The input unit is used for entering the data and instruction into the computer for
performing computation of the data. The input unit accepts or reads the list of instructions and
data and converts these instructions and data in computer acceptable form. It supplies the
converted instructions and data to the computer for further processing. The devices used for this
purpose are called as Input Devices. Key Board and Mouse are the important input devices used
in our offices. Light pen, Joy stick, tracker ball, Touch pad, Scanner and Pointing stick are some
of the Input Devices.
After selecting the text as above, bring the mouse pointer at the selected text, press the
left mouse button with the finger and without releasing the finger drag the selected text to any
desired position.
Right clicking:
By pressing and releasing the right mouse button, the short cut menu is activated.
performing computation of the data. The input unit accepts or reads the list of instructions and
data and converts these instructions and data in computer acceptable form. It supplies the
converted instructions and data to the computer for further processing. The devices used for this
purpose are called as Input Devices. Key Board and Mouse are the important input devices used
in our offices. Light pen, Joy stick, tracker ball, Touch pad, Scanner and Pointing stick are some
of the Input Devices.
a) Key Board:
The keys in Computer keyboards are almost similar to the keys in a typewriter but in addition
there are some special operational keys carrying special symbols that help us in giving
instructions to computer.
there are some special operational keys carrying special symbols that help us in giving
instructions to computer.
b) Mouse:
Mouse is an essential component in the modern computers which use Windows and other Graphical Use Interface [GUI] applications. Mouse is a small service in which a small ball is kept inside and the ball touches the pad through a hole at the bottom of the mouse. When the mouse is held in hand pushed along a flat surface [mouse pad], the ball inside the mouse rolls and this movement of the ball is converted into electronic signals and sent to the computer, now we get advanced versions of mouse like optical mouse, scroll mouse cordless mouse etc. using the mouse the cursor [the small blinking vertical line we see in the monitor ] can be moved in any direction. The mouse is used for selecting
part or full text or object, and also for dragging and dropping the selected text or object.
part or full text or object, and also for dragging and dropping the selected text or object.
How to handle the mouse?
When we slide the mouse left across the mouse pad the mouse pointer of the screen
moves left on the screen. When we slide it right the pointer moves right. When the mouse is
moved forward or backward, it causes the pointer to move up and down.
The following actions are performed with the mouse:
Clicking:
Keeping the mouse pointer at any position, if we click the mouse button the cursor will
move to that position.
Selecting:
To select a text for copying or deleting, keeping the mouse pointer at the beginning of the
text, click the mouse button [left button] and without releasing the finger move the mouse till the
end of the text and then release the finger. The text thus selected is highlighted and can be copied
or deleted.
Dragging:moves left on the screen. When we slide it right the pointer moves right. When the mouse is
moved forward or backward, it causes the pointer to move up and down.
The following actions are performed with the mouse:
Clicking:
Keeping the mouse pointer at any position, if we click the mouse button the cursor will
move to that position.
Selecting:
To select a text for copying or deleting, keeping the mouse pointer at the beginning of the
text, click the mouse button [left button] and without releasing the finger move the mouse till the
end of the text and then release the finger. The text thus selected is highlighted and can be copied
or deleted.
After selecting the text as above, bring the mouse pointer at the selected text, press the
left mouse button with the finger and without releasing the finger drag the selected text to any
desired position.
Right clicking:
By pressing and releasing the right mouse button, the short cut menu is activated.
c) Scanner:
Scanner is an image acquisition device connected to the computer, which captures either
an image of a text document or a picture and transfers it into bits of information, which a
computer can understand and manipulate.
an image of a text document or a picture and transfers it into bits of information, which a
computer can understand and manipulate.
How does a scanner work?
The scanner uses a light source, typically a cold cathode lamp to illuminate the scanned
object. The light is then reflected off the object and into Charged Coupled Device [CCD]. The
Charged Coupled Device collects the information, and through a series of electronic devices
converts the analog signal into as series of digital signals which can then be read and processed
by a computer.
object. The light is then reflected off the object and into Charged Coupled Device [CCD]. The
Charged Coupled Device collects the information, and through a series of electronic devices
converts the analog signal into as series of digital signals which can then be read and processed
by a computer.
Uses of scanners:
Optical Character Recognition OCR – We can convert text based document images into
text that can be edited by a word – processing software. Enrich our presentations and documents
by adding images. Convert hard-copy images or documents into a fax format for faxing or for
record purpose. Add scanned images to our e-mil to enrich the content.
Type of scanners: Flatbed Scanner, Sheet fed, Handheld, Card scan.
text that can be edited by a word – processing software. Enrich our presentations and documents
by adding images. Convert hard-copy images or documents into a fax format for faxing or for
record purpose. Add scanned images to our e-mil to enrich the content.
Type of scanners: Flatbed Scanner, Sheet fed, Handheld, Card scan.
- Flatbed Scanner: The flat bed scanner as shown in the illustration is one of the most commonly used and most recommended scanners. This scanner allows the user to place a full piece of paper, book, magazine, photo or any other object onto the bed of the scanner and have the capability to scan that object.A sheet containing text can be scanned using the scanner and saved as an image file. There is
- Sheet fed scanner: This scanner allows us to scan pieces of paper. The sheet fed scanner is a less expensive solution when compared to the flatbed scanner.
