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Computer Concept
Lecturer: Jing Liu
Email: [email protected]
Homepage: http://see.xidian.edu.cn/faculty/liujing
Textbook
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E. Balagurusamy, Fundamentals of
Computers, Mc Graw Hill.
Grading
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Final exam: 70%
Others: 30%
Content
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1. Understanding the Computer
2. Computer Organisation and Architecture
3. Memory and Storage Systems
4. Input Devices
5. Output Devices
6. Computer Codes
7. Computer Arithmetic
10. Computer Software
11. Operating Systems
12. Microsoft Software
13. Programming Languages
14. Data Communications and Networks
15. The Internet and World Wide Web
What’s a Computer?
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A computer is an electronic machine
that takes input from the user,
processes the given input and
generates output in the form of useful
information.
What’s a Computer?
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Input: data, programs, user reply
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Data: the raw details that need to be processed to
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generate some useful information.
Programs: the set of instructions that can be
executed by the computer in sequential or nonsequential manner.
User reply: the input provided by the user in
response to a question asked by the computer.
What’s a Computer?
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A computer includes various devices:
Central Processing Unit (CPU)
Monitor
Keyboard and Mouse
What’s a Computer?
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The unique capabilities and
characteristics of a computer:
Speed
Storage capacity
Accuracy
Reliability
Versatility
Diligence
What’s a Computer?
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Limitations:
Garbage-In, Garbage-Out
Dumb machine
Evolution of Computers
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Manual Computing Devices: Sand table,
Abacus, …
Automated Computing Devices: difference
engine, analytical engine, Colossus, …
Charles Babbage: A professor of
mathematics a the Cambridge University is
considered to be the father of modern
computer.
Generations of Computers
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First Generation Computers
• Employed during the period 1940-1956
• Used the vacuum tubes technology for calculation as
well as for storage and control purpose.
• Advantages: (1) Fastest computing devices of their
time; (2) These computers were able to execute
complex mathematical problems in an efficient
manner.
Generations of Computers
•Disadvantages:
(1) The functioning of these computers depended on the machine
language.
(2) There were generally designed as special-purpose computers.
(3) The use of vacuum tube technology make these computers
very large and bulky.
(4) They were not easily transferable from one place to another
due to their huge size and also required to be placed in cool places.
(5) They were single tasking because they could execute only one
program at a time.
(6) The generated huge amount of heat and hence were prone to
hardware faults.
Generations of Computers
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Second Generation Computers
Employed during the period 1956-1963
Use transistors in place of vacuum tubes in building
the basic logic circuits.
Advantages: (1) Fastest computing devices of their
time; (2) Easy to program because of the use
assembly language; (3) Could be transferred from
one place to other very easily because they were
small and light; (4) Require very less power in
carrying out their operations; (5) More reliable, did
not require maintenance at regular intervals of time.
Generations of Computers
•Disadvantages:
(1)The input and output media were not
improved to a considerable extent
(2) Required to be placed in air-conditioned
places
(3) The cost of these computers was very high
and they were beyond the reach of home users
(4) Special-purpose computers and could
execute only specific applications
Generations of Computers
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Third Generation Computers
• Employed during the period 1964-1975
• Use of Integrated Circuits
• Advantages: (1) Fastest computing devices; (2) Very
productive; (3) Easily transportable from one place to
another because of their small size; (4) Use highlevel languages; (5) Could be installed very easily
and required less space; (6) Can execute any type of
application. (7) More reliable and require less
frequent maintenance schedules.
Generations of Computers
Disadvantages:
(1)The storage capacity of these computers was still
very small;
(2) The performance of these computers degraded
while executing large applications, involving complex
computations because of the small storage capacity;
(3) The cost of these computers was very high;
(4) They were still required to be placed in airconditioned places.
Generations of Computers
Fourth Generation Computers
• Employed during 1975-1989
• Use of Large Scale Integration technology
and Very Large Scale Integration technology
• The term Personal Computer (PC) became
known to the people during this era.
