Storage and I/O

Question 1

The CPU is attached to main memory via the _______ ____

Answer 1

memory bus

Question 2

Devices are connected to the system via the ___ ____

Answer 2

I/O bus

Question 3

What are buses?

Answer 3

Data paths provided to enable information between CPU(s), RAM, and I/O devices

Question 4

The I/O bus connects a ____ to an ____ device

Answer 4

CPU, I/O

Question 5

What 3 hardware components connect the I/O bus to I/O device?

Answer 5

• I/O ports
• Interfaces
• Device controllers

Question 6

Software interacts with device though device _______

Answer 6

interfaces

Question 7

Device interfaces are just _________ and _______ device registers

Answer 7

programming, reading

Question 8

What 3 values does an interface register have?

Answer 8

• Status
• Command
• Data

Question 9

The status value in an interface register shows the current _______ of the device

Answer 9

status

Question 10

The command value in an interface register tells the device to perform a _____

Answer 10

task

Question 11

The data value in an interface register ______ or ____ data from the device

Answer 11

passes, gets

Question 12

Devices are addressed by direct I/O __________ or _____-______ I/O

Answer 12

instructions, memory-mapped

Question 13

In memory-mapped I/O, a device’s data and command registers are mapped to the _______ ______ _____

Answer 13

processor address space

Question 14

What is the interrupt-driven I/O cycle?

Answer 14

• CPU device driver initiates I/O
• I/O controller initiates I/O
• I/O controller generates interrupt signal with input, output, or error
• CPU receives interrupt and transfers control to interrupt handler
• Interrupt handler processes data and returns
• CPU resumes interrupted task

Question 15

Direct memory access transfers data _____ between I/O device and memory

Answer 15

directly

Question 16

___________ I/O suspends processes until the I/O is complete

Answer 16

blocking

Question 17

Blocking I/O is easy to ___ and ________

Answer 17

use, understand

Question 18

Blocking I/O us ________ and _______ for some needs

Answer 18

inefficient, insufficient

Question 19

__________ I/O return I/O calls as much as possible

Answer 19

nonblocking

Question 20

Nonblocking I/O is implemented via __________

Answer 20

multi-threading

Question 21

_____________ I/O allows processes to run while the I.O executes

Answer 21

asynchronous

Question 22

Asynchronous I/O is _________ to use

Answer 22

difficult

Question 23

The hard disk has been the main form of _____________ storage for decades

Answer 23

persistent

Question 24

The hard disk consists of a large amount of ______

Answer 24

sectors

Question 25

Sectors in a hard disk are in _____-byte blocks

Answer 25

512

Question 26

Hard disks can be viewed as an _____ of sectors

Answer 26

array

Question 27

In hard disks, only single sector accesses are ______

Answer 27

atomic

Question 28

When does a torn write occur?

Answer 28

When a hard disk is accessing multiple sectors at once

Question 29

What is a torn write?

Answer 29

power loss during the multi-sector write, and only some of the sectors were successfully updated

Question 30

In hard disk access, _________ access is faster than _______ access

Answer 30

sequential, random

Question 31

What are four sections of a hard disk?

Answer 31

• Platter
• Track
• Sector
• Cylinder

Question 32

In the hard disk, the _____ moves horizontally from one track to another

Answer 32

head

Question 33

Disk rotate from __ to ____ times/sec

Answer 33

60, 250

Question 34

Explain the process of accessing a block in hard disks

Answer 34

Move the head to desired track (seek time)
•Wait for desired sector to rotate under the head (rotational latency time)
•Transfer the block to a local buffer, then to main memory (transfer time)

Question 35

In hard disks, accesses should minimize ______ _____

Answer 35

seek time

Question 36

Hard disks typically have small ______ (____)

Answer 36

caches, DRAM

Question 37

The DRAM in hard disks hold data _____ from or ________ to the physical disk structure

Answer 37

read, written

Question 38

The DRAM in hard disks allow the device to respond _______ to requests

Answer 38

quickly

Question 39

In the write-back policy, the disk returns ‘completed’ as long as data is in ______

Answer 39

cache

Question 40

Write-back policy as fast, but can be ________

Answer 40

dangerous

Question 41

In the write-through policy, data is guaranteed to reach the ___

Answer 41

disk

Question 42

The write-through policy is safe, but _____

Answer 42

slow

Question 43

What are the 3 objectives of a disk scheduling algorithm?

Answer 43

• Fast disk access time
• High disk bandwidth
• Fairness (maybe)

Question 44

What are 4 disk scheduling algorithms?

Answer 44

• FCFS
• Shortest Scan time first (FCFS)
• C-/SCAN/Elevator
• C-/LOOK

Question 45

The FCFS disk scheduling algorithm processes requests in _____ order

Answer 45

arrival

Question 46

The SSTF disk scheduling algorithm processes requests with the minimum _____ time from current position

Answer 46

seek

Question 47

The main issue of SSTF is ________

Answer 47

starvation

Question 48

In the SCAN/Elevator disk scheduling algorithm, the OS moves across the disk processing requests in order across the ______

Answer 48

tracks

Question 49

What is a sweep in the SCAN algorithm?

Answer 49

A single pass across the disk

Question 50

During SCAN, what happens when a request comes for a block on track that has already been sweeped?

Answer 50

It is queued until the next sweep

Question 51

F-SCAN ______ the queue to be serviced when doing a _______

Answer 51

freezes, sweep

Question 52

F-SCAN avoids _______

Answer 52

starvation

Question 53

C_SCAN sweeps from ______ to ______, then ______ to ______

Answer 53

outer, inner, inner, outer

Question 54

SSTF is _____ and has a natural ______

Answer 54

common, appeal

Question 55

SCAN and C_SCAN perform ________ for systems that place _______ loads on the disk

Answer 55

better, heavy