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In this chapter·
What is computer
·
Generation of computer
·
Classification of computer on the basic of signal
·
Classification of digital computers
·
Common functional Areas of computer system
·
Major part of computer
·
Essential parts of computer
·
How does computer work?
·
Types of memory
·
Some widely used memory devices
·
Input devices
·
Output devices
What is computer:-
Computers is defined in the oxford dictionary
as “ An automatic electronic apparatus for making calculations or controlling
operations that are expressible in numerical or logical terms.
The definitions clearly categoric computer as
electronic apparatus although the first computers were mechanical and electro-mechanical
apparatus. The definition is also pointing towards the two major areas of
computer application viz. data processing and computer assisted
control/operation. The another important confluence of the definition is the
fact that the computer can perform only those operations/ calculations which
can be expressed in logical or numerical terms.
A computer is a device or a programming
electronic machine that perform high-speed mathematical or logical operations
or that assembles, saves, related or processes information .computer does not
have its own mind, that is why have to give it instructions to work. So another
definition of computer can be given as “A computers is a machine that
manipulates data according to a list of instructions. This list of instruction
is recognized as a program. It is only a machine which follows that
instruction, so it is up to the user how to use computer”
In other words “ computers is a programmable
machine that responds to a specific set of instructions in a well- defined manner
and can execute a predefined list of instructions (a program)”. It is an
electronic device, which execute software programs. The computer processes
input through input devices like mouse and keyboard, display output through
output device like color monitor and printer. The size of a computer varies
considerably from very small to very big. The speed of computers also has a
very large. Computers have becomes necessary in today”s world. Millions of
people use computers all over the world. The ability to store and execute lists
of instruction called programs makes computers extremely versatile and
distinguishes then from calculations.
Now we should move ahead and get some knowledge
about how these computers were invented. To fully understand and recognize the
impact computers have on our lives and promises they hold for the future, it is
important to understands their evolution. The developments of computers is
divided into some generations, which makes it easier to understand, are as
follows:
After second world war, governments sought to
develop computers to exploit their potential strategic importance. In 1941 German engineer Konrad zuse developed a computer, the Z3, to design airplanes
and missiles. Howard H. Aiken (1900-1973), a Harvard engineer working with IBM,
succeeded in producing an all electronic calculation by 1944, named as MARK I.
The main function of the computer was to create ballistic charts for the U.s.
navy. Another computer development driven by the war was the electronic
numerical integrator and computer ( ENIAC), produced by a partnership between
the U.S. government and the university of Pennsylvania. ENIAC, unlike the colossus
and mark I, was a general- purpose computer that computed at speeds 1000 times
faster than mark I, In `1951, the UNIVAC I ( universal Automatic computer),
built by Remington rand, became one of the first commercially available
computer.
In first generation computer each computer had
a different binary- coded program called a machine language that told it how to
operate. In this language each and every thing was denoted in 0 & 1 which
made the computer difficult to program and limited its versatility and speed.
Other distinctive features of first generation computers were the use of vacuum
tubes ( responsible for their breath taking size) and magnetic drums for data
storage.
2. Second generations computers( 1956-1963)
The invention of the transistor significantly changed
the computer’s development. The transistor replaced the larges take advantage of transistor
technology were early supercomputers. These machines were costly. However, and
tended to be too powerful for the business sector’s computing needs there by
limiting their attractiveness .
Second generation computers replaced machine
language with assembly language, allowing abbreviated programming codes to
replaces long, difficult binary codes. This made programming more
understandable and easier.
Throughout the early 1960’s’ there were a
number of commercially successful second generations computers used business,
universities, and government from companies such as Burroughs, control data,
Honeywell, IB, Sperry- rand,and others. High level language such as COBOL (
common business oriented language) and FORTRAN( formula translator) come into
common use burring this time.
3. Third generation computers( 1964-1971)
Jack Kilby, an engineer, developed the
integrated circuit (ic) in 1958. The IC combined three electronic compounds
onto a small silicon disc another third generation development included the use
of an operating system that allowed machines to run many different program at
once with a central program that monitored and coordinated the computer’s
memory
During fourth generation, first development was
large scale integration (LSI) that could fit hundreds of components onto one chip. By the 1980s’
very large scale integration (VLSI) compressed hundreds of thousands of
component onto a single chip. Ultra large scale integration ( ULSI) increased
that number up to millions. The intel 4004 chips, development in 1971, took the
integrated circuit one step further by locating all the components of a
computer on a single chips.