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Generations of Computers
Advantages:
(1) Very powerful in terms of their processing speed
and access time;
(2) Storage capacity was very large and faster;
(3) Highly reliable and required very less maintenance;
(4) User-friendly environment;
(5) Programs written on these computers were highly
portable;
(6) Versatile and suitable for every type of applications;
(7) Require very less power to operate.
Generations of Computers
Disadvantages:
(1) The soldering of LSI and VLSI chips on the
wiring board was not an easy task and required
complicated technologies to bind these chips on
the wiring board;
(2) The working of these computers is still
dependent on the instructions given by the
programmer.
Generations of Computers
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Fifth Generation Computers
• The different types of modern digital
computers come under this category.
• Use Ultra Large Scale Integration technology
that allows almost ten million electronic
components to be fabricated on one small
chip.
Generations of Computers
Advantages:
(1) Fastest and powerful computers till date;
(2) Being able to execute a large number of applications
at the same time and that too at a very high speed;
(3) Decreasing the size of these computers to a large
extent;
(4)The users of these computers find it very
comfortable to use them because of the several
additional multimedia features;
(5) They are versatile for communications and resource
sharing.
Classification of Computers
We can classify the computers
according to the following three criteria:
(1) Based on operating principles
(2) Based on applications
(3) Based on size and capability
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Classification of Computers
(1) Based on operating principles:
Analog computers: represent data in the
form of continuous electrical signals having a
specific magnitude
Digital computers: store and process data in
the digital form.
Hybrid computers: a combination of analog
computer and digital computer because it
encompasses the best features of both.
Classification of Computers
(2) Based on applications:
General purpose computers: can work
in all environments.
Special purpose computers: can
perform only a specified task.
Classification of Computers
(3) Based on size and capability
Microcomputers: Designed to be used by
individuals.
Mini Computers: Can handle more data and
more input and output than micro computers.
Mainframe Computers: A very large
computer
Super Computers: The fastest type of
computer that can perform complex operations
at a very high speed.
Computing concepts
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Accepting the raw data
Processing the data
Storing the data
Delivering the output
The Computer System
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Hardware
Software
Data
People
Computer Organisation and
Architecture
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Computer architecture: the definition of
basic attributes of hardware components and
their interconnections, in order to achieve
certain specified goals in terms of functions
and performance.
Computer organisation: the design and
physical arrangement of various hardware
units to work in tandem, in a orderly manner,
in order to achieve the goals specified in the
architecture.
Central Processing Unit
The main operations of the CPU include four
phases:
(1) Fetching instructions from the memory
(2) Decoding the instructions to decide what
operations to be performed
(3) Executing the instructions
(4) Storing the results back in the memory
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Central Processing Unit
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Registers
Arithmetic Unit
Logic Unit
Control Unit
Arithmetic Unit
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Arithmetic Unit is a part of the CPU that
performs arithmetic operations on the
data. The arithmetic operations can be
addition, subtraction, multiplication or
division.
Logic Unit
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Logic Unit is a part of the CPU that
performs logical operations on the data.
Control Unit
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Control Unit is an important component
of CPU that controls the flow of data
and information. It maintains the
sequence of operations being
performed by the CPU.
Main Memory Unit
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The main memory is referred to as the
internal memory of primary memory of
the computer. It is also known as
Random Access Memory (RAM).
Cache Memory
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Cache memory is a small, fast and
expensive memory that stores the
copies of data that needs to be
accessed frequently from the main
memory.
Registers
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CPU contains a few special purpose,
temporary storage units known as
registers. They are high-speed memory
locations used for holding instructions,
data and intermediate results that are
currently being processed.
Internal Communications
The internal communication of a
processor in the computer system can
be divided into two major categories:
(1) Processor to memory communication
(2) Processor to I/O devices
communication
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Processor to Memory
Communication
The direct communication between the
processor and memory of the computer
system is implemented with the help of two
registers:
(1) Memory Address Register
(2) Memory Buffer Register
The reading and writing operations performed
by the processor are called memory read and
memory write operations.
