care for NW

1. Care for Network & Computer
Hardware

2. Familiarizing with computer hardware
• I/O Units: - External input and output devices, also called
peripherals, connect to the computer’s bus systems through different
types of interfacing circuits.

4. • Input Device
• Input devices are hardware components of a computer that enables the computer to
get data.
• The input units contain all the necessary circuitry to accept data and programs from
peripheral input devices such as keyboards, light mouse, scanner, and so forth, and
convert the information into a form that is usable by the microprocessor.
• The input unit may be used to enter programs and data into the memory unit before
execution, or it may be used to enter data directly to the microprocessor during
execution.

5. • Keyboard: The primary input device for a computer, allowing users to type
information.
• Mouse: Used with graphical interface environments to point to and select
objects on the system's monitor.
• Scanner: Converts printed or photographic information to digital information
that can be used by the computer.
• Microphone: Allows input of voice or music to be converted to digital
information and saved to a file.

6. • Output Device
• The output units contain all the necessary circuitry to transform data from the
computer’s language into a form that is more convenient for the outside world.
Common output devices include video display monitors, speakers, and
printers.
• Monitor: It is the primary output device of computers that visually displays
text and graphics.
• Characteristics of Monitor
• Screen size
• Monitor comes in many different sizes. The size ranges from the small screen built on palmtops and
laptops to extra-large monitors used for special purposes. The standard monitor size for personal
computers is 13 to 17 inches.

7. • Resolution
• The term resolution refers to the degree of detail offered in the presentation of
an image.
• Monitor’s resolution is expressed in pixel per inch.
• Monitor resolution is usually expressed as a × b where a is the number of
horizontal pixels, and b is the number of vertical pixels. For example, 640 × 480
means that the monitor resolution is 640 pixels horizontally by 480 pixels
vertically.
• Resolution is a combination of horizontal pixels, vertical lines, and the refresh
rate.
• A pixel is the smallest image unit the computer is capable of printing or
displaying.
• The standard resolution is: 640 columns X 480 rows of dots

8. • Monitor technology
• CRT: - The CRT (cathode-ray tube) is the main component of a
traditional monitor. The rear of the CRT holds a cylinder that contains one
or more electron guns.
• LCD: - Small notebook and laptop computers use non-CRT displays,
such as Liquid Crystal Display (LCD). They are much lighter and more
compact than CRT monitors and require much less electrical energy to
operate.

9. • Speakers: Reproduce sound. Optional high-quality speakers can be added to
provide improved output from games and multimedia software.
• Printer: Generates a "hard copy" information. Converts digital information
into physical.
• Types of printer:- Printers are generally categorized into impact and non-
impact
• Impact Printers:- In impact printing, the paper and character come
in contact. The most common forms of impact printers were dot-
matrix, Line printers, character printer and daisy-wheel. These create
an impression by striking an inked ribbon with enough force to place
ink on the page. In this, they function very much like typewriters.

10. • Non-impact printers:- Impact printers have been replaced by ink and laser
technology. Here the paper and character has no contact. The characters are
produced on the paper through heat, chemical or spray process. The most
common non-impact printers are: Laser and Ink jet printers.
• Plotter:- Similar to a printer, but uses pens to draw an image. Most often used
with graphics or drawing programs for very large drawings such as charts and
graphs, line drawings, and blue print of buildings.

11. • Input and Output devices
• Some devices handle both input and output functions. These devices are called
input/output (I/O) devices.

12. Device Description
Floppy
disk drive
Mechanism for reading and writing to low-capacity,
removable, magnetic disks. Used to store and easily
transport information.
Hard disk
drive
High-capacity internal (and sometimes external)
magnetic disks for storing data and program files. Also
called fixed disks.
CD
recorder
Also called CD-R. You can copy data to a CD with this
device, but you can only write to a section of the disc
once. Variations on this type of device include compact
disc–rewritable (CD-RW) drives. These drives allow
you to read, write, and overwrite a special CD-ROM-
type disc.
Tape
drive
Large-capacity, magnetic, data storage devices. Ideal
for backup and retrieval of large amounts of data.
Works like a tape recorder and saves information in a
linear format. Unlike magnetic & optical, it uses
sequential data access method.

