keyboard

keyboard

keyboard:

Programs and data are entered into a computer through a key-board which is attached to a computer. A keyboard is similar to the keyboard of a typewriter. It contains alphabets, digits, special characters, function keys and some control keys. When a key is pressed, an electronic signal is produced which is detected by an electronic circuit called keyboard encoder . A computer includes all the keys found on a typewriter plus some additional keys. These additional keys are cursor control (i.e. moving the cursor around on the screen), insert, delete, and scroll control keys. There are a total of 101 keys (some have more). At the right side of the keyboard is the numeric keypad with numbers and basic mathematical symbols. 

keyboard daigram

    Numeric keypad can also be used for cursor control. This double function of numeric keypad is controlled by ( Num Lock ) key. 

The keyboard contains a small built-in processor. When you pre a key, the keyboard processor detects it and sends a number (binary nurnber) corresponding to that key (scan code) to the key-board cotitlIcr, located on the motherboard. This code is then finally transmitted to the processor (CPU). The CPU then processes it using a program called keyboard driver. The keyboard driver translates the codes into their corresponding characters. Different types of keys ind their functions are described in the following Sections.

    Standard Typewriter kays:

PC keyboard has a set of keys that closely resemble the keys found on a typewriter. These include the numeric keys (0 to 9), character keys (A to Z), special characters (!, @, #, $, etc.). These keys are often called QWERTY keys (named after the top row of letters).

    Function Keys:

Keys labelled as F1 to F12 carry out special functions in the soft-ware running in the PC. For example, the F1 key in most pro-grams displays the help file available for using that program.

   Cursor Movernenf Keys:

These ←, →, ↑, ↓arrow keys are used to move a cursor (a blinking line on the tivelyonitor) to the left, right, up or down respectively. In addition, there are four more keys, PGUP, PGDOWN, HOME, and END. This keys let you move the cursor quick throught text. The HOME and END keys are specially used for positioning the cursor at the 101 keys model of the keyboard, there is a separate set of cursor movement keys, namely ←, →, ↑, ↓ arrow keys. But in the case of old type 83 keys model of the key-board, you\need to press ( Num lock) key to change over between the numeric and cursor movement functions of the keys. 

Computer organization (cpu)

What is Computer Organization:

The internal arrangement of different parts of a computer is called the computer organization. It differs from one computer system to another. However, the basic organization remains the same for all types of computer systems.

              All computer systems perform the following five basic operations.

1. Inputting
2. Storing Processing
3. Outputting
4. Controlling

Computers receive most data from either the keyboard, scanner, mouse or disk. Information is saved on a floppy disk or hard disk. Data is manipulated or processed by the processors and the resulting output is either displayed on a monitor or printed on paper.

A block diagram of the basic computer organization is shown in figure 2.1. It depicts the five major building blocks, of functional units of a digital computer system. These five units correspond to the five basic operations performed by all computer system. The function of each of these units is described in subsequent sections.

CENTRAL PROCESSING UNIT (CPU):

The Central Processing Unit (CPU) is the brain of any computer system. In a human body, all major decisions are taken by the brain and all other parts of the body function as directed by the brain. Similarly, in a computer system, all major calculation, manipulations and comparisons are made by the CPU. The CPU is also responsible for activating and controlling the operations performed by all other unites of the computer system.

              The major pares of a CPU are:

(a)    Arithmetic and Logic unit (ALU)

(b)    Control unit (CU)

(c)     Main Memory of Primary Memory

Arithmetic and Logic unit (ALU):

All calculations are performed and all comparisons (dicisions) are made in the ALU. The data and instructions, stored on the primary memory prior to processing and manipulation of data is done in the Arithmetic and Logical Unit.

Intermediate results generated in the ALU are temporarily transferred back to the primary memory until needed again. After completions of processing, the final results available in the primary memory are sent to an output device. Such as monitor.

ALUs are designed to perform the four basic arithmetic operations- add, subtract, multiply, didide- and logic operations or comparisons such as less than, equal to, or greater than. Figure2.2 shows different operations of the computer system from the layman’s point of view.

In this figure, the calculator as a part of ALU represent the central processing Unit and the clock carries out the control function for different operations of the keyboard input and the monitor output. This figure gives more of a conceptual working of the digital computer. The actual block diagram representation, containing the jobs done by each part is shown in Figure 2.1.

Control unit:

How does the input device know that it is it is time for it to feet data into the storage unit? How dos the input device know that it is time for it to feed data into the storage unit? How does the ALU know what should be done with the data once the received? And how it is possible because of the control unit of the computer system. By selecting, instruction, the control unit is able to maintain order and direct the working of the entire computer system. Although it does not perform any processing on the data, the control unit acts as the central nervous system for all other components of the computer. It coordinates the entire computer system.