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Processor to I/O Devices
Communication
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The communication between I/O
devices and processor of the computer
system is implemented using an
interface unit. The interface unit acts as
an intermediary between the processor
and the device controllers of various
peripheral devices in the computer
system.
Machine Cycle
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The cycle during which a machine
language instruction is executed by the
processor of the computer system is
known as machine cycle.
Instruction Cycle
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Fetching: The CPU retrieves the
instruction from the main memory of
the computer system.
Decoding: Breaking down the
instruction into different parts, so that it
can be easily understood before being
processed by the CPU.
Execution Cycle
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Executing: The decoded instruction
is executed by the ALU of the CPU.
Storing: The result computed in the
execution phase is either sent to the
memory or to an output device.
The Bus
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A bus is a set of wires that is used to connect the
different internal components of the computer
system for the purpose of transferring data as well
addresses amongst them.
Data bus: used to transfer data amongst the
different internal components. Modern computer
systems use 32-bit data buses for data transfer.
Address bus: transfers the memory addresses for
read and write memory operations.
Memory and Storage Systems
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Primary Memory: Storing the data
that are being currently handled by the
CPU; generally known as “memory”;
Secondary Memory: Storing the
results and the data for future use;
generally known as “storage”;
Internal Process Memory: Placed
either inside the CPU or near the CPU.
Memory Representation
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In the memory, values are represented by
sequences of binary digits, know as bits. Most
computers use a group of eight bits, known
as a byte, to represent a character.
Memory is a “bunch” of bytes or cells into
which we can place data. Each cell, known as
a data item, is assigned a unique number
known as “address”. The CPU can identify
each cell by its address.
Memory Representation
The byte is defined as the “smallest addressable unit”
of memory. Most computers use groups of bytes,
usually 2 or 4, known as “words” to represent
information.
 Computer memories are often rated in terms of their
capacity to store information. Typically, capacities are
described using the unit of byte as follows:
(1) 1 KB (Kilobyte)=1,024 bytes
(2) 1 MB (Megabyte)=1,048,576 bytes
(3) 1 GB (Gigabyte)=1,073,741,824 bytes
(4) 1 TB (Terabyte)=1,099,511,627,776 bytes
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Random Access Memory
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Random Access Memory (RAM) is a volatile
memory and loses all its data when the
power is switched off.
It is the main memory of the computer
system that stores the data temporarily and
allows the data to be accessed in any order.
RAM can be categorised into two main types,
namely, Static RAM and Dynamic RAM.
Random Access Memory
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Static RAM: is a type of RAM in which data is stored
till the power of the computer system is switched on.
SRAM uses a number of transistors to store a single
bit of digital information.
Dynamic RAM: is the RAM in which data is stored in
a storage cell, consisting of a transistor and a
capacitor. The DRAM needs to be continuously
refreshed with power supply because the capacitor
has the tendency to get discharged. DRAM retains
the data for a very short span of time, even after the
power supply is switched off.
Read Only Memory
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ROM is the memory that stores the data
permanently.
The data can be easily read from this type of
memory but cannot be changed.
ROM is most commonly used in devices such
as calculators, laser printers, etc.
ROM does not allow the random access of
data, and allows sequential access of data.
Read Only Memory
ROM is divided into four types:
(1) Programmable ROM: a memory chip on which the write
operation of data can be performed only once. PROM is reliable
and stores the data permanently without making any change in
it. It is mostly used in video games and electronic dictionaries.
(2) Erasable PROM: a type of ROM in which data can be
erased or destroyed using Ultraviolet Light.
(3) Electrically Erasable PROM: a type of ROM in which data
can be erased or destroyed by exposing it to an electric charge.
(4) Flash ROM: a type of EEPROM that stores the information
using floating-gate transistors, which can store electric charge
for a longer period of time as compared to the normal
transistors. This memory is mainly used in the memory cards of
mobile phones, digital cameras and ipods for storing data. Flash
ROM has faster speed of reading data, as compared to any
other type of ROM.
