This document provides an overview of computer components and characteristics. It discusses that computers are programmable machines that can execute prerecorded lists of instructions. Modern computers are electronic and digital, with hardware comprising the physical components and software comprising instructions and data. The main hardware components are the central processing unit (CPU), memory, mass storage devices, input devices, and output devices. The CPU contains the control unit and arithmetic logic unit. Computers can be classified by size and power as personal computers, workstations, minicomputers, mainframes, and supercomputers. The document then discusses characteristics of computers such as speed, accuracy, reliability, storage, retrieval of data/programs, automation, versatility, communications, diligence,

1. MADE BY ANANT AGARWAL CLASS IX-B
ROLL NO.1

3.  Programmable machine. The two principal characteristics of a computer are: It responds to a specific
set of instructions in a well-defined manner. It can execute a prerecorded list of instructions (a
program).
 Modern computers are electronic and digital. The actual machinery -- wires, transistors, and circuits --
is called hardware; the instructions and data are called software
 All general-purpose computers require the following hardware components:
1. Memory : Enables a computer to store , at least temporarily, data and programs.
2. Mass Storage Device: Allows a computer to permanently retain large amounts of data. Common mass
storage devices include disk drives and tape drives.
3. Input Device: Usually a keyboard and mouse, the input device is the conduit through which data and
instructions enter a computer.
4. Output Device: A display screen, printer, or other device that lets you see what the computer has
accomplished.
5. Central Processing Unit (CPU): The heart of the computer, this is the component that actually
executes instructions.

4. Computers can be generally classified by size and power as follows:
1. Personal Computer : A small, single-user computer based on a microprocessor. In addition to
the microprocessor, a personal computer has a keyboard for entering data, a monitor for
displaying information, and a storage device for saving data.
2. Workstation : A powerful, single-user computer. A workstation is like a personal computer,
but it has a more powerful microprocessor and a higher-quality monitor.
3. Minicomputer : A multi-user computer capable of supporting from 10 to hundreds of users
simultaneously.
4. Mainframe : A powerful multi-user computer capable of supporting many hundreds or
thousands of users simultaneously.
5. Supercomputer : An extremely fast computer that can perform hundreds of millions of
instructions per second.

5. 1. Speed
The computer is a very high speed electronic device. The operations on the data inside the computer are
performed through electronic circuits according to the given instructions. The data and instructions flow
along these circuits with high speed that is close to the speed of light. Computer can perform million of
billion of operations on the data in one second. The computer generates signals during the operation
process therefore the speed of computer is usually measure in mega hertz (MHz) or giga hertz (GHz). It
means million cycles units of frequency is hertz per second. Different computers have different speed.
2. Arithmetical and Logical Operations
A computer can perform arithmetical and logical operations. In arithmetic operations, it performs the
addition, subtraction, multiplication and division on the numeric data. In logical operation it compares the
numerical data as well as alphabetical data.
3. Accuracy
In addition to being very fast, computer is also very accurate device. it gives accurate output result provided
that the correct input data and set of instructions are given to the computer. It means that output is totally
depended on the given instructions and input data. If input data is in-correct then the resulting output will
be in-correct. In computer terminology it is known as garbage-in garbage-out.
4. Reliability
The electronic components in modern computer have very low failure rate. The modern computer can
perform very complicated calculations without creating any problem and produces consistent (reliable)
results. In general, computers are very reliable. Many personal computers have never needed a service call.
Communications are also very reliable and generally available whenever needed.

6. 5. Storage
A computer has internal storage (memory) as well as external or secondary storage. In
secondary storage, a large amount of data and programs (set of instructions) can be stored for
future use. The stored data and programs are available any time for processing. Similarly
information downloaded from the internet can be saved on the storage media.
6. Retrieving data and programs
The data and program stored on the storage media can be retrieved very quickly for further
processing. It is also very important feature of a computer.
7. Automation
A computer can automatically perform operations without interfering the user during the
operations. It controls automatically different devices attached with the computer. It executes
automatically the program instructions one by one.
8. Versatility
Versatile means flexible. Modern computer can perform different kind of tasks one by one of
simultaneously. It is the most important feature of computer. At one moment your are playing
game on computer, the next moment you are composing and sending emails etc. In colleges and
universities computers are use to deliver lectures to the students. The talent of computer is
dependent on the software.

