• Structure Of The Processor ( 1 )

Question 1

What are the various components of the CPU?

Answer 1

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

Question 2

What is the control unit?

Answer 2

• Part of the processor which co-ordinates the activity of all other components.

Question 3

What is the purpose of the control unit?

Answer 3

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

Question 4

What is a bus?

Answer 4

• Series of connectors that transfer signals between internal components.
• Set of parallel wires connecting two or more components of a computer.

Question 5

What is the system bus?

Answer 5

• A set of three separate busses, that carry control signals, addresses and data.
• This is also how the processor is connected to main memory.

Question 6

What are the busses that make up the system bus?

Answer 6

• Control Bus
• Data bus
• Address Bus

Question 7

What is the purpose of the control bus?

Answer 7

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

Question 8

What directional bus is the control bus?

Answer 8

Bi-directional bus, this means signals can be carried in both directions.

Question 9

Why are control lines needed?

Answer 9

• Data and address busses are shared by all components of the system
• Control lines must be provided to ensure that access to and use of the data and address busses by the different components of the system does not lead to conflict

Question 10

What are the various control signals?

Answer 10

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

Question 11

What does memory read do?

Answer 11

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

Question 12

What does memory write do?

Answer 12

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

Question 13

What does bus request do?

Answer 13

Indicates that a device is requesting use of the data bus

Question 14

What does bus grant do?

Answer 14

Indicates that the CPU has granted access to the data bus

Question 15

What does clock do?

Answer 15

Used to synchronise operations

Question 16

What does the arithmetic logic unit do?

Answer 16

Arithmetic logic unit performs arithmetic, logical and shift operations on data

Question 17

What are some examples of arithmetic operations?

Answer 17

• Add
• Subtract
• Multiply
• Divide

Question 18

What are some examples of logical operations carried out by the ALU?

Answer 18

• AND
• OR
• NOT
• XOR

Question 19

What are some examples of shift operations carried out by the ALU?

Answer 19

Moving bits to the left or right within the register.

Question 20

What are registers?

Answer 20

Special memory cells that operate at very high speed.

Question 21

Where do the calculations of the ALU get stored?

Answer 21

Accumulator stores its data in a register called the accumulator.

Question 22

Why are registers needed?

Answer 22

• Main memory is too slow for working data to be stored

* Processor will be then able to immediately access and re use these results in further calculations.

Question 23

What are the various dedicated registers?

Answer 23

• Program Counter
• Current Instruction Register
• Memory address register
• Memory data register

Question 24

What is the purpose of the program counter?

Answer 24

• Holds the memory address of the next instruction to be executed.

Question 25

What is the purpose of the current instruction register?

Answer 25

• Holds the current instruction being executed
• Split into:
- Opcode
- Operand

Question 26

What is the purpose of the memory address register?

Answer 26

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

Question 27

What is the purpose of the memory data register?

Answer 27

• Temporarily store the data read from or written to memory.

* Temporarily holds data moving between the processor and main memory.

Question 28

What is the purpose of the accumulator?

Answer 28

• hold intermediate results of an instruction

Question 29

What is the purpose of the processor?

Answer 29

• Carry out out instructions from programs stored in memory.

Question 30

What are the steps of the fetch decode execute cycle?

Answer 30

1. Address of the next construction is copied from the PC to the Memory Address Register ( MAR )
2. Instruction held at that address is copied to the memory data register
3. Simultaneously, the contents of the program counter ( PC ) are incremented
4. Contents of the MDR are copied to the current instruction register ( CIR ).

Question 31

What are the steps of the decode stage?

Answer 31

5. Instruction is held in the CIR, it is decoded.
6. Split into operand, and opcode to determine the type of instruction, additional data where required is fetched from memory.
7. Passed to the accumulator

Question 32

What is the execute stage?

Answer 32

• Appropriate instruction/opcode is carried out on the operand
• Result held in accumulator or stored in memory.

Question 33

What is the opcode?

Answer 33

Opcode is used to determine the type of instruction, and what hardware to use to execute it.

Question 34

What is the operand?

Answer 34

Holds either:
• Address of the of the data to be used with the operation, which is copied to the MAR.
or
• Actual data to be operated on, which will be copied to the MDR
• The data to be operated on may be passed to the ALU/Accumulator.

Question 35

What is the purpose of the data bus?

Answer 35

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