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 accepted.

Space Bar Key         The long blank key in the lower most row , is used to enter blank spaces between the characters.

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 instruction.  It

(ESC)                     may be used to end a program or come out of a menu etc.

Break Key               is used in some programs similar to Esc  key.

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 document respectively

Page Up &              are used to move to next or previous screen/page of

Down Keys             the document.

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

(Alt)                      to 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.

(Prt Scrn)

Pause key:              Temporarily suspends the operations of the current program.

2.2     MOUSE

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.

2.3     SCANNERS

Scanners 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 RECOGNITION (MICR)

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 cheques.

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.

2.7     VOICE RECOGNITION SYSTEM

                             The commands are spoken to the computer and/or data entered simply by speaking to the computer.

3.     THE PROCESSOR/CPU                                                                                 Top

The main 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

-        Arithmetic & Logic Unit (ALU)

                             -        Control Unit

                             -        Primary storage unit

          These components of CPU are mounted on main circuit board-motherboard of a micro computer/PC.

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.

          ALU also includes group of Registers.  Register is a temporary memory location where data is temporarily stored during calculations.

3.2     CONTROL UNIT

          The 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 events.

PRIMARY STORAGE UNIT

          It 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 of second). 

                        `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

          The 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

          The 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.

5.     SECONDARY STORAGE/MEMORY                                                          Top

          As 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

          It is fixed inside the main computer alongwith CPU.  It has large capacity to store information normally in Gega Bytes (i.e. billions of characters).

5.2     FLOPPY DISKETTES

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 respectively.

          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.

          A 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.

5.3     CARTRIDGE TAPE, DAT

          To 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, 540 MB.

          DAT 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.

          All 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 Times.

6.     MONITOR                                                                                                  HOME

          The 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 second).

7.2     Inkjet Printer  

Squits 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   

Uses 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 speed.