13. •Secondary storage devices
• Programs and data disappear from the system’s RAM when the computer is
turned off. Therefore, devices and systems that can be used for long term data
storage are desirable as a second level of memory.
• A number of secondary memory technologies have been developed to extend the
computer’s memory capabilities and store data on a more permanent basis.

14. • Magnetic disk:- In magnetic disk systems, information is stored in
concentric circles around the disk, which are referred to as tracks.
• The tracks on the disk are numbered, beginning with 0, from the outside edge
inward. Because the tracks at the outer edge of the disk are longer than those at
its center, each track is divided into an equal number of equal-sized blocks
called sectors. Each sector holds 512 bytes.
• Heads- The number of heads is relative to the total number of sides of all
the platters used to store data. If a hard disk drive has four platters, it can
have up to eight heads. The maximum number of heads is limited by BIOS
to 16.

15. • Cylinders:- Data is stored in circular paths on the surface of each platter.
Each path is called a track. There are hundreds of tracks on the surface of
each platter. A set of tracks is called a cylinder.

16. • Sectors per Track:- A hard disk drive is cut (figuratively) into tens of
thousands of small arcs, like a pie. Each arc is called a sector and holds
512 bytes of data. The important value is the number of sectors per track.

17. • How data stored & accessed in magnetic disk
• Data is stored and accessed randomly. In data access time, there are three
conditions Seek, Rotational delay/Latency and Data Transfer.
• As soon as a disk unit receives the read/write command, the read and write
commands are positioned on the specific track. The time take in doing so is
known as Seek Time.
• Once the heads are positioned on the desired track, the disk is rotated
constantly and the head has to wait for the required sector (data), this delay is
known as Rotational Delay Time/Latency. The rate at which the data is read
from or written to disk is known as Data Transfer Rate.
• The combination of seek, latency and data transfer time is called Access
Time. It refers to the time it takes to transfer Character (information) from
memory to/from the processor.

18. • Types of magnetic disk
• Floppy
• Hard Disk

19. • Optical disk
• In optical disk data is stored in a single long track which is suitable for
recording large blocks of sequential data such as movies, music etc.
• Types:-
• CD-ROM (Compact Disk Read Only Memory):- there are called as ROM
because these disks are not used to store information easily like magnetic
disk and tape. Are of two types,
• CD-R:- Once data is stored, can’t be erased or rewritten.
• CD-RW:- Data can be stored, erased and rewritten.
• DVD(Digital video Disk):- are the same with CDs, the main difference is
storage capacity. CD stores up to 700 MB and DVD stores up to 17 GB.
DVD has large storage capacity than CD

20. • Magnetic tape:- In magnetic tape systems, data is stored in sequential
tracks along the length of the tape.
• Each track is divided into equal-sized blocks.
• The blocks are separated by small gaps of unrecorded space. Multiple tracks
can be recorded across the width of the tape.
• Using multiple read/write heads, the tracks can be read simultaneously as the
tape moves forward. Is mostly used to take back up, because of its slower
speed

21. •Maintenance
• The primary goal of maintenance is to avoid or mitigate the consequences of
failure of equipment.
• This may be by preventing the failure before it actually occurs which Planned
Maintenance and Condition Based Maintenance help to achieve.
• It is designed to preserve and restore equipment reliability by replacing worn
components before they actually fail.
• Preventive maintenance activities include partial or complete service at
specified periods, In addition, workers can record equipment deterioration so
they know to replace or repair worn parts before they cause system failure.
• The ideal preventive maintenance program would prevent all equipment failure
before it occurs.

