2. INPUT DEVICES:
2.1 KEY BOARD
2.4 MAGNETIC INK CHARACTER
2.5 TOUCH SCREEN
2.6 BAR-CODE READER
2.7 VOICE RECOGNITION
3. THE PROCESSOR/CPU
ARITHMETIC & LOGIC UNIT (ALU)
4 UNIT OF MEMORY
4.1 BINARY DIGIT
5.1 HARD DISK
5.3 CARTRIDGE TAPE, DAT
7.2 INKJET PRINTER
7.3 LASER PRINTER
1. WHAT IS A COMPUTER? Top
1.1 Computer is an electronic data processing
device derived from human
Its functioning can be divided into
(i) Input - Accepting data and instructions from the user.
(iv) Output- Displaying, printing and/or storage of the results
computer has separate devices to perform these four functions, viz (I) Input
Devices, (ii) Processing Unit (iii) Secondary Storage devices, (iv) Output
Devices. These physical electronic
components are given known as Hardware.
These function as per the
instructions known as Software.
Thus the hardware devices and Software function in co-ordination as a
system called computer system.
2. Input Devices: Top
Input devices are used to feed data and instructions to the
Computer. Some of the
Common input devices are:
(I) Key Board
(iv) Touch Screen
(v) Magnetic Ink
Character Reader (MICR)
Character Recognition (OCR)
(vii) Bar Code
2.1 KEY BOARD
Computer literate has to understand the
operation of key board as it remains the primary input device to enter
data. In typing mode a cursor appears on
screen - the character typed appears at the place where cursor is and the
cursor moves forward. Different types
of keys on keyboard are:
Alphabet keys There
are used to type alphabets a-z and are similar to
the keys of a typewriter.
Number Keys Ten
number keys above alphabet keys are used to enter numbers 0-9. There is another set of Number keys on right
hand side of keyboard used mainly for data entry. These keys function as Number keys when Number lock key is on
(Indicated by light on Num Lock key).
Otherwise these keys perform the other function labeled on these keys.
Caps Lock key When
caps lock key is on, all alphabets get entered in capital letters.
Shift key Shift
key (located on both sides) is pressed along with another character/key. If the character is pressed alphabet, it
will be Capital (provided caps lock key is off, pressing shift key with Caps
lock key on shall enter alphabets in small case). In other cases the upper character mentioned on the key shall be
Space Bar Key The
long blank key in the lower most row , is used to enter blank spaces between
Enter or Return This key
is pressed after giving instruction for execution of the
Key instruction. In the menu driven packages, this key is
also used to go into the presently selected menu option.
Tab Key is
used to move to the next tab stop.
Escape key signifies ignoring/cancellation of last
(ESC) may be used to end a program or come out of a
Break Key is
used in some programs similar to Esc
Back space key is used
to delete character(s) appearing on left side of the cursor.
Delete (Del) key is used
to delete the character(s) appearing on the cursor and to its right. When delete key is pressed the character at
the place of cursor is deleted and next character to the right, if any, moves left, i.e. to the place of
cursor. This key is also used to delete
the entire matter, file or directory selected in windows environment.
Insert Key activities
insertion of character(s) between existing characters.
Arrow keys are
used to move the cursor in the direction indicated on the key viz. up , down,
right and left. These are also used to
select (highlight) a desired menu option in some menu driven programs.
Home & End Keys are used to move to beginning & end of the
Page Up & are
used to move to next or previous screen/page of
Down Keys the
Control Key is
pressed in conjunction with another key.
It controls a program’s
(Contrl) actions. For example Ctrl C (indicated as ^C) in DOS
means abort and move to C prompt.
Alternate Key is
also used alongwith another character.
It gives an alternate meaning
the key pressed alongwith it.
Cntrl+Alt+Del keys pressed together restart the PC.
Function Keys Function
of these (10 or 12) keys depends upon the software/package being used.
Print Screen key prints
the contents of screen.
Pause key: Temporarily suspends the operations of the current
It is a
small device, which is held in the hand.