In 1981, IBM introduced its personal computer
( pc) for use in the home, office and schools.
As computers became more famous in the workplace, new ways to bind their
potential developed.
As smaller computers became more powerful, they
could be linked together, or networking to share memory space software,
information or data and communicate with each other. As opposed to a mainframe
computer, this was one powerful computer that shared time with many terminal
for many applications networked computers allowed single computers to form electronic
co- ops.
Defining the fifth generation of computers is somewhat difficult because the field is in its youth. Many advances in the science of computer design and technology are coming together to enable the creation of fifth-generation computers.
Fifth generation computers are totally based on
artificial intelligence. A.I. is robotics, in this machines are development in
such a way that they can behave like human, and each and every statement is not
be given every time. These machines would have their own mind off course development by human
being. These computers are under development and we will use them very soon.
Type of computer ;
1.
Digital
2.
Analog computer
3.
Hybrid computer
·
Digital :
1.
Micro computer
2.
Main frame computer
3.
Super computer
4. Mini computer
1. Digital computer;
The input data is represented by a number. These
are used for the logical and arithmetic operations.
·
Accuracy unlimited.
·
Low speed sequential as well as parallel processing.
·
Output is continuous but it is obtained when computations is completed.
·
The digital computers work upon discontinuous data.
· These computer are used for business and scientific applications.
2. Analog computer;
The input data is a number, infect it is a physical quantity like time, pressure, speed, velocity.
Features of Analog computer:
· Approximately 100% Accuracy
· High speed.
· Output is continuous.
· Time is wasted in signal/data transmission.
· The main advantage of Analog computers is that all calculation take places in parallel and hence these are faster. But the accuracy of Analog computers is poor as compared to digital computers.
· Analog computers are mostly used in engineering and scientific application.
· An electronic weighing scale is an example of Analog computer.
The combination of features of analog and digital computer is called hybrid computer. The main examples are central national defense and passenger flight radar system. They are also used to control robots.
·
Hybrid computers are best to use in hospital, where analog part is
responsible for measurement to patient’s heart beat, blood pressure,
temperature and other vital signs.
·
Hybrid computers are also used in
weather forecasting.
Digital
computers can be generally classified by size and power as follows, through
there is considerable overlap:
Personal computer : A small, single user computer based on a microprocessor . in addition to the microprocess, a personal computers has a keyboard for entering data a monitors for displaying information, and a storage device for saving data.
minicomputer: A multi-user computer capable of supporting
from 10 to hundred of user simultaneously.
Mainframe : A power multi-user computer capable of supporting
many hundreds of or thousands of user simultaneously.
Supercomputer :- An extremely fast computer that can perform
hundred of millions of instructions per second.
👉Common Functional Areas of computers system:-
Now we should move ahead to know actually where we are using computers. Common areas where we use computers are as follows:
·
Internet :- Internet is a network of almost all the computers in the
world. We can browse through much more information than we could do in library
and on single click that is because computer can store enormous amounts of
information. We also have very fast and convenient access to information.
Through E- mail, we can communication with a person sitting thousands of miles
away in seconds. There is chat software that enables one to chat with another
person on a real time basis. Video conferencing tools are becoming readily
available to be common man. There are many websites through which we can read
the latest or old news. There are matrimonial sites through which one can
search for a suitable groom or bride.
· Medicine :- We can diagnose diseases. We can learn the treatment. Software
is used in magnetic resonance imaging to examine the internal organs of the
human body. Software is used for performing surgery. Computers are used to
store patient data.
· Word processing :- Word processing software automatically correct spelling
and grammar mistakes. If the content of a document repeats you don’t have to
type it each time. You can use the copy and paste features. You can printout
documents and make several copies. It is easier to read a word-processed
document than a handwritten one. You can add images to your document.