7. 9. Communications
Today computer is mostly used to exchange messages or data through computer networks all
over the world. For example the information can be received or send through the internet with
the help of computer. It is most important feature of the modern information technology.
10. Diligence
A computer can continually work for hours without creating any error. It does not get tired while
working after hours of work it performs the operations with the same accuracy as well as speed
as the first one.
11. No Feelings
Computer is an electronic machine. It has no feelings. It detects objects on the basis of
instructions given to it. Based on our feelings, taste, knowledge and experience: we can make
certain decisions and judgments in our daily life. On the other hand, computer can not make
such judgments on their own. Their judgments are totally based on instructions given to them.

8. 12. Consistency
People often have difficulty to repeat their instructions again and again. For example, a lecturer
feels difficulty to repeat a same lecture in a class room again and again. Computer can repeat
actions consistently (again and again) without loosing its concentration:
To run a spell checker (built into a word processor) for checking spellings in a document.
To play multimedia animations for training purposes.
To deliver a lecture through computer in a class room etc.
A computer will carry out the activity with the same way every time. You can listen a lecture or
perform any action again and again.
13. Precision
Computers are not only fast and consistent but they also perform operations very accurately
and precisely. For example, in manual calculations and rounding fractional values (That is value
with decimal point can change the actual result). In computer however, you can keep the
accuracy and precision up to the level, you desire. The length calculations remain always
accurate.

9. Input Devices
The devices that are used to enter data and instructions into the computer are called input devices or units.
In old computers the punched card readers, paper tape readers were used as input devices. Now-a-days the
most commonly used input devices are Keyboard and Mouse.
Output Devices
The computer processes the given input data and gives the output. The devices that are used to get output
from a computer in readable from are called output devices. A number of output devices are available. Some
commonly used output devices are video display units (VDU) and printers.
Central Processing Unit
Central Processing Unit is simply called as CPU. It is the main components of the computer and it is also
called the Processor. The processor used in microcomputer is referred to as Microprocessor. CPU is
considered the brain of the computer. It performs all operations of data according to program's instructions.
It executes the program instructions and tells other parts of the computer what to do. The CPU fetches
instructions of program from main memory and executes them one by one. The CPU also has the ability to
decide which instruction will be executed next. The speed of the CPU is measured in Mega Hertz (MHz) or
Giga (or more).
The CPU is divided into two main part of sub-units. These are:
Control Unit (CU)
Arithmetic Logic Unit (ALU)

10. 1. Control Unit (CU)
The control unit is the most important component of the CPU. It controls and coordinates the
activities of all the other units of the computer. The control unit is considered as the logical hub of
the computer. It acts as a central nervous system for the other components of the computer.
For example the control unit receives the data and instructions from the input device and stores
them in the main memory. It performs all these functions by issuing commands to the relevant
unit of the computer.
The control unit also controls the execution of instructions given to the computer. It fetches the
instructions and data from the memory unit. It decodes and executes the instructions one by one.
2. Arithmetic Logic Unit (ALU)
Arithmetic Logic Unit or simply ALU is another important component of CPU. It performs the
arithmetic and logical operations on the data. When the control unit encounters and instruction
related to perform arithmetic or logical operation on data, it passes that instruction to ALU.
In arithmetic operations ALU performs the addition, subtraction, multiplication and division.
In logical operations ALU compare the numerical data as well as alphabetic data. For example, it
checks whether first number is greater than second, less than second or equal to second etc. It
must be noted that some of the logical operations can be done on test data. For example when
you want to search a word in a document., the CPU matches each word of the document ent with
the given word. Actually the ALU compares each word of document with the given word through
relational equal operator (=).
The ALU consists of a number of registers and adder circuits. A register is a temporary storage
device which holds data and instruction as long as it is being interpreted (decoded) and executed.
When the data and instructions are fetched from main memory for processing, these have to be
stored in one of the registers of the CPU.

11. Input is any data or instructions entered into the computer in the form of signals. The input into the
computer can be entered:
1. Through keyboard (by typing characters).
2. By selecting commands (icons) on the screen and then clicking with mouse.
3. By pressing finger on a touch screen.
4. By speaking into a microphone.
5. By sending image through digital camera.
6. By scanning data printed on paper through scanner etc.
Therefore, the devices that are used to enter data and instructions or commands into the computer are
called input devices or units. The input devices are the eyes and ears of computers. In old computers the
punched card readers, paper tape readers were used as input devices. Now-a-days, the commonly used
input devices are:
1. Keyboard
2. Mouse
3. Touchpad
4. Trackball
5. Joystick
6. Light Pen
7. Digital Scanner
8. Digital Camera
9. Microphone

