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Lecture 3

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					INTRODUCTION TO COMPUTER                                           LECTURE 03

INTERACTING WITH YOUR COMPUTER

INPUT DEVICES.

i)    KEYBOARD
        The keyboard is the primary input device for entering text and numbers.
It is a relatively simple device consists of about 100 keys each of which sends
different codes to the CPU. It was the one of the first peripheral to be used with
PCs, and it is still the most common you will find a keyboard either built into or
attached to every pc.
There are five parts of standard keyboard:
    a) The alphanumeric keys
    b) The numeric keypad
    c) The function keys
    d) Modifier keys
    e) Cursor movement key
How computer accepts input from the keyboard
       When you press a key on a keyboard you might think the keyboard
simply sends that letter to the computer after all, that is what appears to happen.
Actually it is more complex than that.
       A tiny computer chip, called the keyboard controller, notes that a key has
been pressed. The keyboard controller notes that a key has been pressed. The
keyboard controller places a code into a part of its memory called the keyboard
buffer, indicating which key was pressed. This code is called the key’s scan code.
The keyboard controller then signals the computers system software that some
thing has happened at the keyboard. It does not specify what has occurred, just
that some thing has. The signal that keyboard sends to the computer is a special
kind of message called an interrupt request. The keyboard controller sends an
interrupt request to the system software. When it is receive a complete keystroke.
When the system software receives an interrupt request, it evaluates the request
to determine the appropriate response. When a key press has occurred the
system reads the memory location in the keyboard buffer that contains the scan
code of the key that was pressed it then passes the key’s scan code to the CPU.




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PREPARED BY SADIQUE A.BUGTI LECTURER BUITMS
INTRODUCTION TO COMPUTER                                             LECTURE 03



(1) Key is pressed on the keyboard.
                                                            Keyboard



(2) The keyboard controller
sends the scan code for the          Keyboard
key to the keyboard buffer           Controller

(3) The keyboard controller
Sends an interrupt request           Keyboard
to the system software.              Buffer

(4) The system software
represents to the interrupt to the   System
Interrupt by reading the scan  Software
Code from the keyboard buffer.

(5) The system software
 Process the scan code to the CPU
                                          CPU

ii)      THE MOUSE
        A mouse is an input device that rolls around on a fiat surface and control
the pointer. The pointer is an on screen object, usually an arrow that is used to
select text, access menus, move files, or interact with programs, files, or data that
appear on the screen.
A mouse also allows you to create graphic elements on the screen, such as pines,
curves, and free hand shapes.
Using the Mouse
       Every thing you do with a mouse you accomplish by combining pointing
with four other techniques. Clicking, double clicking, dragging, and right
clicking.
The inner working of a mouse
        A mouse is really a really a simple device. The most common type has a
ball inside it that extends just below the housing. When you slide the mouse
around on a fiat surface such as desktop or a mouse pad the ball rolls.
Inside the mouse on two sides of the ball at a 90-degree angle to each other are
two small rollers that touch the ball and spin when the ball rolls.
A sensor detects how much each roller spins and sends this in formation to the
computer. The computer translates the in formation and change the position of
the on screen pointer to correspond to the position indicated by the mouse.




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PREPARED BY SADIQUE A.BUGTI LECTURER BUITMS

				
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Description: Introduction to Computer All 18 Lectures of My Class