- Handheld Scanner: The handheld scanner allows the user to drag over select sections of pages, books, magazines, and other objects scanning only sections. However it can be tedious to drag the handheld correctly which can cause distortion in the image being scanned.
- Card scan Scanner: This scanner is mainly used to scan visiting cards for creating data base of the addresses.
d) Punched cards
Punched cards are still in use as medium for recording data and instructions in the form
of punched holes to denote and then they are sequentially read by the card Reader. The card
Reader sends the data and instructions to the CPU to process them. The punched cards used for
data processing are made generally of 80 columns and 12 rows. Today 96 columns cards are
available. In these cards a hole in punched to represent the binary l. The absence of a hole
represents binary 0. If a card is punched wrongly, it cannot be corrected. Further, the punched
cards are not reusable, i.e., cannot be used for any other data. Many numbers of cards are
required for the computer programs. Such a collection of cards is called a deck. Each card has
the left top corner cut to identify the arrangement of the cards is correct or not. The cards are
read by a Unit called a card Reader. The punched cards are placed in the Read Hopper after
verification. On receiving the command from the control unit the device moves the cards one by
one over two sub-devices. One of which, sense the punched holes (0s and 1s) and transcribes the
pulses to the CPU. Then the output is given as per user specification.
Advantages
1. It is very easy to read data on the cards
2. The cards are less expensive than other storage media.
3. It is much simple to operate.
4. After inserting a card, if an error is detected, the whole system stops functioning.
Disadvantages
1. Punched cards are bulky when put together, so they require large space to store them.
2. The cards are easily damaged and perishable.
3. Transfer of data is relatively very slow.
4. An incorrectly punched card cannot be corrected, it must be replaced.
5. Unit Record machines require manual intervention at every stage.
6. Data is not processed in ordinary language. It has to be translated into something we can
understand.
of punched holes to denote and then they are sequentially read by the card Reader. The card
Reader sends the data and instructions to the CPU to process them. The punched cards used for
data processing are made generally of 80 columns and 12 rows. Today 96 columns cards are
available. In these cards a hole in punched to represent the binary l. The absence of a hole
represents binary 0. If a card is punched wrongly, it cannot be corrected. Further, the punched
cards are not reusable, i.e., cannot be used for any other data. Many numbers of cards are
required for the computer programs. Such a collection of cards is called a deck. Each card has
the left top corner cut to identify the arrangement of the cards is correct or not. The cards are
read by a Unit called a card Reader. The punched cards are placed in the Read Hopper after
verification. On receiving the command from the control unit the device moves the cards one by
one over two sub-devices. One of which, sense the punched holes (0s and 1s) and transcribes the
pulses to the CPU. Then the output is given as per user specification.
Advantages
1. It is very easy to read data on the cards
2. The cards are less expensive than other storage media.
3. It is much simple to operate.
4. After inserting a card, if an error is detected, the whole system stops functioning.
Disadvantages
1. Punched cards are bulky when put together, so they require large space to store them.
2. The cards are easily damaged and perishable.
3. Transfer of data is relatively very slow.
4. An incorrectly punched card cannot be corrected, it must be replaced.
5. Unit Record machines require manual intervention at every stage.
6. Data is not processed in ordinary language. It has to be translated into something we can
understand.
e) Paper Tapes
The punched paper tape is a continuous strip of a paper about one inch wide and up to
300 meters long. The characters are recorded on tape, which may be 5 or 8 as per the design of
the tape. These punched positions are called as channels. It is the oldest media, of input and
output media. Her also, a hole represent 1 and its absence represents 0. Data from the tape is read
through a Tape Recorder per second. The tape comes in various forms viz., Oil paper, dry paper,
metalized paper and laminated paper.
Advantages
1. Compared to the punched card, it is more compact and economic on storage.
2. It is less in weight and easy for mailing etc.
Disadvantages
1. Since the roll is so long, correcting or inserting data can be very tedious process and time
consuming.
2. The life of the paper tape is short. This makes it inconvenient for storing over a long period.
It is not durable.
3. Moreover, it is sequential data processing medium.
300 meters long. The characters are recorded on tape, which may be 5 or 8 as per the design of
the tape. These punched positions are called as channels. It is the oldest media, of input and
output media. Her also, a hole represent 1 and its absence represents 0. Data from the tape is read
through a Tape Recorder per second. The tape comes in various forms viz., Oil paper, dry paper,
metalized paper and laminated paper.
Advantages
1. Compared to the punched card, it is more compact and economic on storage.
2. It is less in weight and easy for mailing etc.
Disadvantages
1. Since the roll is so long, correcting or inserting data can be very tedious process and time
consuming.
2. The life of the paper tape is short. This makes it inconvenient for storing over a long period.
It is not durable.