By moving it on a flat surface, it controls movement of arrow/cursor on
the screen. It has 2/3 buttons at its
top which are pressed using fingers. It
is generally used in graphic based programs like windows. The icons/start up commands etc are
displayed on the screen. Arrow is taken
to mark/select icon command etc. using left (normally) click button.
are used to scan the information whether graphics or text from a paper. We are using hand held scanners to scan
& feed signature of Account Holders into Computers at computerised
branches. Flat bed scanners are also
available and look similar to photostat machine.
2.4 MAGNETIC INK CHARACTER
The characters written with a special
magnetic Ink can be read using a special machine ‘Reader’ by magnetising
them. This technology is being used for
MICR cheques clearing using machines called “Reader-Sorters” at MICR clearing
centre. These machines also sort the
cheques drawee bank wise etc. by capturing data from MICR band at bottom of the
2.5 TOUCH SCREEN
Input can also be given
to a computer simply by touching the required option on its screen. This technique involves infrared beams and
ultra-sonic acoustic waves, which are interrupted when a finger or object comes
in contact with the sensitive screen.
2.6 BAR-CODE READER
Bar Code is
a pattern of lines/bars. The thickness
of these bars and spaces among them represent data. An optical bar reader recognises and interpret the bar Code.
The commands are
spoken to the computer and/or data entered simply by speaking to the computer.
function of computer viz. Processing is performed by the processor - the brain
of the computer. The computer performs
all the processing as per instructions given to it in the form of small steps
called programs. A processor is
desinged to perform this job of carrying out the instructions. A processor (i) reads and writes information
in the computer’s primary memory, (ii) recognises and executes a series of
commands or instructions given by the programs, and (iii) tells other parts of
the computer what to do. Only the
processor can distinguish between programs and data - the program tells the
processor what to do and it acts on the data.
Computers are named
based upon the processor inside. For
example PC 286, 386, 486, Pentium, P-II, P-III use 80286, 80386, 80486,
Pentium, Pentium-II, Pentium-III processors (from Intel). Pentium III is presently latest. The speed of a processor is measured in Mega
Hertz (MHz) e.g. 500 MHz.
The processor is a small piece of
silicon containing one or more complete electronic circuits. Main components of
a micro processor/ central processing unit, CPU are
& Logic Unit (ALU)
- Control Unit
- Primary storage unit
components of CPU are mounted on main circuit board-motherboard of a micro
3.1 ARITHMETIC & LOGIC UNIT (ALU)
All arithmetic &
logical functions are performed in this part of CPU. It performs basic arithmetic functions viz. Addition,
Subtraction, Multiplication, division.
Other mathematical functions like Trignometric, logarithmic are
performed by using four basic arithmetic functions. ALU also performs logic functions viz. comparison of numbers or
conditions like greater than >, less than <, equal to
= , etc.
also includes group of Registers.
Register is a temporary memory location where data is temporarily stored
3.2 CONTROL UNIT
control unit manages resources of the computer. It contains inbuilt instructions, codes/decodes instructions viz.
interprets instructions received from memory, directs the sequence of events
necessary to execute the instruction and establishes the timings of these
PRIMARY STORAGE UNIT
provides temporary storage for operating system, programs & their data when
the instructions are executed. It is
known as RAM (Random Access Memory). It
is volatile, i.e. all information stored in RAM is lost when there is no power
supply to computer (even for a fraction
`It also contains
permanently stored instructions which tells the computer what to do when it is
switched. Such instructions are stored
on ROM (Read Only Memory) chip. The chip
has a Read only Memory which means that the information on the chip can be read
but not altered nor any information can be stored (written) on it.
4 UNIT OF MEMORY
basic unit for measuring memory is Byte.
One Byte is the memory space occupied by one Character (viz. Alphabet,
Number or any other Character on key board, blank space). Commonly used units of memory are KB
(Kilobyte = 1024 bytes), MB (Megabyte = 1,048,576 bytes), BG(Gega =Billion), TB
(Tera = Trillion). RAM is usually
available as 4 MB, 16 MB, 32 MB, 64 MB, 128 MB etc.