22. • Maintenance vs. Repair:
• Repairs are services that are required /necessary when something on your
machine is not working properly.
• Maintenance is the routinely scheduled services, inspections, replacements of
parts that the manufacturer recommends based on the age of your machine and
varies from machine to machine and what kind of work is done with it. You will
find the schedule for your

23. •Need for Maintenance
• Information Technology (IT) maintenance is needed to ensure that the deployed IT
continues to meet or satisfy user requirements.
• Maintenance is applicable to software developed using any IT regardless of the life
cycle model (e.g., waterfall) used for its development. IT is subject to changes for
corrective and non-corrective software actions. Some maintenance actions are
performed to:
 Correct faults
 Improve the design
 Implement enhancements
 Interface with other systems
 Adapt programs so that different hardware, software, system features, and telecommunications
facilities can be used
 Migrate legacy software
 Retire software

24. The maintainer's activities are comprised of several characteristics:
 Maintaining control over the software's day-to-day functions
 Maintaining control over software modification (baselines)
 Perfecting existing functions (change management)
 Preventing IT performance and security from degrading to unacceptable levels

25. •Types of maintenance
A.Preventive maintenance: Preventive maintenance (PM) has the
following meanings:
1.The care and servicing by personnel for the purpose of maintaining
equipment and facilities in satisfactory operating condition by
providing for systematic inspection, detection, and correction of
incipient failures either before they occur or before they develop into
major defects.
2.Maintenance, including tests, measurements, adjustments, and parts
replacement, performed specifically to prevent faults from occurring.

26. • Preventive maintenance can be described as maintenance of equipment or
systems before fault occurs. It can be divided into two subgroups:
 planned maintenance and
 Condition-based maintenance.
• The main difference of subgroups is determination of maintenance time, or
determination of moment when maintenance should be performed.
• Condition-based maintenance
• Condition based maintenance shortly described is maintenance when need
arises.
• This maintenance is performed after one or more indicators show that
equipment is going to fail or that equipment performance is deteriorating.

27. • CBM has some advantages over planned maintenance:
 Improved system reliability
 Decreased maintenance costs
 Decreased number of maintenance operations causes decreasing of human error
influence
• Disadvantages are:
 High installation costs, for minor equipment items more than value of equipment
 Unpredictable maintenance periods are causing costs to be divided unequally
 Increased number of parts (CBM installation) that need maintenance and checking

28. B. Predictive maintenance
• Predictive maintenance (PdM) techniques help determine the condition of in-
service equipment in order to predict when maintenance should be performed.
• This approach offers cost savings over routine or time-based preventive
maintenance, because tasks are performed only when warranted.
• PdM, or condition-based maintenance, attempts to evaluate the condition of
equipment by performing periodic or continuous (online) equipment condition
monitoring.
• The ultimate goal of PdM is to perform maintenance at a scheduled point in time
when the maintenance activity is most cost-effective and before the equipment loses
performance within a threshold.
• This is in contrast to time- and/or operation count-based maintenance, where a piece
of equipment gets maintained whether it needs it or not. Time-based maintenance is
labor intensive, ineffective in identifying problems that develop between scheduled
inspections, and is not cost-effective.

29. C. Break down (Corrective) maintenance can be defined as the
maintenance which is required when an item has failed or worn out, to bring it
back to working order.
• Corrective maintenance is the most commonly used maintenance approach, but
it is easy to see its limitations.
• When equipment fails, it often leads to downtime in production, and sometimes
damages other parts.
• In most cases, this is expensive. Also, if the equipment needs to be replaced, the
cost of replacing it alone can be considerable.
• Reliability of systems maintained by this type of maintenance is unknown and
can not be measured. Therefore, corrective maintenance is carried out on all items
where the consequences of failure or wearing out are not significant (less
important items) and the cost of this maintenance is not greater than preventive
maintenance.

30. • To make it simple:
 Preventive maintenance is conducted to keep equipment working and/or extend
the life of the equipment.
 Corrective maintenance, sometimes called "repair", is conducted to get
equipment working again.
D. Improvement maintenance: maintenance is performed to improve
(upgrade) the machine.
• This means, make the machine more functional than the previous in different
aspects by replacing some parts of the machine with higher capacity.