Storage Systems
Storage systems are the devices used for
data storage. The main objective of the
storage system is to permanently store data.
The storage systems can be classified as
follows:
(1) Magnetic
(2) Optical
(3) Solid state
(4) Magneto Optical
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Magnetic Storage Systems
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Magnetic storage systems can be defined as
the storage systems that store the data on a
magnetised medium, with the help of
magnetised particles. Magnetic tapes,
magnetic disks, hard disks, floppy disks are
examples of magnetic storage systems.
Can store any type of data, such as text,
audio, video, image
Magnetic Storage Systems
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Magnetic tapes: The plastic tapes with magnetic
coating that are used for storing the data. They are
similar to the normal recording tapes. The data
stored on the magnetic tapes can be accessed using
the sequential access method.
Magnetic Disks: A flat disk that is covered with
magnetic coating for holding information. It is used
to store digital information in the form of small and
magnetised needles. These needles help in encoding
a single bit of information by getting polarized in one
direction represented by 1, and opposite direction
represented by 0. It allows the random access of
data and provides the facility of erasing and rerecording the data as many times as required.
Optical Storage Systems
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The optical storage systems use the
laser light as the optical medium to
retrieve as well as record data.
The optical storage devices are either
read-only or writable.
Solid-State Storage Devices
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Solid-state Storage Devices were developed
in 1978 by Storage Tek Company.
Do not use magnetic and optical medium to
store data. Instead, use the semiconductor
devices.
Contains all the properties of hard disk drives
to store the data and use solid-state memory,
which has no moving parts.
The examples of SSD are flash memory cards
and Universal Serial Bus (USB) devices.
Storage Evaluation Criteria
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Access Mode: random access mode, sequential
access mode, direct access mode
Access Time: the time taken by the processor in
completing the requests made by the user for
performing the read and write operations.
Storage Capacity: the size of the memory available
for storing the data, and measured in terms of bytes.
Storage Type: Temporary and permanent memory.
Cost: the cost of the storage device used in the
computer system for holding the data.
Input Devices
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Input devices are electromechanical devices
that are used to provide data to a computer
for storing and further processing, if
necessary.
We can provide the input to a computer in
two ways: (1) Manually through devices such
as keyboard and mouse; (2) Directly from
documents using devices such as scanners.
Input Devices
Depending upon the type or method of input,
the input device may belong to one of the
following categories:
(1) Keyboard
(2) Pointing devices
(3) Scanning devices
(4) Optical recognition devices
(5) Digital camera
(6) Voice recognition devices
(7) Media input devices
Keyboard
Keyboard is the most commonly used input device. We can use a
keyboard to type data and text and execute commands. A standard
keyboard consists of the following groups of keys:
(1) Alphanumeric keys: The alphanumeric keys include the
number keys and alphabet keys. These keys are arranged in the
same style as in the normal typewriters, popularly known as
QWERTY layout;
(2) Function keys: Arranged in a row on the top of the keyboard.
Help perform specific tasks, such as searching a file or refreshing a
web page;
(3) Central keys: Used for controlling the movement of cursor
and screen display. Include arrow keys, modifier keys such as
SHIFT, ALT, CTRL;
(4) Numeric keypad: Located on the right side of the keyboard.
This looks like a calculator’s keypad;
(5) Special purpose keys: Escape, Insert, Delete, Print Screen,
Pause, Tab, Spacebar;
Pointing Devices
Pointing devices are the input devices that are generally
used for moving the cursor to a particular location to
point an object on the screen. With the help of pointing
devices, we can easily select the icons, menus, windows,
etc on the Graphical User Interface. Some of the
commonly used pointing devices are:
(1) Mouse
(2) Trackball
(3) Light pen
(4) Joystick
(5) Touchscreen
Mouse
A small hand-held pointing device that
basically controls the two-dimensional
movement of the cursor on the displayed
screen. The most commonly used types
of mouse are:
(1) Mechanical mouse
(2) Optical mouse
Scanning Devices
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Scanning devices are the input devices that
can electronically capture text and images,
and convert them into computer readable
form.