4.1 BINARY DIGIT
Computer being an electronic device identifies signals in the form of pulses
that represent either ‘ON’ or ‘OFF’ conditions. The ‘ON’ and ‘OFF’ conditions are labelled with numbers 1 & 0
respectively. This number system is
called the binary system.
The computer identifies
the characters (alphabets, numbers other symbols) as combinations of eight
zeros and ones. Such one or zero is
known as binary digit. It is the
smallest piece of data that can be recognised and used by the computer. The memory space occupied by one binary
digit is known as a ‘bit’. As in the
example above, a character occupies memory space of one Byte and is a
combination of eight binary digits (0s and 1s), thus 1 Byte = 8 bits.
already explained the primary memory/RAM is used for processing of data &
is volatile. To store the large amount
of data/information & instructions (programs) permanently (or for long
term) following secondary storage devices are used:
5.1 HARD DISK
fixed inside the main computer alongwith CPU.
It has large capacity to store information normally in Gega Bytes (i.e.
billions of characters).
The floppy is a movable storage
media. It is inserted in the FDD (Floppy
Disk Drive) in the CPU/Server to store/write information on it and/or to retrieve/read information from
it. The floppies are available in 2
sizes viz. 5-1/4” and 3-1/2” . But
5-1/4” size has become obsolete. The
memory of a 5-1/4” floppy & 3-1/2” floppy is 1.2 MB and 1.44 MB
A floppy has a read, write notch from where the data is
written on/read from the floppy. A
Floppy has provision for sticking a
label on it to indicate its contents. A
floppy is inserted into floppy drive with label pointing upwards and Read-write
opening getting inserted first. There
is arrow indication on the floppy for insertion. The information is stored on a circular magnetic disk inside the
floppy. The information is read/written
through Read-write opening by movement of pointer inside the floppy drive &
rotation of the magnetic disk.
floppy also has a write protect notch/square which is used to protect the data
tored against deletion, modification or addition. The protectiuve covering on 3-1/2” floppy is of hard
plastic. 3-1/2” floppy also has a
protective metal covering read/write opening/window when not in use. It protects magnetic media from possible
damages while handling, from dust etc.
store data of larger volume, cartridge tapes are used. For this, there should be cartridge Tape
Drive (CTD) in the Server. CTDs are
available in different sizes & have different storage capacity e.g. 120 MB,
tapes are also available & can be used with DAT drive in the Server. These have storage capacity in GB.
5.4 CD - ROM
Compact Disk (CD) is a circular Disk
made of aluminium with a coating of transparent plastic. Data stored on it can only be read by
Computer i.e. it has a Read Only Memory(ROM).
Data is etched using laser beam/writable optical Technology. CDs are used for Software Packages, Movies,
Games etc. It should be protected
against scratches on the shining side
where data is stored.
other storage media can be used as Output as well as Input Devices i.e. Using
computer one can write on these magnetic media as well as read from it. But computers can only read the information stored on CD & not
write on it. One can presently write
only once on CDs - these are not re-writable. WORM - Write once Read Many
6. MONITOR HOME
output from a CPU can be stored on secondary storage device (soft copy), can be
seen on a Monitor, and/or a print out can be taken (Hard copy).
Monitor is also known as VDU (Video Display Unit). Now a days at most of places SVGA (Super
Video Graphic Array) colour monitors are being used. These provide good resolution & support Graphics i.e. it
displays characters as well as images.
7. PRINTERS HOME
7.1 Dot Matrix Printer
Uses tiny dots to print text & graphics by
moving print head across the paper.
Such printers may be using 9 pins or more expensive 24 pins. The print head creates a character by
repeatedly striking these pins against a ribbon. Thus it can be used to cut stencils also. These are mostly used to print text, but can
create graphics also. NLQ (Near Letter
Quality) option can be used to improve quality of printing. Their speed is measured in cps (characters per
7.2 Inkjet Printer
tiny droplets of ink from a nozzle on to the paper to form
characters/image. These are quiet and
produce high-quality image but are costlier than Dot Matrix Printers,
particularly the cartridge.
7.3 Laser Printer
highly focused beams of light to transfer images to paper. It is the most advanced technology and uses
toner for printing. Very good quality
text & graphic is printed at high