31. • Maintenance work Order
 A work order is an order received by an organization from a customer or
client, or an order created internally within the organization. A work order may
be for products or services.
 A job order is a written document which contains orders to perform a job. Job
orders are also known as work orders.
• Job order (work order) will probably state:
1.the Nature of problem
2.the Cause of problem
3.the Action code
4.the Work order steps

32. •Implement maintenance procedure
•Implementing maintenance procedure include the
following steps
1.Identify Equipment and software to be maintained
2.Identify Resource for maintenance
 Identify type of materials(parts)required ,
 identify tools required during the process
3.identify best practice and document Including, precautions to
be considered during the process

33. Safety precaution
• Electrostatic Discharge (ESD)
 is the sudden and momentary electric current that flows between two
objects at different electrical potentials caused by direct contact or induced
by an electrostatic field.
o Is a Rapid transfer of electrostatic charge between two objects, usually
resulting when two objects at different potentials come into direct contact
with each other. ESD can also occur when a high electrostatic field
develops between two objects in close proximity.

34.  The term is usually used in the electronics and other industries to
describe momentary unwanted currents that may cause damage to
electronic equipment.
 ESD is a serious issue in solid state electronics, such as integrated
circuits. Integrated circuits are made from semiconductor materials
such as silicon and insulating materials such as silicon dioxide.
Either of these materials can suffer permanent damage when
subjected to high voltages; as a result there are now a number of
antistatic devices that help prevent static build up.
• Note:ESD is one of the major causes of device failures in the
semiconductor industry.

35. Avoiding ESD
• The best method of preventing ESD is to use an ESD wrist strap and/or use a
grounding mat or table. However, because most users do not have access to such
items, we have included the below steps to help reduce the chances of ESD as much
as possible.
• Zero Potential - Most importantly, make sure you and the computer are at Zero
Potential by continuously touching an un-painted metal surface of the chassis or the
computer power supply case.
• Standing - It is also very important that you are standing at all times when working
on the computer. Setting on a chair can generate more electrostatic.
• Cords - Make sure everything is removed from the back of the computer (power cord,
mouse, keyboard, etc).
• Clothes - Make sure not to wear any clothing that conducts a lot of Electrical Charge,
such as a wool sweater.
• Weather - Electrical storms can increase the ESD risk; unless absolutely necessary,
try not to work on a computer during an electrical storm.
• Accessories - To help reduce ESD and help prevent other problem, it is also a good
idea to remove all jewelry.

36. Using wrist strap
• Also known as an antistatic strap or antistatic wrist strap, a wrist strap is a
strap that wraps around the users wrist like a bracelet and has a cord or other
connection coming from that bracelet that attaches to the device being worked
on, clips onto, or plugs into.
• The wrist strap keeps the user grounded, which helps prevent electrostatic
damage to the device being worked on.
• While working on a computer you could place your wrist in the strap and attach
the other end to a metal portion of the computer case.

37. Touching the metal case or power supply
• Make yourself and the computer at Zero Potential by continuously
touching an un-painted metal surface of the chassis or the computer
power supply case.
• Assuming that your PC is grounded, you can ground yourself by just
keeping one hand in contact with the bare metal frame (not a painted or
coated surface) of the computer case.
• Keep the PC power cord plugged in to a (3-prong) grounded outlet and
turn off the rocker switch on the back of the power supply. If the power
supply does not have a switch on the back, this won't work, however.
• Note: Never work on a PC with the power on. In that case, you should
buy an anti-static band or try another method of grounding.

38. Bootable disk
 A boot disk is a removable digital data storage medium from which a computer
can load and run (boot) an operating system or utility program. The computer
must have a built-in program which will load and execute a program from a
boot disk meeting certain standards.
 A boot disk will allow you to boot off of a diskette instead of your hard drive.
This diskette can be used to fix issues that may arise during the lifetime of your
computer and/or to help load older MS-DOS games. Keep in mind this diskette
is completely different than a Restore CD or Disc that may have been included
with your computer.

