sem 4

Question 1

what are I/O devices?

Answer 1

I/O devices interact with the computer system and the external environment.

input: camera, mic
output: monitor, projector, screen

They key differences the devices have are the data rate, application, complexity of control unit
of transfer, data representation, and error condition.

Question 2

What are the 3 techniques for performing I/O:

Answer 2

1. Programmed I/O
2. Interrupt-driven I/O
3. Direct Memory Access (DMA)

Question 3

Programmed I/O:

Answer 3

CPU issues an I/O command to an I/O module and process will be busy waiting for operation to be completed.

not efficient, because I/O process needs to be completed before the process can proceed.

(one example is when we are outputting information to printer to print copies)

Question 4

Interrupt-driven I/O:

Answer 4

• employ interrupts
• increase efficiency because CPU does not need to wait for the I/O operation to complete before proceeding.

Question 5

Direct-Memory Access (DMA)

Answer 5

• a DMA module controls the exchange of data between the I/O module and the main memory
  – The CPU sends a request to the DMA module, and the CPU will only be interrupted after the entire block has been
  transferred
  – greatly increases the efficiency (CPU is only involved at the beginning and at the end of the transfer)

Question 6

what are disks?

Answer 6

Disk is one of the most important devices that
computer communicates with

Both traditional disk and Solid-state Disk (SSD) are
widely used in computers

Question 7

transfer time equation

Answer 7

– T = b/rN

T is transfer time,
b is number of bytes to be transferred
N is number of bytes on a track
r is rotational speed (rps)

Question 8

What is RAID

Answer 8

• RAID is an example of fault tolerance.
• RAID uses redundant disk capacity to store parity so
  that it can rebuild the data if there is a disk failure.
• RAID is widely implemented in servers (as hard disks are bound to failure if running long enough)

Question 9

How many RAID levels are there?

Answer 9

7 RAID levels

Question 10

What is RAID Level 0

Answer 10

• have no fault tolerance
• improves the efficiency of the system (performance is much higher)

file is distributed among multiple disks, broken up into multiple pieces, called stripping.

for example, file A can be broken up and located in strip 1, strip 2 and strip 3

Question 11

What is RAID level 1

Answer 11

• mirror
• duplicates two sets of data

helps to ensure we can recover the data if lost.

can recover minimum 1 disk, maximum 4 if the file size if 4 disks. can recover 4 disks if only in the event 4 disks fails.

Question 12

What is RAID Level 4?

Answer 12

• uses one disk to store the parity disks
• allows up to one disk failure

Question 13

What is RAID Level 5

Answer 13

similar to RAID 4 but the parity is striped across all
disks instead of using one whole disk for parity

Question 14

What is RAID Level 6?

Answer 14

uses two different parity calculations, and the parity
is stored across the different disks

allow up to two disks failure

Question 15

What is ZFS File system?

Answer 15

RAID cannot protect against data corruption.

Z File System (ZFS) uses checksum to preserve
integrity of data and files

ZFS also provides volume manager, and it can provide
different RAID levels

ZFS is open-source (supported by many Linux
systems)