The basic task of a scanning devices is to
convert an image or the textual data into
digital data, i.e., in the form of boxes, where
each box represents either zero or one. The
resultant matrix is known as bit map and is
displayed on the screen.
Scanning Devices
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The scanning devices can be differentiated from each
other on the basis of the following characteristics:
• Resolution: the closeness of the pixels in the bit
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map, and vary from 72 to 600 dots per inch (dpi);
Size: the small sized scanning device can scan
approximately two to five inches of the document,
whereas the large sized one can scan approximately
up to forty inches of the document.
Scanning Devices
• Scanning technology: Some ones use Charged
Coupled Device (CCD) arrays, whereas others use
Photo Multiplier Tubes (PMT) technology. The CCD
consists of a series of light receptors, which are
sensitive to the variation in the light frequency. As
the frequency of light changes, these scanning
devices detect the change and the output obtained
after scanning also gets accordingly changed. The
PMT consists of a photocathode, which is a
photosensitive surface used for generating the
electrons. PMT is used for identifying the light
emitted by the weak signals.
Scanning Devices
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On the basis of these characteristics, the scanning
devices can be categorized as follows:
• Hand-held scanners: are suitable for scanning
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small images rather than the whole page of text or
pictures, and are generally used for identifying the
bar-code label of the products.
Flat-bed scanners: consist of a flat surface
composing of glass pane on which the documents are
kept for scanning. Under this glass pane, there is
xenon light and a CCD, which consists of an array of
red, green and blue filters.
Scanning Devices
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Drum scanners: consist of a large drum, which is
used for scanning the documents. These scanners
make use of the PMT technology, instead of the CCD
technology. The resolution image of these scanners is
very high, ranges form 8000 dpi to 11000 dpi.
Slide scanners: are used for scanning slides as well
as film negatives. These scanners are also known as
film scanners as they can easily scan the original
image of the film. The dark areas appear light and
the light areas appear dark.
Optical Recognition Devices
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Optical recognition devices are used for recognising
the characters optically. The optical recognition
devices basically make use of optical scanner for
inputting data. Unlike keyboards, the optical
recognition devices do not enter the data by
pressing the keys. They help the users in saving a
lot of time. Commonly used optical recognition
devices are:
Optical Character Recognition (OCR) devices:
scan a particular document by recognizing its
individual characters and converting it into the
editable form.
Optical Recognition Devices
• Optical Mark Recognition (OMR) devices: help
in obtaining the data from the marked fields. These
devices prove to be of great use in recognizing
characters in question sheets, enrolment forms,
registration forms, employee payroll, etc. Most
popularly, the OMR devices are used for scanning the
documents having multiple choices as in the question
papers used in schools, colleges, etc.
Optical Recognition Devices
• Magnetic Ink Character Recognition (MICR)
devices: special devices used for recognizing the
characters written with magnetic ink consisting of
iron oxide particles. These devices were specially
developed for the banking operations. The details on
the bank cheques, such as cheque number, bank and
branch code are written with the magnetic.
Digital Camera
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A digital camera is a handheld electronic device that
is used to capture the image of an object
electronically. The digital camera consists of a built-in
computer, which helps in recording the images
electronically. The following are the main features of
the digital camera:
• Capturing and storing thousands of images on a
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single memory chip
Editing as well as deleting the images
Recording the video clip with sound
Showing the just recorded video clip on the camera
screen
Digital Camera
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The image captured by a digital camera is in the
digital format and can be easily downloaded on a
computer system.
The quality of the pictures captured by a digital
camera depends on the resolution factor. The more
the resolution of a digital camera, the better is the
image quality.
Voice Recognition System
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The voice recognition devices generally record the
voice of a person and transform it into electrical
signals. The electrical signals are then converted into
the machine readable code.