· Telecommunications :- Software is
widely used here. Also all mobile phones have software embedded in them.
·
Digital video or audio composition:- Anybody owning a computer can now enter the field of media production.
Audio or video composition and editing have become much easier by computers. It
no longer costs lakhs of rupees of equipment to compose music or make a files.
Graphics engineers can use computers to generate short or full- length films or
even to create three- dimensional models. Special effects in science fiction
and action movies are created using computers.
· Banks: All financial transaction are
done by computer software. They provide security, speed and convenience.
· Mathematical calculations:- computer have computing speed of over a million calculation per second. We can perform the biggest of mathematical calculations.
· Reservations:- One can book air tickets or railway and make hotel
reservations online.
· Defence : These is software embedded in almost every weapon. Software is
used for controlling the flight and targeting in ballistic missiles. Software
is used to control access to atomic bombs.
· E- learning :- Instead of a book, it is easier to learn from an E-learning
software.
· Computer in business :- Shops and supermarkets use software, which
calculation the bills. Taxes can be calculations and paid online. Accounting is
done using computers. One can predict future trends of business using
artificial intelligence software. Software is used in major stock markets. One
can do trading online. There are fully automated factories running on software.
· ATM Machines : the computer software authenticates the user and dispenses
cash.
· Robotics : robotics are controlled by software.
· Washing machines\ Microsoft oven:
they operate using software.
· Planning and scheduling: software
can be used to store contact information, generating plans, scheduling appointments
and deadlines.
· Sport: software is used for making umpiring decisions. There are
simulation software using which a sportsperson can practices his skills.
Computer are also used to identify flaws in technique .
·
Airport : pilots train on software
which simulates flying. Even tracing of airplanes is also done using computers.
· Weather Analysis : supercomputers are used to analysis and predict weather.
👉Major Part of Computer
There are
three major parts of computer that should be clear before moving ahead:
1. Hardware : it means the physical
entity of computer, in words it is the part of computer which can be seen and
touched.
2. Software : it is the program that
runs on a computer. Software is made up of instructions that tell the computer
what to do. It is stored on disks in bits and bytes.
3. Firmware : it is a program that is written to the read- only memory (ROM) of a computing device. It is added at the time of manufacturing and it is used to runs user programs on the device.
👉Essential Part of Computer
Our next step is to know the essential parts of a computer.
v CPU(central processing unit)
A central processing unit (CPU) or processor is an electronic
circuit that can execute computers program. The CPU is the brain of the
computer. Sometimes referred to simply as the central processor, but more
commonly called processor, the CPU is where all calculations take places.
The central processing unit (CPU) performs the actual
processing of data. The date process is obtained, via the system bus, form the
main memory. Results from the CPU are then sent back to main memory via. The
system bus. In additions to computation the CPU controls and co-ordinates the
operation of the other major components. The CPU has two main components,
namely: the control unit and the Arithmetic/ logical unit (ALU).
The control unit. :
the control unit (often called a control system or central controller
) directs the various components of a
computer. It reads and interprets (decodes) instructions in the program one by
one. The control system decodes each instructions and turns it into series of
control signals that operate the other parts of the computer. Control systems
in advanced computers many change the order of some instructions so as to
improve performance. Controls the fetching of instructions from the main memory
and the subsequent execution of these instructions. Among other tasks carried
out are the control of input and output devices and the passing of data to the
arithmetic\ Logical unit for computation.
The Arithmetic/
logical unit(ALU) :
The set of arithmetic operations that a particular ALU
supports may be limited to adding and subtracting or might include multiplying
or dividing, trigonometry functions (sine, cosine, etc.) and square roots. Some
can only operate on whole numbers (integers) whilst others use floating point
to represent real numbers-albeit with limited precision. However, any computer
that is capable of performing just the simplest operations can be programmed to
break down the more complex operations into simple steps that it can perform.
Therefore, any computer can be programmed to perform any arithmetic operation-
although it will take more time to do so if its ALU does not directly support
the operation. An ALU may also compare numbers and return Boolean truth values
( true or false) depending on whether one is equal to, greater than or less
than the other(“is 64 greater than 65?”). the CPU can carry out simple
arithmetic operations, comparisons between the result of a calculation and
other values, and the selection of the next instruction for processing. All the
rest of the apparently limitless things a computers can do are built on this
very primitive base by programming.
