• Structure Of The Processor ( 2 )

Question 1

What are registers?

Answer 1

Special memory cells that operate at very high speed.

Question 2

Where do the calculations of the ALU get stored?

Answer 2

Accumulator stores its data in a register called the accumulator.

Question 3

Why are registers needed?

Answer 3

• 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 4

What are the various dedicated registers?

Answer 4

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

Question 5

What is the purpose of the program counter?

Answer 5

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

Question 6

What is the purpose of the current instruction register?

Answer 6

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

Question 7

What is the purpose of the memory address register?

Answer 7

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

Question 8

What is the purpose of the memory data register?

Answer 8

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

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

Question 9

What is the purpose of the accumulator?

Answer 9

• hold intermediate results of an instruction

Question 10

What is the purpose of the processor?

Answer 10

• Carry out out instructions from programs stored in memory.

Question 11

What are the steps of the fetch decode execute cycle?

Answer 11

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 12

What are the steps of the decode stage?

Answer 12

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 13

What is the execute stage?

Answer 13

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

Question 14

What is the opcode?

Answer 14

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

Question 15

What is the operand?

Answer 15

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 16

What is the purpose of the data bus?

Answer 16

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