Week 5

Question 1

What does the CPU do with I/O devices?

Answer 1

The CPU sends/receives data to/from I/O devices.

Question 2

What are input devices used for?

Answer 2

Set sensitivity, calibrate, switch on/off.

Question 3

What are output devices used for? (examples)

Answer 3

Check readiness, verify success.

Question 4

Where are I/O registers located?

Answer 4

Inside I/O devices, not the CPU.

Question 5

How does the CPU access I/O registers?

Answer 5

Via memory-mapped I/O and port-mapped I/O.

Question 6

What is memory-mapped I/O?

Answer 6

I/O registers mapped to special memory addresses.

Question 7

What are the advantages of memory-mapped I/O?

Answer 7

• Simple; no new CPU instructions needed.

Question 8

What are the disadvantages of memory-mapped I/O?

Answer 8

• Reduces addressable memory
• Risk of accidental access (program bugs).

Question 9

What is port-mapped I/O?

Answer 9

Uses dedicated I/O instructions (e.g., Input, Output).

Question 10

What is the difference between early and modern PC I/O methods?

Answer 10

Early PCs mixed both methods; modern systems prefer memory-mapped I/O.

Question 11

What is the definition of a program?

Answer 11

A sequence of instructions.

Question 12

What is the definition of a process?

Answer 12

A running program.

Question 13

What is the lifespan of a program?

Answer 13

Long (stored until deleted).

Question 14

What is the lifespan of a process?

Answer 14

Limited (ends when execution stops).

Question 15

What is programmed (polling) I/O?

Answer 15

CPU periodically checks I/O device status.

Question 16

What is the main disadvantage of programmed I/O?

Answer 16

CPU constantly busy (inefficient, high power usage).

Question 17

What is interrupt-based I/O?

Answer 17

I/O device notifies CPU when ready (via hardware signal).

Question 18

What happens during an interrupt in the CPU?

Answer 18

CPU pauses current task, runs interrupt handler.

Question 19

What is Direct Memory Access (DMA)?

Answer 19

A dedicated controller handles memory transfers, bypassing CPU.

Question 20

What are the advantages of DMA?

Answer 20

• Frees CPU for other tasks
• Faster bulk transfers.

Question 21

What is an OS’s primary function?

Answer 21

Acts as an interface between hardware, programmers, and users.

Question 22

What is the purpose of the OS kernel?

Answer 22

Core components include process, memory, and I/O management.

Question 23

What does virtualization provide for each process?

Answer 23

Dedicated CPU, contiguous memory, exclusive hardware access.

Question 24

What is the purpose of virtual memory?

Answer 24

Prevents processes from accessing each other’s memory and expands usable memory.

Question 25

What triggers a page fault?

Answer 25

Occurs when a program attempts to access a virtual memory page that is not currently loaded in physical memory

Question 26

What is thrashing in the context of virtual memory?

Answer 26

Overuse of swapping causing slowdowns.

Question 27

What are the states of a process?

Answer 27

* Running * Ready * Blocked.