Motherboard
Motherboard is a the main circuit board of a microcomputer. The motherboard contains the connectors for attaching additional boards. Typically, the motherboard contains the CPU, BIOS, memory, mess storage interfaces serial and parallel ports, expansions slots, and all the controllers required to control standard peripheral devices, such as the display screen, keyboard, and disk drive. Collectively, all these chips that reside on the motherboard are known as the motherboard’s chipset.
On most pc, it is possible to add memory chips directly to
the motherboard. You may also be able to upgrade to a faster pc by replacing
the CPU chip. To add additional core features you may need to replaced the
motherboard entirely.
Computer data storage, often called storage or memory, refers
to computer components, devices, and recording media that retain digital data
used for computing, for some interval of time. Computer data storage provides
one of the core functions of the modern computers, that of information
retention. It is one of the fundamental components of all modern computers, and
coupled with a central processing unit (CPU, a processor) implements the basic
computer model used since the 1940s.
Computer is an electronic machine so it knows only “ON” or
“OFF” i.e. “0” or “1”. All the data in computer, processed or stored is
converted into combination of 0s and 1s. this is called binary notation and 0
or 1 are called bits.
· Bit
is a basic memory unit.
· 1
bytes is unit of data that consist of 8 bits
· 1
kilo byte(kb) equals 1024 bytes.
· 1mega
bytes (mb) equals 1024 kilo bytes
· 1Giga
bytes (GB) equals 1024 mega bytes
· 1
tera byte (tb) equals 1024 giga bytes
· 1
peta byte (pb) equals 1024 tera bytes.
· 1
Exa byte (eb) equals 1024 peta bytes
· 1
zeta byte (zb) equals 1024 Exa bytes
· 1
yotta byte (yb) equals 1024 zetta bytes
· 1
bronto byte (bb) equals to 1024 yotta bytes
· 1
geop bytes equal 1024 bronto bytes.
I/O device
I/o is an
abbreviation of input/ output and refers to the transfer of data to or from an
application. The computer will be of no use unless it is able to communicate
with the outside world. Input/ output devices are required for user to
communicate with the computer. In simple terms, input devices bring information
INTO the computer and output devices bring information OUT of a computer
system. These input/ output devices are also known as peripherals since they
surround the CPU and memory of a computer system.
An input
device converts incoming data and instructions into a pattern of electrical
signals in binary code that are comprehensible to a digital computer. An output
device reverses the process, translating the digitized signals into a form
intelligible to the user.
Expansion slots and expansion cards
When we
purchase a CPU some facilities are given, but perhaps if we want to add some
more facilities such as Advance videos etc, then expansion cards are available
in markets and expansion slots are available in CPU, cards can be inserted in
slots. By this new hardware is attached in your pc, now install this hardware
and use the hardware.
How does computer work
Now we
should emphasis on computer working.
v
A computer usually performs four major operations or functions mentioned
below:
v
Input : this is the process of
computer accepting the data or instructions through input device namely
keyboard for the necessary processing. In this process the raw data is
converted into machine language and fed to CPU ( central processing unit) for
necessary processing.
v
Processing : this is the process of performing operations, such as
arithmetic and logical operations,
Based on
instructions. The CPU takes data and instructions from input device and
processes it. The processed data is then sent to the output or storage unit.
Output :
the processed data (information) from CPU which is in the from of machine language
will be converted to user understandable language (like English ) and then fed
to output device like monitor or printer.
Storage :
the storage unit is used to store the data or information permanently or
temporarily.
Type of Memory
Our next
step is to focus on memory. Here we will consider the types of memory on the
basis of storage type and capability.
1. Primary memory:- Primary storage, presently known as memory,
is the only one directly accessible to the CPU. The CPU continuously reads
instructions stored three and executes them as required. Any data actively
operated on is also stored there in uniform manner.
Two
memories are comprised in primary memory.
