The processor

Question 1

Explain the role of a processor

Answer 1

The processor or central processing unit is the internal hardware component of the computer that is responsible for processing data and executing the instructions of programs.

Question 2

Explain the role of the ALU

Answer 2

It is responsible for performing arithmetic calculations and logical operations.

Question 3

Explain the role of the control unit

Answer 3

The control unit is in charge of organising the sequence in which program instructions are executed, followed by decoding the instructions.

Question 4

Explain the role of the clock

Answer 4

The system clock generates regular clock pulses by emitting a signal that continuously oscillates between a low (0) and a high (1) state.

Question 5

Explain the role of general purpose registers

Answer 5

They keep the results of the intermediate calculations that are produced as part of a larger computation.

Question 6

Explain the role of the program counter

Answer 6

Holds the address of the next instruction to be executed by the processor.

Question 7

Explain the role of the current instruction register

Answer 7

Holds the current instruction that the processor is executing.

Question 8

Explain the role of the memory address register

Answer 8

Temporarily holds the address of the memory location (in main memory) that the processor needs to access, either to read from or write to.

Question 9

Explain the role of the memory buffer register

Answer 9

Temporarily holds the data values or instructions that are read from or written to the main memory.

Question 10

Explain the role of the status register

Answer 10

Used to store information about the result of the last instruction that the ALU executed.

Question 11

Explain the role of the accumulator

Answer 11

Stores the result of any calculation processed by the ALU.

Question 12

What is an instruction set?

Answer 12

the complete set of all the instructions in machine code that can be recognized and executed by a CPU.

Question 13

What can instructions consist of?

Answer 13

instructions consist of an opcode and
one or more operands (value, memory address
or register).

Question 14

What happens in an immediate addressing mode?

Answer 14

The operand is treated as data.

Question 15

What happens in a direct addressing mode?

Answer 15

the operand is treated as a memory address where data is stored.

Question 16

What is an interrupt?

Answer 16

An interrupt is a signal that is sent to the processor to request immediate attention.

Question 17

What happens when the processor is interrupted?

Answer 17

When the processor receives an interrupt request, it suspends what it is doing and runs the process associated with the interrupt.

Question 18

What is an ISR?

Answer 18

An ISR (interrupt service routine) is a mini program that has been designed to respond to an interrupt’s request.

Question 19

What are the steps of servicing an interrupt?

Answer 19

1) The processor receives the interrupt
2) The processor completes the fetch-decode-execute cycle of the instruction that it was running when it received the interrupt
3) The current contents of the processor registers (including the program counter) are saved to memory
4) The origin of the interrupt is identified so that the appropriate ISR is called
5) All other lower-priority interrupts are put on hold to allow the ISR to finish running
6) The program counter is updated with the address of the first instruction of the ISR
7) The ISR completes its execution
8) The processor registers are reloaded with the values that were saved to memory
9) The lower-priority interrupts that were put on hold are re-established
10) The program counter is set to point to the address of the next instruction that needs to be executed in the program that the processor was running when it received the interrupt