13. The keyboard is the most commonly used input device. It is used to feed data and instructions into a
computer. It is similar to an electric typewriter. A keyboard contains keys for each alphabetic
characters, digits and special characters. The data and instructions are feed into the computer by pressing
the related keys on the keyboard. The keyboard having some additional keys for specific functions. Keyboard
used with personal computer typically have from 101 to 105 keys.
On laptop and many other handheld computers, the keyboard is built into the top of the system unit.
Usually, these keyboards are smaller in size and have fewer keys such as 85 keys.
Some old type computers have built-in keyboards. Now-a-days, the computer has a separate keyboard. It is
easily plugged in computer. A keyboard is connected to the serial or USB port on the system unit. A standard
computer keyboard is also referred to as QWERTY keyboard. This name represents the first left most letters
on the top alphabetic line of the keyboard spell. Some advanced keyboards do not require the cable to
connect with the cable. They enter data into the computer through wireless technologies such as radio
waves or infrared light waves. These type of keyboards are known as cordless or wireless keyboards.
Keyboard’s may have USB or PS/2 wire port
A keyboard may be divided into four area. There are:
1. Alphanumeric keypad or typewriter area.
2. Numeric keypad.
3. Screen Navigation keys.
4. Editing keys.
5. Function keypad.

14. 1. Alphanumeric Keypad
This area is like a typewrite, it is because this area of keyboard is referred to as Typewriter Area. The user
uses this area to enter general information into the computer. Typists usually use this area of keyboard. This
area consists of:
Alphabetic character keys "A" to "Z" and lower case letters "a" to "z".
Numeric keys "0" to "9".
Many other special keys like Spacebar, Enter key, Ctrl key etc.
2. Numeric Keypad
A set of numeric keys and arithmetic operator keys on the right of keyboard that are similar to calculator
keys is referred to as Numeric Keypad. It also has an extra Enter key and Num Lock key. The Num Lock key is
used to activate or deactivate the numeric keypad. The numeric keypad is mostly used for numeric data
entry.
3. Screen Navigation Keys
The keys that are normally used in word processor or other application programs to move cursor into the
document on the screen are referred to as navigation keys. The most important navigation keys are:
Arrow Keys Used to move the cursor left, right, up and down on the screen. These are also referred to as
cursor keys.
Page Up Key Used to move the cursor one page up of document on the screen.
 Page Down Key Used to move the cursor one page down of document on the screen.
End Key Used to move the cursor to the end of line or to end of screen or document.
Home Key Used to move the cursor to the top left of screen on beginning of document.

15. 4. Editing Keys
The keys that are normally used in word processor or other application programs for editing (modifying) the
document are referred to as editing keys. The most important editing keys are:
Delete Key Used to delete the characters towards the right of cursor position.
Backspace Key Used to delete the characters from the current cursor position toward left.
Enter Key Used to insert new line or paragraph into text editing programs. It is also used to enter selected
command into the computer.
Tab Key Used to insert a tab.
Caps Lock Key Used to change lowercase letters mode to uppercase and vice versa.
Insert Key Used to change insert mode to overwrite mode and vice versa.
5. Function Keys
There are 10 or 12 function keys on the top of keyboard that are labeled as F1, F2,........ F12. These keys are
referred to as Function Keys. These are used to perform special functions. The function of each key depends
upon the software being used on the computer. The designer of the software assigns these keys in his
software as shortcut commands or keys to perform specific task. For example, in most software the function
key F1 is used to get online help about the software running on the computer.

16. Many keyboards also have a Windows Key. When Windows key is presses, Start Menu of Windows is
displayed.
The advanced keyboards also include buttons that allow the user to access the computer's CD or DVD drive.
Adjust speaker volume, open an e-mail program, start a web browser and search the Internet. Some
keyboards also provide the USB ports used to plug the USB device directly to the keyboard instead of system
unit

17. In computing, a mouse (plural mice, or mouse devices.) is a pointing device that functions by detecting two-
dimensional motion relative to its supporting surface. Physically, a mouse consists of an object held under
one of the user's hands, with one or more buttons. It sometimes features other elements, such as "wheels",
which allow the user to perform various system-dependent operations, or extra buttons or features can add
more control or dimensional input. The mouse's motion typically translates into the motion of a cursor on a
display, which allows for fine control of a Graphical User Interface.
The name mouse, originated at the Stanford Research Institute, derives from the resemblance of early
models (which had a cord attached to the rear part of the device, suggesting the idea of a tail) to the
common mouse.
Some high-end mice have 16-bit wide data path. Some high-end mice come with gold-plated USB connector.