39. •Boot disks are used for:
 Operating system installation.
 Data recovery
 Data purging
 Hardware or software troubleshooting.
 Customizing an operating environment.
 Software demonstration.
 Administrative access in case of lost password is possible with an
appropriate boot disk with some operating systems.
 Games (e.g. for Amiga home computers)

40. • Rescue disk
• A disk that can be used to start up a computer when the hard drive fails to
boot. Also called emergency startup disk (ESD) or startup disk.
• Diagnosis Software
• A diagnostic program is a program written for the express purpose of locating
problems with the software, hardware, or any combination thereof in a system, or a
network of systems. Preferably, diagnostic programs provide solutions to the user
to solve issues.
• POST diagnostic card
• (Power On Self-Test card) A diagnostic board that is plugged into a PC's
peripheral bus in order to display the BIOS's POST codes on a built-in readout.
• The last POST code displayed before the system locks up identifies the problem
area. POST codes are different for each BIOS vendor (of course).

41.  A POST card is a small diagnostic tool that displays error codes generated
during the Power On Self-Test.
 These errors, called POST codes, correspond directly to a test that has failed
and can help determine what piece of hardware is causing an issue.
 Most POST cards plug directly into expansion slots in the motherboard while a
few others connect extern POST card

42. • Utility software
• Utility software is a kind of system software designed to help analyze,
configure, optimize and maintain the computer. A single piece of utility software
is usually called a utility (abbr. util) or tool.
• Utility software should be contrasted with application software, which allows
users to do things like creating text documents, playing games, listening to music
or surfing the web. Rather than providing these kinds of user-oriented or output-
oriented functionality, utility software usually focuses on how the computer
infrastructure (including the computer hardware, operating system, application
software and data storage) operates.
• Most utilities are highly specialized and designed to perform only a single task
or a small range of tasks. However, there are also some utility suites that combine
several features in one piece of software.

43. • Most major operating systems come with several pre-installed utilities.
• Utility software categories
 Disk storage utilities
 Disk defragmenters can detect computer files whose contents are broken across several
locations on the hard disk, and move the fragments to one location to increase efficiency.
 Disk checkers can scan the contents of a hard disk to find files or areas that are corrupted in
some way, or were not correctly saved, and eliminate them for a more efficiently operating
hard drive.
 Disk cleaners can find files that are unnecessary to computer operation, or take up
considerable amounts of space. Disk cleaner helps the user to decide what to delete when
their hard disk is full.
 Disk space analyzers for the visualization of disk space usage by getting the size for each
folder (including sub folders) & files in folder or drive. showing the distribution of the used
space.
 Disk partitions can divide an individual drive into multiple logical drives, each with its own
file system which can be mounted by the operating system and treated as an individual drive.

44.  Backup utilities can make a copy of all information stored on a disk, and
restore either the entire disk (e.g. in an event of disk failure) or selected files
(e.g. in an event of accidental deletion).
 Disk compression utilities can transparently compress/uncompress the contents
of a disk, increasing the capacity of the disk.
 File managers provide a convenient method of performing routine data
management tasks, such as deleting, renaming, cataloging, uncataloging,
moving, copying, merging, generating and modifying data sets.
 Archive utilities output a stream or a single file when provided with a directory
or a set of files. Archive utilities, unlike archive suites, usually do not include
compression or encryption capabilities. Some archive utilities may even have a
separate un-archive utility for the reverse operation.
 System profilers provide detailed information about the software installed and
hardware attached to the computer.

45.  Anti-virus utilities scan for computer viruses.
 Hex editors directly modify the text or data of a file. These files could be data or an
actual program.
 Data compression utilities output a shorter stream or a smaller file when provided
with a stream or file.
 Cryptographic utilities encrypt and decrypt streams and files.
 Launcher applications provide a convenient access point for application software.
 Registry cleaners clean and optimize the Windows registry by removing old registry
keys that are no longer in use.
 Network utilities analyze the computer's network connectivity, configure network
settings, check data transfer or log events.
 Command line interface (CLI) and Graphical user interface (GUI) Allows the
user to contact and make changes to the operating system.

46. Preventive maintenance
• To prolong the life of your PC, you simply must inspect and clean it regularly.
• Cleaning your PC on a regular basis can prevent overheating and ESD. During
the inspection process, look for damaged or cracked components, improperly
seated components, frayed cables, and loose connections.
• Note: ESD Electrostatic discharge is a quick electrical charge that occurs when
two objects with different electrical potentials come into contact with each other.
More on this subject in

47. Cleaning the system unit, mouse, Keyboard, Monitor
• Using Liquid Cleaning Compounds
• Before using any liquid cleaning compound make sure that your computer is
turned off.
• If the PC has power when you use liquid cleaners, you run the risk of damaging
or shorting out your components, which is an expensive risk to take.
• Also make sure that the component you have cleaned with a liquid cleaner is
thoroughly dry before turning your computer back on!