The voice recognition system only recognises the
voice of the speaking person rather than what he
speaks.
The voice recognition devices are used for various
purposes such as dictation, training air-traffic
controllers, etc. These systems allow users to
communicate with computers directly without using a
keyboard or mouse.
Data Acquisition Sensors
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Sensors are the devices that are used for
detecting and measuring the physical
quantities, such as heat, temperature, and
converting them into electrical signals. The
sensors are most commonly used in data
acquisition systems.
The data acquisition system collects the
electrical signals from various devices and
converts them into the digital signals for
further assessment.
Media Input Devices
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The input devices, which are generally used in
media for communicating with the mass
audiences, are known as media input devices.
The following are the most popularly used
media input devices:
• Microphone
• Webcam
• Graphics tablet
Output Devices
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Output devices receive the processed data (information)
from the CPU and present it to the user in a desired form.
They act as an interface between the computer and the
user. The main task of an output device is to convert the
machine readable information into human-readable from
which may be in the form of text, graphics, audio or video.
Depending upon the form of output required, the output
device may belong to one of the following categories:
Display monitors
Printers
Plotters
Voice output systems
Projectors
Output Devices
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While the printers and plotters provide the physical
form of output known as hard copy, the display
monitors, voice output systems and projectors
provide temporary output known as soft copy. Unlike
hard copy, soft copy is not a permanent form of
output.
Display Monitors
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Earlier the display monitors were capable of
displaying the characters only in a single font and in
a single color. These characters were arranged in a
rectangular grid on the screen.
The display screens, which are available today,
support many fonts and colors.
Different types of display monitors use different
technology for displaying the data.
Display Monitors
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Cathode Ray Tube (CRT) Monitor: contain an
empty glass tube with a phosphor coated fluorescent
screen and a source of electrons known as electron
gun. A CRT monitor has many advantages, such as a
high contrast ratio and color depth. It also provides a
change in the resolution without affecting the clarity
of the picture. But it is very bulky and occupies a lot
of space on the desk. It also consumes a lot of power
and produces a large amount heat.
Display Monitors
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Liquid Crystal Display (LCD) Monitor: Use liquid
crystals technology to display the images. An LCD
monitor is small in size and light in weight so it
occupies less space on the desk. Also, the power
consumption by an LCD monitor is very less. However,
it has a weak color quality as compared to a CRT
monitor.
Thin Film Transistor (TFT) Monitor: A TFT
monitor is similar to an LCD monitor except for one
difference that it uses thin film transistor technology
along with liquid crystal technology to improve the
quality of the image.
Printers
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A printer is a computer hardware that generates the hard
copy of the information processed by a computer system.
• Impact Printers: there exists a mechanical contact
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between print head and paper. Print head is the part of
the printer that resembles a hammer and is responsible
for transferring the ink to the paper in the form of
required characters. Impact printer contains an individual
print head for each character.
Non-Impact Printers: there exists no mechanical
contact between the print head and paper. These printers
spray ink on the paper with the help of a nozzle. The
most popular ones are ink-jet printers and laser printers.
Plotters
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Plotter is a device used to print high quality graphics
and images. It uses one or more pens to produce a
high quality drawing. These pens change their
positions and draw continuous lines to produce an
image. The plotters were used as a substitute to the
colored printers when the printers were very
expensive and were also not capable of drawing
bigger images such as graphs.
Voice Output Systems
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Voice output systems record the simple messages in
human speech form and then combine all these
simple messages to form a single message. The voice
response system is of two types: (1) a reproduction
of human voice and other sounds; (2) speech
synthesis.
The basic application of a voice output system is in
Interactive Voice Response systems, which are used
by the customer care or customer support
departments of an organization, such as
telecommunication companies, etc.
Projectors
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A projector is a device that is connected to a
computer or a video device for projecting an image
from the computer or video device onto the big white
screen.
A projector consists of an optic system, a light source
and displays, which contain the original images.
Projects were initially used for showing films but now
they are used on a large scale for displaying
presentations in various situations.