18. A light pen is a computer input device in the form of a light-sensitive wand used in conjunction with a
computer's CRT TV set or monitor. It allows the user to point to displayed objects, or draw on the screen, in
a similar way to a touch screen but with greater positional accuracy. A light pen can work with any CRT-
based display, but not with LCD screens projectors and other display devices.
A light pen is fairly simple to implement. Just like a light gun, a light pen works by sensing the sudden small
change in brightness of a point on the screen when the electron gun refreshes that spot. By noting exactly
where the scanning has reached at that moment, the X,Y position of the pen can be resolved. This is usually
achieved by the light pen causing an interrupt, at which point the scan position can be read from a special
register, or computed from a counter or timer. The pen position is updated on every refresh of the screen.

19. Trackball is a pointing device consisting of a ball held by a socket containing sensors to detect a rotation of
the ball about two axes—like an upside-down mouse with an exposed protruding ball. The user rolls the ball
with the thumb, fingers, or the palm of the hand to move a cursor. Large tracker balls are common on CAD
workstations for easy precision. Before the advent of the touchpad, small trackballs were common on
portable computers, where there may be no desk space on which to run a mouse. Some small thumbballs
clip onto the side of the keyboard and have integral buttons with the same function as mouse buttons

20. A joystick is an input device consisting of a stick that pivots on a base and reports its angle or
direction to the device it is controlling. Joysticks are often used to control video games, and
usually have one or more push-buttons whose state can also be read by the computer. A
popular variation of the joystick used on modern video game consoles is the analog stick.
The joystick has been the principal flight control in the cockpit of many aircraft, particularly
military fast jets, where center stick or side-stick location may be employed.
Joysticks are also used for controlling machines such as cranes, trucks, underwater unmanned
vehicles, wheelchairs, surveillance cameras and zero turning radius lawn mowers. Miniature
finger-operated joysticks have been adopted as input devices for smaller electronic equipment
such as mobile phones.

21. In computing, a scanner is a device that optically scans images, printed text, handwriting, or an object, and
converts it to a digital image. Common examples found in offices are variations of the desktop (or flatbed)
scanner where the document is placed on a glass window for scanning. Hand-held scanners, where the
device is moved by hand, have evolved from text scanning "wands" to 3D scanners used for industrial design,
reverse engineering, test and measurement, orthotics, gaming and other applications. Mechanically driven
scanners that move the document are typically used for large-format documents, where a flatbed design
would be impractical.
Modern scanners typically use a charge-coupled device (CCD) or a Contact Image Sensor (CIS) as the image
sensor, whereas older drum scanners use a photomultiplier tube as the image sensor. A rotary scanner, used
for high-speed document scanning, is another type of drum scanner, using a CCD array instead of a
photomultiplier

22. Other types of scanners are planetary scanners, which take photographs of books and documents, and 3D
scanners, for producing three-dimensional models of objects.
Another category of scanner is digital camera scanners, which are based on the concept of reprographic
cameras. Due to increasing resolution and new features such as anti-shake, digital cameras have become an
attractive alternative to regular scanners. While still having disadvantages compared to traditional scanners
(such as distortion, reflections, shadows, low contrast), digital cameras offer advantages such as speed,
portability and gentle digitizing of thick documents without damaging the book spine. New scanning
technologies are combining 3D scanners with digital cameras to create full-color, photo-realistic 3D models
of objects.

23. Magnetic Ink Character Recognition, or MICR, is a character recognition technology used primarily by the
banking industry to facilitate the processing of cheques. The technology allows computers to read
information (such as account numbers) off of printed documents. Unlike barcodes or similar
technologies, however, MICR codes can be easily read by humans.
MICR characters are printed in special typefaces with a magnetic ink or toner, usually containing iron oxide.
As a machine decodes the MICR text, it first magnetizes the characters in the plane of the paper. Then the
characters are then passed over a MICR read head, a device similar to the playback head of a tape recorder.
As each character passes over the head it produces a unique waveform that can be easily identified by the
system.
The use of magnetic printing allows the characters to be read reliably even if they have been overprinted or
obscured by other marks, such as cancellation stamps. The error rate for the magnetic scanning of a typical
check is smaller than with optical character recognition systems. For well printed MICR documents, the
"can't read" rate is usually less than 1% while the substitution rate (misread rate) is in the order of 1 per
100,000 characters.

24. Optical character recognition, usually abbreviated to OCR, is the mechanical or electronic translation of
images of handwritten, typewritten or printed text (usually captured by a scanner) into machine-editable
text. It is used to convert paper books and documents into electronic files, for instance, to computerize an
old record-keeping system in an office, or to serve on a website such as Project Gutenberg. By replacing each
block of pixels that resembles a particular character (such as a letter, digit or punctuation mark) or word with
that character or word, OCR makes it possible to edit printed text, search it for a given word or phrase, store
it more compactly, display or print a copy free of scanning artifacts, and apply such techniques as machine
translation, text-to-speech and text mining to it. OCR is a field of research in pattern recognition, artificial
intelligence and computer vision. Though academic research in the field continues, the focus on OCR has
shifted to implementation of proven techniques. Optical character recognition (using optical techniques such
as mirrors and lenses) and digital character recognition (using scanners and computer algorithms) were
originally considered separate fields. Because very few applications survive that use true optical
techniques, the OCR term has now been broadened to include digital image processing as well.