A. RAM(random Access memory): random access memory is aa form of computer
data storage. Todays. It takes the form of integrated circuits that allows the
stored data to be accessed in any order (i.e. at random). The work random thus
refers to the fact that any piece of data can be returned in a constant time,
regardless of its physical locations and whether or not it is related to the
previous piece of data. The work RAM is mostly associated with volatile types
of memory ( such as DRAM memory modules) where the information is lost after
the power is switched off. However, many other types of memory are RAM as well
(I,e Random Access memory) including most types of ROM and a kind of flash
memory called NOR- flash.
B. ROM(read only memory):- Read only memory is a class of storage
media used in computers and other electronic devices. Because data storage in
read only memory cannot be modified ( at
least not very quickly or easily), it is mainly used to distribute firmware(
software that is very closely tied to specific hardware, and unlikely to require frequent updates)
In its,
which is fabricated with the desired data permanently stored it, and flash
EEPROM can be erased and re-programmed multiple times: they are still described
as “as read- only memory” (rom) because the reprogramming process is generally
infrequent, comparatively slow, and often does not permit random access writes
to individual memory locations. Despite the simplicity of mask ROM, economies
of scale and field-programmability often make and field-programmability often
make reprogrammable technologies more flexible and inexpensive so mask Rom is
rarely used in new products as of 2017.
2. Secondary memory :- secondary storage,
or storage in popular usage, differs from primary storage in that it is not
directly accessible by the CPU. The computer usually uses its input/output
channels to access secondary storage and transfers the desired data using
intermediate area in primary storage. Secondary storage does not lose the data
when the device is powered down it is non-volatile. Per unit, it is typically
also an order of magnitude less expensive than primary storage. Consequently,
modern computer system typically have an order of magnitude more secondary
storage than primary storage and data is kept for a longer time there. In
modern computers, hard disks are usually used as secondary storage. The time
taken to access a given type of information storage on a hard disk is typically
a few thousandths of a second, or
millions, by contrast, the time taken to access a given byte of information
storage in random access memory is measured in billionths of a second, or
nanoseconds. This illustrates the very significant access time difference which
distinguishes solid-state memory from
rotating magnetic storage devices: hard disks are typically about a millions
times slower than memory. Rotating optical storage devices, such as CD and DVD
drives, have even longer access times.
3. Tertiary storage :- tertiary storage or tertiary memory
provides a third level of storage. Typically it involves a robotic mechanism
which will mount (insert) and dismount removable mass storage media into a
storage devices according to the system’ demands; this data is often copied to
secondary storage before use. It is primarily used for archival of rarely
accessed information since it is much slower than secondary storage (e.g. 5-60)
seconds vs. 1-10 millisecond ). This is primarily useful for extra ordinarily
large data stores, accessed, without human operators. Typical examples include
tape libraries and optical jukeboxes.
When a computer needs
to read information from the tertiary storage, it will first consult a cate
log databases to determine which tape or
disc contain the information. Next, the computer will instruct a robotic arm to
fetch the medium and place it in a drive. When the computer has finished
reading the information, the robotic arm will return the medium to its place in
the library.
4. Off-line storage: off-line storage, also known as disconnected
storage, is a computer data storage on a medium or a device that is not under
the control of a processing unit. The medium is recorded, usually in a
secondary or tertiary storage device, and then physically removed or
disconnected. It must be inserted or connected by a human operator before a
computer can access it again. Unlike tertiary storage, it cannot be accessed
without human interaction. Off- line
storage is used to transfer information, since the detached medium can be
easily physically transports. Additionally in case a disaster, for example a
fire destroys the original data, a medium in a remote location will be probably
unaffected, enabling disaster recovery off-line storage increases a general information security, since it is
physically inaccessible from a computer, and data confidentiality or integrity
cannot be affected by computer-based attack techniques. Also, if the
information stored for archival purposes is accessed seldom or never, off-line
storage is less expensive than tertiary storage. In this modern personal
computers, most secondary and tertiary storage media are also used for off-line
storage. Optical discs and flash memory devices are most popular, and to much
lesser extent removable hard disk drives. In enterprise uses, magnetic taps is
predominant. Older examples are floppy disks, zip disks or punched cards.
Some Widely Used
Memory Devices.
Hard Disks.