3. Moreover, it is sequential data processing medium.
f) Magnetic Tape
Because of the problems faced in the paper media, magnetic substances have come. First
among these was the magnetic tape. This is also a sequential media for normally between 1.25-
2cms. Wide and up to 900 meters long. It is made of plastic with a metallic magnetic oxide
coating on one side. Generally, data is recorded on either a 7 parallel-rack-tape or on a 9 paralleltrack-
tape. Writing on and reading from the tape is done with the assistance of READ/WRITE
head. The number of characters per inch length of tape stored is called the 'density' of the tape.
This varies from 550 to 1600 or even 16K. The 9 Track tapes have the higher densities. Then
comparing with the punched card and punched tape, the magnetic tape has certain advantages
and disadvantages.
Advantages
1. Data are stored very compactly.
2. It is very easy to handle the Magnetic Tape than the Deck of Cards.
3. The Magnetic tape costs less than the cards.
4. It requires less storage space for data and therefore has a large capacity.
5. It is reusable i.e., the old data can be wiped out and fresh information could be recorded on it.
6. The speed of transferring the data is very high comparing to paper devices.
Disadvantages
1. In magnetic tapes, the data has to be accessed sequentially. This makes the retrieval of data
slow.
2. The punched cards can be read visually, whereas to read the magnetic tape a I machine is
needed.
3. The tape is subject to the usual wear and tear of time.
4. Data will be erased if the tape is exposed or placed nearby any Magnetic field or high voltage
circuits.
among these was the magnetic tape. This is also a sequential media for normally between 1.25-
2cms. Wide and up to 900 meters long. It is made of plastic with a metallic magnetic oxide
coating on one side. Generally, data is recorded on either a 7 parallel-rack-tape or on a 9 paralleltrack-
tape. Writing on and reading from the tape is done with the assistance of READ/WRITE
head. The number of characters per inch length of tape stored is called the 'density' of the tape.
This varies from 550 to 1600 or even 16K. The 9 Track tapes have the higher densities. Then
comparing with the punched card and punched tape, the magnetic tape has certain advantages
and disadvantages.
Advantages
1. Data are stored very compactly.
2. It is very easy to handle the Magnetic Tape than the Deck of Cards.
3. The Magnetic tape costs less than the cards.
4. It requires less storage space for data and therefore has a large capacity.
5. It is reusable i.e., the old data can be wiped out and fresh information could be recorded on it.
6. The speed of transferring the data is very high comparing to paper devices.
Disadvantages
1. In magnetic tapes, the data has to be accessed sequentially. This makes the retrieval of data
slow.
2. The punched cards can be read visually, whereas to read the magnetic tape a I machine is
needed.
3. The tape is subject to the usual wear and tear of time.
4. Data will be erased if the tape is exposed or placed nearby any Magnetic field or high voltage
circuits.
g. Magnetic Disk
It is yet another step in the evolution of Input/Output devices. The Magnetic Disk has an
advantage over the punched cards and Magnetic Tapes i.e., the data stored on a disk can be read
randomly while in the magnetic tape, the data are read sequentially. Random access is that the
particular record in the file can be detected directly and the access time is saved. In Magnetic
disk the record is accessed in a fraction of second i.e., less than 0.01 sec. The disk varying in
diameter are generally coated on both sides with magnetic oxide. Each surface of the disk is
divided into a number of sectors, called storage segments. The storage segment is a specific
portion of a specific side of the disk. A segment can store one or more record of a file, which will
vary according to the size of the record. While searching, a particular record can randomly be
selected and directly accessed, because, each storage segment is uniquely marked by an address
with side number, track number, sector number etc.
advantage over the punched cards and Magnetic Tapes i.e., the data stored on a disk can be read
randomly while in the magnetic tape, the data are read sequentially. Random access is that the
particular record in the file can be detected directly and the access time is saved. In Magnetic
disk the record is accessed in a fraction of second i.e., less than 0.01 sec. The disk varying in
diameter are generally coated on both sides with magnetic oxide. Each surface of the disk is
divided into a number of sectors, called storage segments. The storage segment is a specific
portion of a specific side of the disk. A segment can store one or more record of a file, which will
vary according to the size of the record. While searching, a particular record can randomly be
selected and directly accessed, because, each storage segment is uniquely marked by an address
with side number, track number, sector number etc.
h. Joysticks and Trackballs
Joysticks provide an alternative method for feeding the computer visually interesting
data. When you move the joystick, cursor on the screen moves in a corresponding way. A
trackball is a plastic sphere mounted in a socket so that it is free to rotate in any direction.
i. Touch Screens
Touch Screens are another favorite "user friendly" method for feeding data into
computer. User can command the computer to perform various useful tasks simply by touching
specific sectors of the screen with their forefingers. The computer senses the Location of the
finger in various ways.
data. When you move the joystick, cursor on the screen moves in a corresponding way. A
trackball is a plastic sphere mounted in a socket so that it is free to rotate in any direction.
i. Touch Screens
Touch Screens are another favorite "user friendly" method for feeding data into
computer. User can command the computer to perform various useful tasks simply by touching
specific sectors of the screen with their forefingers. The computer senses the Location of the
finger in various ways.
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