25. The Optical Mark Reader is a device the "reads" pencil marks on NCS compatible scan forms such as surveys
or test answer forms. If that all seems overly technical to you, just think of it as the machine that checks
multiple choice computer forms. In this document The Optical Mark Reader will be referred to as the
scanner or OMR. The computer test forms designed for the OMR are known as NCS compatible scan forms.
Tests and surveys completed on these forms are read in by the scanner, checked, and the results are saved to
a file. This data file can be converted into an output file of several different formats, depending on which
type of output you desire.
The OMR is a powerful tool that has many features. If you are using casstat (grading tests), the OMR will
print the number of correct answers and the percentage of correct answers at the bottom of each test. It
will also record statistical data about each question. This data is recorded in the output file created when the
forms are scanned

26. A graphics tablet (or digitizing tablet, graphics pad, drawing tablet) is a computer input device that allows
one to hand-draw images and graphics, similar to the way one draws images with a pencil and paper. These
tablets may also be used to capture data or handwritten signatures.
A graphics tablet (also called pen pad or digitizer) consists of a flat surface upon which the user may "draw"
an image using an attached stylus, a pen-like drawing apparatus. The image generally does not appear on the
tablet itself but, rather, is displayed on the computer monitor. Some tablets however, come as a functioning
secondary computer screen that you can interact with directly using the stylus.
Some tablets are intended as a general replacement for a mouse as the primary pointing and navigation
device for desktop computers.

27. A touch screen is a computer display screen that is also an input device. The screens are sensitive to
pressure; a user interacts with the computer by touching pictures or words on the screen. There are three
types of touch screen technology:
Resistive: A resistive touch screen panel is coated with a thin metallic electrically conductive and resistive
layer that causes a change in the electrical current which is registered as a touch event and sent to the
controller for processing. Resistive touch screen panels are generally more affordable but offer only 75%
clarity and the layer can be damaged by sharp objects. Resistive touch screen panels are not affected by
outside elements such as dust or water.

28. Surface wave: Surface wave technology uses ultrasonic waves that pass over the touch screen
panel. When the panel is touched, a portion of the wave is absorbed. This change in the
ultrasonic waves registers the position of the touch event and sends this information to the
controller for processing. Surface wave touch screen panels are the most advanced of the three
types, but they can be damaged by outside elements.
Capacitive: A capacitive touch screen panel is coated with a material that stores electrical
charges. When the panel is touched, a small amount of charge is drawn to the point of contact.
Circuits located at each corner of the panel measure the charge and send the information to the
controller for processing. Capacitive touch screen panels must be touched with a finger unlike
resistive and surface wave panels that can use fingers and stylus. Capacitive touch screens are
not affected by outside elements and have high clarity

29. The processed input data into a useful form is called output when input data is processed, computer
generates several types of output, depending upon the hardware and software used and the requirements
of the user. The user use output on a screen, prints it on the printer or hear it through speakers or head sets.
Therefore, output is normally classifieds as:
Softcopy Output The output received on the display screen or in the audio or video form is called softcopy
output. This kind of output is not tangible and can not the touched. The most popular and commonly used
softcopy output device is display screen .
Hardcopy Output The output printed on the paper is called hardcopy. The printers and plotters devices are
used for this purpose.
Sound Output The output received into the form of sound is called sound output. The speakers are most
commonly used to receive the sound output.
An output device is a hardware component used to get output from the computer. A number of output
devices are available. The commonly used output devices include display device (Monitor), printer, speaker
and headset, fax machine etc.

30. A monitor or display (sometimes called a visual display unit) is an electronic visual display for computers.
The monitor comprises the display device, circuitry, and an enclosure. The display device in modern
monitors is typically a thin film transistor liquid crystal display (TFT-LCD), while older monitors use a cathode
ray tube (CRT).
The size of a display is usually given as the distance between two opposite screen corners. One problem with
this method is that it does not distinguish between the aspect ratios of monitors with identical diagonal
sizes, despite the fact that the area of a given diagonal span decreases as it becomes less square. For
example, a 4:3 21-inch (53.3 cm) monitor has an area of about 211 sq in (1,361 cm2), while a 16:9 21-inch
widescreen has about 188 sq in (1,213 cm2).
This method of measurement is from the first types of CRT television, when round picture tubes were in
common use. Being circular, they only needed to use their diameter to describe their tube size. When round
tubes were used to display rectangular images, the diagonal measurement was equivalent to the round
tube's diameter. This method continued even when cathode ray tubes were manufactured as rounded
rectangles.