48. • Clean or Soapy Water and a Damp Cloth
• In some cases, you need only a bit of water and a damp cloth for cleaning
chores, such as when cleaning the mouse ball, the outside of the mouse, or the
exterior of the monitor or computer case.
• If water alone cannot do the job thoroughly, you can use mild soapy water on
your damp cloth. Make sure that the cloth is damp and not wet and that you do
not splash or drip water into your components.
• If the keys on your keyboard start to stick or you have spilled a cup of coffee
into your keyboard, or, for that matter, you just know that there is a lot of dirt
under the keys, you can clean the keyboard with distilled water.
• Some will use a light silicone spray lubricant, but water does nearly as good a
job.
• Keep in mind that if you want your keyboard to work again, you need to make
sure that it is unplugged before you clean it and that it is thoroughly dry before
you plug it in again. As a general rule, wait at least 48 hours before re-attaching
the keyboard to your system.

49. • Denatured Alcohol
• The best thing to use for cleaning floppy drive heads is denatured
alcohol. But how do you get it in there? You can't just pour it in! You
need to use a lint free swab dipped in the alcohol to clean the floppy
drive heads, or you can purchase a floppy drive cleaning kit, which
almost always comes complete with denatured alcohol.
• Don't clean the mechanical mechanism with alcohol because the parts
are lubricated and the alcohol will dissolve the lubricant.
• When cleaning your mouse, you can use a damp cloth to clean the
cover and ball, as mentioned earlier, but what about the rollers? Some
people pick at the rollers with their fingernails to get all of the dirt off
them, but if you want to keep your fingernails clean you can use a
cotton swab dipped in denatured alcohol to help loosen and remove
the dirt.

50. • Glass Cleaner
• You need to turn your monitor off before cleaning to avoid damage to the
screen.
• Many technicians clean the monitor screen with regular glass cleaner. Under
most circumstances, however, water and a damp cloth will do the job just fine.
Water is the safest cleaning liquid you can use on a monitor.
• When cleaning the LCD display screen of a laptop, do not use glass cleaner at
all. You will melt the screen!
• Fabric Softener
• Some technicians like to use a mixture of 1 part fabric softener to 10 parts water
to clean the plastic casing of their computer components. As a cleaning solution
it's not as good as mild soap and water, but as an anti-static solution it's
excellent! Use it after the cleaning process to help protect your computer from
the harmful effects of static electricity.

51. • Cleaning Contacts and Connectors
• To protect your contacts and connectors from becoming dirty, avoid
touching them with your hands. Your skin contains natural oils that
can leave a residue on contacts and connectors, and that residue needs
to be cleaned off. Leaving the contacts untouched will reduce the
amount of residue and make them easier for you to clean.
• Denatured Alcohol
• You should regularly inspect your contacts and clean them with
denatured alcohol.
• Denatured alcohol is the best solution for cleaning the oily residue
caused by human oil secretions, and it evaporates, leaving no residue
behind.

52. • Erasers
• Some technicians use an eraser to rub residue off contacts, but this leaves a residue
of its own and may actually rub the contacts right off.
• If you absolutely must use erasers, make sure you use the white ones, and
immediately clean any rubber residue off of the contacts.
• Never, ever use pink erasers to clean contacts as these contain acids that have the
potential to destroy your contacts.
• Non-Static Vacuums
• Common household dust kills PCs.
• Throw in some dog and cat hair and you might as well call a priest right now.
• A dust buildup can cause dreaded static and can cause your components to
overheat and become useless.
• When removing dust buildup from your keyboard, inside your computer's case,
and from your components, use a non-static vacuum Many hand-held vacuums are

53. • A non-static vacuum
• Note that you should definitely not use a common household vacuum cleaner.
These create static electricity and can damage your PC!
• Compressed Air
• Compressed air works well for getting the dust out of power supply fans,
expansion slots, and keyboards, but you need to exercise care in using it for
blowing the dust off components and the inside of the case.
• It is not uncommon to blow the dust off one component right onto another
component.
• You also need to exercise extreme care when using compressed air, because the
liquid that compresses the air sits in the bottom of the can and is usually not
released unless you turn the can upside down or sideways. This liquid can
damage or destroy your components.

