Input/Output

Question 1

What is an interrupt ?

Answer 1

A hardware signal

Question 2

What is ISR ?

Answer 2

Interrupt service routine

Question 3

When is ISR executed ?

Answer 3

In response to an interrupt

Question 4

Who sends an interrupt to whom ?

Answer 4

I/O device to processor

Question 5

What is the bus control line dedicated to interrupts called ?

Answer 5

Interrupt - Request line

Question 6

What does an interrupt-acknowledge signal do ?

Answer 6

Informs the device that the interrupt signal has been received

Question 7

What is interrupt latency ?

Answer 7

Delay between an interrupt being received and an ISR starts

Question 8

What increases interrupt latency ?

Answer 8

Saving and restoring registers

Question 9

What is the full form of DMA ?

Answer 9

Direct Memory Access

Question 10

What is DMA used for ?

Answer 10

Transfer large blocks of data at high speed

Question 11

What is the advantage of DMA ?

Answer 11

No interference from processor

Question 12

What does DMA do ?

Answer 12

Transfer block of data directly

Question 13

To what does DMA place the block of data in ?

Answer 13

External device and main memory

Question 14

What controls DMA ?

Answer 14

DMA controller

Question 15

What information does the program need to tell the DMA controller before calling it ?

Answer 15

1. Starting address
2. Number of words in block
3. Direction of transfer

Question 16

How does the DMA controller inform the processor that the instruction has been executed ?

Answer 16

It sends an interrupt signal

Question 17

Can the program that requested DMA transfer continue while DMA executes ?

Answer 17

No, it can’t

Question 18

Can the processor do any other work ?

Answer 18

Yes, it can execute other programs

Question 19

In an OS, what kind of programs request I/O operations ?

Answer 19

Application programs

Question 20

What does the OS do when a DMA operation starts to the application program that requested it ?

Answer 20

It puts the application in blocked state

Question 21

When does the application program go back to the runnable state ?

Answer 21

After the DMA controller sends an interrupt request indicating it’s end

Question 22

What is a bus master ?

Answer 22

Device that can initiate data transfers on a bus at any given time

Question 23

What are the two main approaches to bus arbitration ?

Answer 23

Centralised and distributed

Question 24

What happens in centralised bus arbitration ?

Answer 24

Single bus arbiter performs arbitration

Question 25

What happens in distributed bus arbitration ?

Answer 25

All devices participate in selection of next bus master