A hard disk drive or is a
non- volatile storage devices which store digitally encoded data on
platters with magnetic surfaces. It is the only permeants storage for user
which is available in central processing unit. In other words if we are saving
our data in computer so that we can
retrieve that whenever the computer is
on then we are saving our data in hard disk. Early hard drive disks had removed
media: however, an HDD today is typically a select unit ( except for a filtered
vent hold to equalize air pressure) with fixed media.
Floppy Disks
A floppy disk is a data storage medium that is composed disk
of thin, flexible (floppy)magnetic storage medium encased in a square or
rectangular plastic shell. Floppy disks are read are written by a floppy disk
drive or FDD, floppy disks are available in 8- inch (200mm,) 51/4-inch
(133.5mm), and the newest and most common 31/2- inch (90mm) formatted. While
floppy disk drives still have some limited uses especially, with legacy
industrial computer equipment, the have now been largely superseded by USB
flash drives, external hard drives, CD- ROM AND DVD – Rom. The major
disadvantage of floppy disk is that it is very easy target for viruses and data
storage in floppy corrupts very rapidly. One of thew chief usability problem of
the floppy disk is its vulnerability. Even inside a closed plastic housing the
disk medium is still highly sensitive to dust, condensation and temperature
extremes. As with any magnetic storage, it is also vulnerable to magnetic
fields, Blank floppies have usually been distributed with an extensive set of warning,
cautioning the user not to expose it to conditions which can endanger it.
Compact disk (CD)and
digital versatile disk (DVD)
A compact disk ( also known as a CD) is an optical disk used
to store digital data, originally developed for storing digital audio. The CD ,
available in the market since October 1982, remains the standard physically
medium for sale of commercial audio recording to the present day. Standard CDs have a diameter of 120 mm and can
hold up to 80 minutes to audio( 700MB of data). The mini CD has various
diameter ranging from 60 to 80 mm; they
are sometimes used for CD singles or device drivers, storing up to 24minutes of
audio.
CDs are available in following categories;
a. Compact disk read only memory(CD-ROM)
: CD-ROMs are made of reflective metals; Each disk is approximately 4.5 inches
in diameter and hold over 700 MB of data or 80 minutes of audio.
Data can be written on a CD- ROM at the time of manufacturing
only. No data can be recorded afterwards. Therefore we cannot write or make any
changes into data contained in it.
CD- ROM are typically
used to store software programming.
b. Compact disk- recordable ( CD-R):
CD-R is similar to CD-ROM but it allows us to record our own data. But once
data is been written on it, cannot be removed. CDs that we generally use are
CD-r.
c. Compact disk – rewritable (CD-RW) :
it is a writable disk. It allows us to
write and remove data from CD multiple times. CD- RW discs usually hold 650MB
of data or 74 minutes of audio. CD-RW needs to be blank before reuse. DVD
stands for digital versatile/ video disc, DVDR stands for DVD recordable and DVDRW for DVD rewritable. A
recordable DVD store up to 2 hours of very good quality DVD- video, including
several audio track in formats like stereo or DTS.
DVD size : the DVD sizes can be a bit confusing. There are
basically 4 different DVD sizes,
v DVD-5, this is the most common DVD
media, often called, 4.7 GB media.
v DVD-9, holds arounds 8540000000 bytes
and that is 7.95 GB.
v DVD-10, holds arounds 9400000000
bytes and that is 8.75 GB.
v DVD-18, holds arounds 17080000000
bytes and that is 15.9 GB.
DVD write and read speeds :
§ Single layer (4.7 GB) write speeds
8x( pcav/zclv) = about
8-10 minutes
12x(pcav/zclv ) =
about 6.5-7.5 minutes
16x(cav/zclv) about
6-7 minutes
·
Dual/ double layer (8.5 GB) write speeds
1xCLV= abouts 105 minutes
2.4x CLV= about 27 minutes
·
Single Layer ( 4.7) read speeds
Bx CAV ( avg-6x) read speeds is max 10.57MB/S = ~10minutes
12x CAV (avg 12x) read
speeds is max 15.85MB/s= ~7 minutes
16x CAV (avg 12x) read speeds is max 21.13MB /s= ~5 minutes
Blu-Ray Disc
Blu- ray disc (BD) is a next generation optical disc format
meant for storaging high- density data. The Blu – ray standard was develop by a
groups of PC companies called the blu- ray disc association (BDA). Blu ray has
more information capacity per layer, 25 instead of 15 gigabytes, but may
initially be more expensive to produce.
