stage?

Answer 35

• Address of the next instruction is copied from the PC to the MAR.
• Instruction held at the address is copied to the MDR
• Contents of the PC are incremented
• Contents of the MDR are copied to the CIR ( Current Instruction Register ).

Question 36

What are the stages of the decode stage?

Answer 36

• Instruction held in the CIR is decoded.
• It is then split into operand and opcode to determine the type of instruction it i, additional data if required is fetched from memory.
• It is then passed onto the accumulator.
• Instruction now in the CIR, the control unit can work out what needs to be done to carry it out.

Question 37

What are the stages of the execute stage?

Answer 37

• Instruction is executed and the result is held in accumulator or stored in memory.

Question 38

What is the opcode?

Answer 38

Opcode is used to determine the type of instruction and what hardware to use to execute it, the operation that is to be carried out.

Question 39

What does the operand hold?

Answer 39

• Address of the data to be used with the operation, which is then copied to the MAR.
• The actual data to be operated on, which will be copied to the MDR.