54. • Lint-Free Cloths
• Lint-free cloths are excellent for removing dust from your computer. The cloths
used for cleaning eyeglasses work the best, because they will not scratch
surfaces or leave lint behind.
• Make sure you never use "dry dusting" lint-free cloths and the like for cleaning
anything in or on your computer. Cloths such as the Swiffer Sweeper do
wonders for dusting those hard-to-reach places in your house, but they use static
electricity to collect the dust.

55. Component protection and storage
Electrical problems
• You need to protect your computing environment from any kind of power
surge, or power sags, as either of these events can cause severe damage to your
system.
• Many things outside the control of normal folks cause sags and surges, such as
electrical brownouts and blackouts, spikes on the electrical grid, lightning, and
electromagnetic interference.
• Brownouts
• Power sags are usually caused by brownouts, where your lights may flicker or
grow dimmer.
• In other words, a power sag occurs when the supply of electricity drops
dramatically but does not go out completely. When the power or electricity
returns to its original level, your computer cannot handle the quick and drastic
change and damage may occur.

56. • Blackouts
• Power surges are caused when the power or electricity goes out completely and
comes back on suddenly. In the event of a power surge, any files that you have
not saved will most likely become corrupted or lost forever.
• Power surge
• Power surges occur when something boosts the electrical charge at some point
in the power lines. This causes an increase in the electrical potential energy,
which can increase the current flowing to your wall outlet. A number of
different things can cause this to happen.
• The most familiar source is probably lightning, though it's actually one of the
least common causes. When lightning strikes near a power line, whether it's
underground, in a building or running along poles, the electrical energy can
boost electrical pressure by millions of volts.
• This causes an extremely large power surge that will overpower almost any
surge protector. In a lightning storm, you should never rely on your surge
protector to save your computer. The best protection is to unplug your
computer.

57. • A more common cause of power surges is the operation of high-power
electrical devices, such as elevators, air conditioners and refrigerators. These
high-powered pieces of equipment require a lot of energy to switch on and turn
off components like compressors and motors.
• EMI
• EMI, or electromagnetic interference, is caused not by storms, but by noise
created by high voltage between two cables or excessively long cables.
• When EMI occurs, your PC may experience sags and surges in the amount of
electricity that is provided to it. The threat of EMI can be combated through the
use of cables with a Mylar coating and through a noise filter, which will control
the amount of electricity that reaches your PC and remove the EMI. Noise filters
can be purchased as stand-alone products or can be incorporated into an
uninterruptible power supply (more on those in the next section).

58. System Protection devices
• Saving Your PC from Electrical Problems
• Any kind of power failure, sag, surge, or spike can cause irreversible damage to
your PC and its components. So you simply must protect your PC from these
events! Fortunately, many products on the market can help you prevent these
events from damaging your PC. These products are called uninterruptible power
supplies (UPS) and surge suppressors.
• Uninterruptible Power Supplies (UPS)
• A UPS helps in blackout situations, during which the electricity cuts off
completely for a period of time, and brownouts, during which the electrical
supply sags well below the level needed to run your PC.
• Every UPS has batteries that provide backup power, thus enabling you to save
your work and shut down your PC properly.
• A UPS is thus sometimes called a battery backup.

59. • Note that a UPS does not provide unlimited Power so you can keep working while the
city lights are out. What it does provide you is a short window of a couple of minutes
to save and shut down.
• UPSs come in two main varieties, standby power systems (SPS) and online UPS.
Both of these will protect your system in the event of a power outage or sag, but they
work differently and provide different levels of protection.

60. • Stabilizer
 a device for making something stable
 an electronic device for producing a direct current supply of constant voltage