Ø BD-R single layer 25GB or 7.8GB
Ø BD-R Dual layer 50GBor 15.6GB
Ø BD-RE single layer rewriteable 25 GB or
7.8GB
Ø BD- RE Dual layer rewriteable 50GB
or15GB
Input
devices are used for entering data in the computer. Some of the commonly used
input devices are
Keyboard is the standard input device
attached to all the computers. The keyboard layout is similar to the
traditional Qwerty typewrite. There are some button on keyboard which are
called “keys”. On these keys, characters are printed and by pressing a particular
key that particular character is used. A standard keyboard contains a total of
101 to 104 keys in most cases, each press of a key corresponds to a single
written symbol. However, to produce some special characters, requires pressing
and holding several keys simultaneously or in sequence.
In addition to standard keys, a keyboard
may contain some extra command keys and function keys. These keys do not
produce any symbol, but affect the operation of the computer or the keyboard
itself.
There are various types of keyboard which
are available in market such as multimedia keyboard, internet keyboard, folding
keyboard and wireless keyboard. The following figure : 1.10, shows a standard
and a multimedia keyboard.
Mouse is a very common input device used
with computer. It is a pointing device used to move a graphical pointer on the
screen. This graphical pointer is also known as cursor. Using mouse, we can
give commands, draw images and perform other input tasks. A mouse has two or
three buttons on its top surface. These buttons can be clicked or double-
clicked to perform tasks, like to select an icon on the screen or to open the
selected document.
To today there are several variants of
mouse available in market. One of the most popular is optical mouse. An optical
mouse doesn’t have a ball. It uses a laser to sense the motion of the mouse.
The figure : 1.11 shows an optical mouse.
scanner
Scanner is used to input an outside
picture into compute. The keyboard can input
only text through keys provided in it. If we want to input a picture a keyboard cannot do that. To input a picture
we need a scanner. A scanner is an optical device that analyses images, printed
text, or handwriting and converts it to a digital images. The common scanner
devices are:
Ø
Magnetic
ink character recognition reader (MICR)
Ø
Optical
mark reader(OMR) scanner
Ø
Optical
character recognition (OCR)
Ø
Barcode
reader
MICR Reader: To process large
volumes of cheques and drafts, MICR is widely used by banks. The bottom line on
all cheques and drafts has special character printed in special font called
MICR. Cheques are put inside a MICR
reader.
As they enter the
reading units, the cheques pass through the magnetic field which causes the
read head to recognize the character of the cheques. The figure : 1.12. is an
images of MICR reader.
OMR scanner:- OMR technique is
widely used for students answer sheets. These answer sheets are directly fed to
a computer for grading where OMR is used. The OMR scanner puts a shining beam
of light on the documents and deletes the markets area from unmarked ones. This
is possible because a marked area reflects more light in comparison to an
unmarked area. The above figure: 1.13 is an image of a OMR scanner.
OCR scanner : For direct
reading of any printed character, OCR is used. It translates images of
handwritten or typewritten text, usually captured by a scanner, into
machine-editable text. Let suppose we have a set of hand written documents and
we want them inside computer them this scanner can help us a lot. OCRs are more
expensive than MICR, though they are better than MICR. The following figure :
1.14 is an image of an OCR scanner.
Barcode reader: it is
used to read barcodes printed on most of items we use in our daily life. This
helps in keeping track of items in the store and also reduces the instances of shoplifting. A barcode is a
machine- readable re presentation of information in a visual format on a
surface. This is represented using dark
ink on white substrate to create high and low reflectance which is converted to
1s and 0s, but today they also come in various other pattern such as dots
concentric circles, and text codes hidden within images.