31. 1. The Enhanced Graphics Adapter (EGA) : is the IBM PC computer display standard specification located
between CGA and VGA in terms of color and space resolution. Introduced in 1984 by IBM for its new PC-
AT, EGA produces a display of 16 simultaneous colors from a palette of 64 at a resolution of up to
640×350 pixels. The EGA card includes a 16 kilobyte ROM to extend the system BIOS for additional
graphics functions and includes the Motorola MC6845 video address generator as used in the CGA.Each
of the 16 colors can be assigned a unique RGB color code via a palette mechanism in the 640×350 high-
resolution mode; the 64 palette colors are a balanced RGB color set comprising all possible
combinations of two bits per pixel for red, green and blue. EGA also includes full 16-color versions of the
CGA 640×200 and 320×200 graphics modes
2. VGA is referred to as an "array" instead of an "adapter" because it was implemented from the start as a
single chip (an ASIC), replacing the Motorola 6845 and dozens of discrete logic chips that covered the
full-length ISA boards of the MDA, CGA, and EGA. Its single-chip implementation also allowed the VGA to
be placed directly on a PC's motherboard with a minimum of difficulty (it only required video memory,
timing crystals and an external RAMDAC), and the first IBM PS/2 models were equipped with VGA on the
motherboard. (Contrast this with all of the "family one" IBM PC desktop models—the PC [machine-type
5150], PC/XT [5160], and PC AT [5170]—which required a display adapter installed in a slot in order to
connect a monitor.)

32. A computer printer is a computer peripheral device that produces a hard copy (permanent human-readable
text and/or graphics usually on paper) from data stored in a computer connected to it. A virtual printer is a
piece of computer software whose user interface and API resemble that of a printer driver, but which is not
connected with a physical computer printer.
INKJET PRINTER
An inkjet printer is a type of computer printer that reproduces a digital image by propelling variably-sized
droplets of liquid material (ink) onto a page. Inkjet printers are the most common type of printer[1] and range
from small inexpensive consumer models to very large and expensive professional machines.[2]
BARCODE PRINTER
A barcode printer (or bar code printer) is a computer peripheral for printing barcode labels or tags that can
be attached to physical objects. Barcode printers are commonly used to label cartons before shipment, or to
label retail items with UPCs or EANs.
The most common barcode printers employ one of two different printing technologies. Direct thermal
printers use a printhead to generate heat that causes a chemical reaction in specially designed paper that
turns the paper black. Thermal transfer printers also use heat, but instead of reacting the paper, the heat
melts a waxy or resin substance on a ribbon that runs over the label or tag material [1]. The heat transfers
ink from the ribbon to the paper. Direct thermal printers are generally less expensive, but they produce
labels that can become illegible if exposed to heat, direct sunlight, or chemical vapors.
Barcode printers are designed for different markets. Industrial barcode printers are used in large warehouses
and manufacturing facilities. They have large paper capacities, operate faster and have a longer service life.

33. CHARACTER MATRIX PRINTER
Character matrix printers are a category of computer printers (typically impact printers) that
place characters from a fixed character set anywhere onto a fixed grid of possible locations on
the page. Examples of these are daisy wheel printers, golf ball printers, chain printers, and band
printers. A character printer prints one character at a time.
DOT MATRIX PRINTER
A dot matrix printer or impact matrix printer is a type of computer printer with a print head
that runs back and forth, or in an up and down motion, on the page and prints by impact,
striking an ink-soaked cloth ribbon against the paper, much like the print mechanism on a
typewriter. However, unlike a typewriter or daisy wheel printer, letters are drawn out of a dot
matrix, and thus, varied fonts and arbitrary graphics can be produced. Because the printing
involves mechanical pressure, these printers can create carbon copies and carbonless copies.
LETTER QUALITY PRINTER
A letter-quality printer operates in much the same fashion as a typewriter. An array of letters,
numbers, or symbols embossed on a metal surface, are used to strike a ribbon of ink, depositing
the ink on the page and thus printing a character.
LASER PRINTER
A laser printer is a common type of computer printer that rapidly produces high quality text and
graphics on plain paper. As with digital photocopiers and multifunction printers (MFPs), laser
printers employ a xerographic printing process but differ from analog photocopiers in that the
image is produced by the direct scanning of a laser beam across the printer's photoreceptor.

