Device Management (week 4)

Question 1

I/O systems are designed to handle_______ which are of many magnitudes __________ than the slowest CPU

Answer 1

I/O devices

slower

Question 2

for efficient performance, there should be as much overlap as possible between the
operation of the ___________

Answer 2

I/O devices and the CPU

Question 3

what is device manager

Answer 3

manages the collection of device driveres

Question 4

what does the device manager do

Answer 4

manages the collection fo device drivers

makes it possible for the OS to then provide a standard set of system calls to application programs, which use the devices

Question 5

what do device drivers do ?

Answer 5

A system call might mean different things to different devices. This system call has to be interpreted so that the devices can work. Devices drivers are used to interpret the system calls to ensure that the devices work properly.

Question 6

device driver is the __________ module

Answer 6

device-dependent (comes with equipment you purchased)

Question 7

device manager is the ________ module

Answer 7

device independent

Question 8

what are the 3 categories of devices

Answer 8

block
character
network

Question 9

storage devices are classified into 2 categories called

Answer 9

sequential

direct access

Question 10

what is device status table

Answer 10

device status table is used by the device manager to keep track of the various devices

Question 11

what information does the device status table contain

Answer 11

device id

device status (done, busy, idle)

queue of processing waiting for the device

Question 12

what do programs which perform I/O operations expect

Answer 12

expect the IO operation to be completed before the next statement is executed

Question 13

how can there be a performance gain

Answer 13

we can make the program execute instructions while the IO is taking place

this should be done without violating the serial execution order of the program

Question 14

what is the main problem in trying to integrate many different devices into the computer system

Answer 14

different devices have different characteristics and thus require different methods to access or use.

To use these devices, application programs need to know every device’s characteristics and methods of access. This is not practically possible as new devices are produced all the time

Question 15

How does the OS solve the problem of trying to integrate many different devices into the computer system

Answer 15

OS provides abstraction through its device manager which standardizes the interface required to use all the devices in each class. Application programs just need to know a standard device interface to use all the devices in that class. (FOR EG ALL TYPES OF SCANNERS ETC)

Question 16

how to maximize the IO

Answer 16

to maximize the IO, the CPU can be used to operate on another process when the IO is busy with the original process.

this will increase the efficiency of the computer and reduce the overall time required to execute all the processes

Question 17

what are the 3 techniques used by the OS to optimize the use of devices

Answer 17

–> overlapping processing & IO operations
–> buffering
–> disk optimization

Question 18

how does buffering work

Answer 18

buffering allows the CPU to temporarily store/read data to/from memory when transferring data to/from devices. This allows the device controller to do the actual transfer when the CPU is doing other things,

Question 19

what is the difference between device driver and device controller

Answer 19

device driver is implemented at the software level

device driver is a software program that allows a device to communicate with the operating system

device controller is implemented at the hardware level

device controller is a hardware unit that acts as an interface between the device and the device driver

Question 20

what are the different types of buffering

Answer 20

input buffering
output buffering
hardware buffering
double buffering
circular buffering

Question 21

what is input buffering

Answer 21

copies the data into memory before the process requests it

Question 22

what is output buffering

Answer 22

temporarily stores the data in memory and have it written out to the device when the process resumes execution

Question 23

what is hardware buffering

Answer 23

Implements buffering in the hardware by having specialized registers to act as buffers. This is also known as cache

Question 24

what is double buffering

Answer 24

implement hardware buffering and having a separate buffer implemented at the software level

for eg using primary memory as a buffer

Question 25

what is circular buffering

Answer 25

having a buffer which contains n number of locations. This incresased number of buffers allows for more data to be stored in the buffer

circular buffering is the technique of managing these locations so that they can be reused

Question 26

what are character devices

Answer 26

character based devices (tty/terminal) and serial based devices are where the data is handled one character or byte at a time

Question 27

what are block type devices

Answer 27

block type devices such as hard drives transer data in blocks, typically a multiple of 256 bytes

Question 28

________- and ________ are naming conventions for disk devices

Answer 28

sda, sda1

Question 29

___________ and ________ are naming conventions for terminal devices or virtual consoles

Answer 29

tty0, tty1

Question 30

what are types of randomly accessed memory devices

Answer 30

flash memory
optical drives
rotating magnetic disk
floppy disk

Question 31

what is sequentially accessed storage

Answer 31

magnetic tapes

Question 32

what are the properties of randomly accessed storage devices

Answer 32

–> allows a driver to access blocks of data in the device in any order. Need not be sequential

–> Non-volatile memory (such as USB memory devices) also falls in this category

–> can easily be managed using a common api

Question 33

Although disk based devices are random, we can improve on
their efficiency using _____________________

Answer 33

disk optimization
techniques

Question 34

How can the effectiveness of disk based devices be increased ?

Answer 34

they can be increased in a multiprogramming environment where data blocks
can be read from a large range of locations in
the disk.

Question 35

what is transfer time

Answer 35

Time to copy bits from disk
surface to memory

Question 36

what is Disk latency time

Answer 36

Rotational delay waiting
for proper sector to rotate under R/W head

Question 37

what is Disk seek time

Answer 37

Delay while R/W head
moves to the destination track/cylinder

Question 38

how to calculate Access Time

Answer 38

seek + latency + transfer

Question 39

what are the 4 disk-based optimization techniques?

Answer 39

First-Come-First-Serve (FCFS)

Shortest Seek Time First (SSTF)

SCAN / C-SCAN

LOOK / C-LOOK