A barcode reader
consists of a light source, a lens and a photo conductor that translates
optical impulses into electrical ones. The figure : 1.15 shows a barcode
reader.
joystick
A joystick is also an
input device. Instead of using the cursor keys or mouse, joystick is used to
control on screen objects or cursor by moving a small lever, called stick. It
is commonly used for controlling player movement in video or computer games.
Most joystick are
configured for two dimensional movement. Moving the stick left or right signals
movement along the X axis, and moving it up (forward ) or down (back) signals
movement along the Y axis. The figure: 1.16, is images of a joystick.
Microphone
A microphone is an also
input devices. It is used to transfer voice in computer, means to record audio
in computer. However, to do this, we also require a sound card installed in our
computer. We can use speech recognition
software with out Microphone to dictate text, navigate programs and select commands.
The above figure: 1.16 shows a microphone.
DIGITAL CAMERA
A digital camera can
also be used as an input device for
capturing and storing still image. We can connect a digital camera to as a
computer and transfer the images from the digital camera directly to the
computer. The figure 1.18 shows a digital camera.
Output Devices
As similar to input
devices required for inputting data, the computer display or prints the output
on device called output devices. Some of
the commonly used output device are:
Visual Display units(VDUs):
The most popular and
standard output device is the visual display unit (VDU), informally called
monitor. It is a piece of electrical equipment which displays images and texts
as generated by a computer without producing a permanent record. A monitor
usually consists of either a cathode ray tube (CRT) or some from of flat panel
such as a TET LCD display. The following figure: 1.19 is an image of a CRT
monitor and figure : 1.20 is an image of a LCD monitor.
The monitor comprises of
a display device, circuitry to generate a viewable image or text from electronic
signals sents by the computer, and an enclosure or case. A VDA can be either
monochrome or colored.
Another widely used
output devices is a printer. It is a device which produces a hard copy of
desired data. A hard copy refers to a permanent human- readable text or
graphics taken on a physical print media such a paper or transparency. Some of
the commonly used printers are.
· Dot matric printer(DMP): A dot matric printer
or impact matric printer refers to a type of computer printer with a print head
that contains a cluster of pins. With each pin strike, a dot is printer on a
paper. Collection of several such dots produces the desired text or images on
the paper. A dot matric printer can be
classified.
· Low
resolution dot matric printer: uses 9 pins
· High
resolution dot matric printer: uses 24 pins
A dot matric printer can
print at a speed of 500 characters per second. Dot matric printers can be used
in low- cost, low-quality applications like cash registers, or in demanding,
very high volume application like invoice printing. The figure: 1.21. is an
image of a dot matric printer.
· Inkjet
Printer : An inkjet printer refers to a type of printer
where the printer sprays small droplets of ink onto the media. These ink
droplets are slightly electrically charged. The ink droplets placement on the
media is then determined by the charge of a cathode an electrode between which
the ink moves towards the media. Inkjet printers can produce both color and
blank and-white printing. They offer printing speed of 2 to 4 ppm ( paper per
minutes) and resolution of 300 to 600 dpi ( dots per inch). Inkjet printers are
really cheap and produce high- quality printouts. Because of this inkjet
printers are the most widely used consumer printers. The figure: 1.22 is an
image of an inkjet printer.
· Dye-Sublimation
printer: A Dye- sublimation printer
refers to a type of printer where the printer uses a printing process that
utilizes heat to transfer dye to a medium, such as a printer paper, plastic
card or poster paper. The process is to lay color at a time using a ribbon that
consists of color panels. Dye- sublimation printers color application and are
less well suited for text. The are commonly used as dedicated consumer photo
printers. The figure 1.23. is n image of a dye sublimation printers.
A plotter is a special graphical printer
that operates by moving a pen over the surface of a paper. It uses mechanical,
inkjet or thermal technology to create lager format images. Because of this,
plotters are widely used for printing technical drawing or CAD application
images. The figure : 1.25 is an images of a plotter.
Speaker are the output device, which are used for
listening the audio results. The computer speaker very widely in terms of price
and range.
Generally speaker have
an LED indicator, a 3.5mm headphone jack, volume controllers that include
controls for bass and treble. The figure
: 1.26 is an images of a speakers.
2 Comments
very good sir
ReplyDeleteGood job
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