34. THERMAL PRINTER
A thermal printer (or direct thermal printer) produces a printed image by selectively heating
coated thermochromic paper, or thermal paper as it is commonly known, when the paper
passes over the thermal print head. The coating turns black in the areas where it is heated,
producing an image. Two-color direct thermal printers are capable of printing both black and an
additional color (often red), by applying heat at two different temperatures.
Thermal transfer printing is a related method that uses a heat-sensitive ribbon instead of heat-
sensitive paper

35. Plotter
A plotter is a computer printing device for printing vector graphics. In the past, plotters were widely used in
applications such as computer-aided design, though they have generally been replaced with wide-format
conventional printers, and it is now commonplace to refer to such wide-format printers as "plotters," even
though they technically aren't.
Drum Plotter
A drum plotter is also known as Roller Plotter. It consists of a drum or roller on which a paper is placed and
the drum rotates back and forth to produce the graph on the paper. It also consists of mechanical device
known as Robotic Drawing Arm that holds a set of colored ink pens or pencils. The Robotic Drawing Arm
moves side to side as the paper are rolled back and forth through the roller. In this way, a perfect graph or
map is created on the paper. This work is done under the control of computer. Drum Plotters are used to
produce continuous output, such as plotting earthquake activity.
Flatbed Plotter
A flatbed plotter is also known as Table Plotter. It plots on paper that is spread and fixed over a rectangular
flatbed table. The flatbed plotter uses two robotic drawing arms, each of which holds a set of colored ink
pens or pencils. The drawing arms move over the stationary paper and draw the graph on the paper.
Typically, the plot size is equal to the area of a bed. The plot size may be 20- by-50 feet. It is used in the
design of cars, ships, aircrafts, buildings, highways etc. Flatbed plotter is very slow in drawing or printing
graphs. The large and complicated drawing can take several hours to print. The main reason of the slow
printing is due to the movement mechanical devices.
Today, mechanical plotters have been replaced by thermal, electrostatic and ink jet plotters. These systems
are faster and cheaper. They also produce large size drawings.

36. Micrographic plotter
These plotters don’t use drums. The paper or any other medium is held on both sides at the edges by
pinch wheels which give back and forth movement of paper.
Inkjet plotter
These plotters use inkjets in place of ink pens. The paper is placed on a drum and inkjets with different
colored inks are mounted on a carriage. These are capable of producing multicoloured large drawings.

37. A computer has a very large memory. It can store a vast amount of information and can recall that
information instantly and correctly whenever desired. Human beings can do it only to a certain extent.
Whenever a human being acquires new knowledge, the brain subconsciously retains what it feels is
important. This is not the case with a computer. It has a large internal memory. Its memory can store all
the contents of your syllabus and can reproduce them fully or in parts as and when desired by you.
Primary Memory
Primary memory is one of the most important part of the computer, as it determines size and the number of
programs
that can be simultaneously held within the computer and as well as the amount of data that can be
processed quickly.
Primary memory stores necessary programs of system software, which are required to execute user
programs.
The main memory is directly addressed by the CPU.
The main memory can be divided into two parts: .
1. RAM (Random-Access Memory)
2. ROM (Read-Only Memory)
Random-Access Memory (RAM)

38. Random access memory
Random-access memory (usually known by its acronym, RAM) is a form of computer data storage. Today, it
takes the form of integrated circuits that allow stored data to be accessed in any order (i.e., at random). The
word random thus refers to the fact that any piece of data can be returned in a constant time, regardless of
its physical location and whether or not it is related to the previous piece of data. [1]
By contrast, storage devices such as magnetic discs and optical discs rely on the physical movement of the
recording medium or a reading head. In these devices, the movement takes longer than data transfer, and
the retrieval time varies based on the physical location of the next item.
The word RAM is often associated with volatile types of memory (such as DRAM memory modules), where
the information is lost after the power is switched off. Many other types of memory are RAM, too, including
most types of ROM and a type of flash memory called NOR-Flash. Software can "partition" a portion of a
computer's RAM, allowing it to act as a much faster hard drive that is called a RAM disk. Unless the memory
used is non-volatile, a RAM disk loses the stored data when the computer is shut down. However, volatile
memory can retain its data when the computer is shut down if it has a separate power source, usually a
battery.
Read only memory
Read-only memory (usually known by its acronym, ROM) is a class of storage media used in computers and
other electronic devices. Because data stored in ROM 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 strictest sense, ROM refers only to mask ROM (the oldest type of solid state ROM), which is fabricated
with the desired data permanently stored in it, and thus can never be modified. However, more modern
types such as EPROM and flash EEPROM can be erased and re-programmed multiple times; they are still
described 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.

39. Representing Characters in Memory
Information in a computer is stored in the form of strings of O's and 1's. The symbols 0 and 1, known as
binary digits, are called bits. The memory of a computer can be thought of as cells. Each of these cells
contains one bit of information, i.e., each cell will have its state as 0 or 1.
The combination of 8 bits form one byte. Each byte represents one character such as A, B, etc.
Combination of bits is also used to store instructions and data in the computer memory. A nibble is a
combination of 4 bits. It can store one decimal digit in its binary form.
A group of bits representing data or instruction that forms the basic information unit of the computer is
called a word. A word may be of 8, 16, 32, 48 bits or more. The size of the word depends on the architecture
of the computer. A word can also be defined in terms of bytes. Since each byte is a combination of 8 bits, a
word of 16-bit size can be called a 2-byte word. Each word of information is retrieved or stored as a unit in
computer Thus a machine with 16-bit words will be slower than a machine with 32-bit words.
Most microprocessor based computers have 16-bit or 32-bit words.
One byte is the smallest unit which can represent a data item or a character. Other units of memory are
KB, MB, GB, TB.
One Kilobyte (KB) means 210 bytes, i.e., 1024 bytes.
One Megabyte (MB) means 210 KB, i.e., 1024 x 1024 bytes.
One Gigabyte (GB) means 210 MB, i.e., 1024 x 1024 x 1024 bytes.
One Terabyte (TB) means 210 GB, i.e., 1024 x 1024 x 1024·x 1024 bytes.

40. Secondary Memory
Since a computer's main memory is temporary, the secondary memory is used for bulk storage of programs,
data, and other information. It has a much larger capacity than the main memory. The secondary memory is
non-volatile. The two most common secondary storage devices are the floppy disk and the hard disk.
Hard Disk
The hard disk is made up of a collection of disks known as platters . These platters are coated with a material
that allows data to be magnetically recorded. The disks rotate at a very high speed. A typical speed is 3600
revolutions per minute. The read/write head moves across the disk surface. Hard disks can store more data
than floppy disks. Hard disk of size 40 GB is available. They are installed inside the computer and can access
the data more quickly than floppy disks.
Floppy Disks
Floppy disks are individually packed disks. The recording medium on floppies is a myler or vinyl plastic
material with magnetic coating on one or both sides. These plastic disks, coated with magnetic material, are
permanently sealed in a square plastic jacket to protect them from dust and scratches. An elongated slot is
cut in the jacket to enable read/write head access information from anywhere in this slot.
Magnetic Tapes
Magnetic tapes are similar to audio or video tapes except for the difference that magnetic tapes are with
magnetizable material. A large variety of magnetic tapes are available commercially. The older type was
with 1 inch width and 1200 feet length and one foot diameter. Currently smaller size tapes, called
cartridges, are available that are of the size of audio and video cassettes.

41. CD-ROM (Compact Disc-Read-Only Memory)
The CD-ROM stands for Compact Disc-Read-Only Me CD-ROMs are used to distribute a wide variety of
inform from multimedia encyclopedias to books, to games, to image video libraries, to product and sales
presentations, and The advantage is that it is a portable media and can con ..large amount of data.
To read a CD-ROM a device called CD-ROM drive is needed . Any information or data on CD-ROM can be
erased or written onto with the help of a special device called CD recorder.
CD-ROM are available in two forms:
CD-R It is also called as the recordable-CD. It is written once and can be read again and again. Data once
written cannot
be erased.
CD-RW It is also called as erasable-CD. It is a recording system that allows the user to erase previously
recorded
information and then to record new information onto the same physical location on the disk.
DVD (Digital Versatile Discs)
DVD The next generation of CD-ROMs is called DVD-ROM that stands for Digital Versatile Disk. A DVD is the
same size as
a Compact Disc but holds up to 25 times more matter and is much faster. This increased capacity allows DVD
to store
high-quality video as well as higher-than-CD-quality audio. The most notable advantage of DVD is its
capacity.
This allows the ability to access much more data than standard CD-ROM for computer application.

42. Physically, a CD-ROM and a DVD-ROM disk are similar.
DVD represents the first merging of three technologies, namely computer, audio, and television, into one
common format.
Cache Memory
A cache memory is a hardware system used for swapping of information between primary and secondary
storage devices. Generally, data is transferred from the main memory to ALU in computer words, one word
at a time. In cache memory many words from primary memory are transferred to temporary storage area
called cache while CPU is busy in processing the information from the main storage. Now, if information
placed in cache is required by ALU, it can be transferred to it easily. Cache memory is much faster.