Archive for Components

Memory Unit

There are two kinds of computer memory: primary and secondary. Primary memory is accessible directly by the processing unit. RAM is an example of primary memory. As soon as the computer is switched off, the contents of the primary memory is lost. You can store and retrieve data much faster with primary memory compared to secondary memory. Secondary memory such as floppy disk, magnetic disk, etc., is located outside the computer. Primary memory is more expensive than secondary memory. Computer memory is used to store two things: i) instructions to execute a program and ii) data. When the computer is doing any job, the data that have to be processed are stored in the primary memory. This data may come from an input device like keyboard or from a secondary storage device like a floppy disk.As program or the set of instructions is kept in primary memory, the computer is able to follow instantly the set of instructions. For example, when you book ticket from railway reservation counter, the computer has to follow the same steps : take the request, check the availability of seats, calculate fare, wait for money to be paid, store the reservation and get the ticket printed out. The program containing these steps is kept in memory of the computer and is followed for each request. But inside the computer, the steps followed are quite different from what we see on the monitor or screen. In computer’s memory both programs and data are stored in the binary form. You have already been introduced with decimal number system, that is the numbers 1 to 9 and 0.

The binary system has only two values 0 and 1. These are called bits. As human beings we all understand decimal system but the computer can only understand binary system. It is because a large number of integrated circuits inside the computer can be considered as switches, which can be made ON, or OFF. If a switch is ON it is considered 1 and if it is OFF it is 0. A number of switches in different states will give you a message like this: 110101……10. So the computer takes input in the form of 0 and 1 and gives output in the same form, i.e., 0 and 1 only. Is it not absurd if the computer gives outputs as 0’s & 1’s only? But you do not have to worry about. Every number in binary system can be converted to decimal system and vice versa; for example, 1010 meaning decimal 10. Therefore, it is the computer that takes information or data in decimal form from you, converts it into binary form, processes it producing output in binary form and finally again converts the output to decimal form.
The primary memory as you know in the computer is in the form of IC’s (Integrated Circuits). These circuits are called Random Access Memory (RAM). Each of RAM’s location stores one byte of information. (One byte is equal to 8 bits). A bit is an acronym for binary digit, which stands for one binary piece of information. This can be either 0 or 1. You will know more about RAM later. The Primary or internal storage unit is made up of several small storage locations called cells. Each of these cells can store a fixed number of bits called word length.
Each cell has a unique number assigned to it called the address of the cell and it is used to identify the cells. The address starts at 0 and goes up to (N-1). You should know that the memory is like a large cabinet  containing as many drawers as there are addresses son memory. Each drawer contains a word and the address is written on outside of the drawer.

Input Devices

An input device presents data to the processing unit in a machine-readable form. Although the keyboard is a common input device for a small computer, a system may also support various other input devices such as Optical Character Recognition (OCR), Magnetic Ink Character Recognition (MICR), mark sense reader, etc.

1 Key board
The keyboard is very much like a standard typewriter keyboard with a few additional keys. The basic QWERTY layout of characters is maintained to make it easy for the trained typist to use the system. The additional keys are included to perform certain special functions such as loading a program, edition a text, etc. These are known as function keys that vary in number from system to system.

2 Optical Character Recognition
Often abbreviated as OCR, optical character recognition involves reading text from paper and translating the images into a form that the computer can manipulate. An OCR system enables you to take a book or a magazine article and feed it directly into an electronic computer file.

3 Magnetic Ink Character Recognition (MICR)
An MICR can identify characters printed with a special ink that contain particles of magnetic material. This device particularly finds applications in banking industry. Since the MICR system can recognise only certain character styles, the characters have to be accurately formed.

4 Optical Mark Recognition (OMR)
Optical mark recognition, also called mark sense reader, is a technology where an OMR device senses the presence or absence of a mark, such as pencil mark. OMR is widely used in tests such as aptitude tests.

5 Bar Code Reader
These devices are generally available in super markets, bookshops, etc. Bar-code readers are photoelectric scanners that read the bar codes or vertical zebra striped marks, printed on product containers. Supermarkets use a bar code system called the Universal Product Code (UPC). The bar code identifies the product to the
supermarket’s computer which has a description and the latest price of the product. The computer automatically tells the Point of Sales (POS) terminal what the price is.

6 Digitiging Tablet
This is an input device that enables you to enter drawings and sketches into a computer. A digitiging tablet consists of an electronic tablet and a cursor or pen. A cursor (also called a puck) is similar to a mouse, except that it has a window with cross hairs for pinpoint placement, and it can have as many as 16 buttons. A pen (also called a stylus) looks like a simple ballpoint pen but uses an electronic head instead of ink. The tablet contains electronic field that enables it to detect movement of the cursor or pen and translate the movements into digital signals that it sends to the computer. Digitiging tables are also called digitizers, graphics tables, touch tables or simply tables.

7 Scanner
Scanner is an input device that can read text or illustrations printed on paper and translate the information into a form that the computer can use. A scanner works by digitizing an image – dividing it into a grid of boxes and representing each box with either a zero or a one, depending on whether the box is filled in. The resulting matrix of bits, called a bit map, can then be stored in a file, displayed on a screen and manipulated by programs. Optical scanners do not distinguish text from illustrations, they represent all images as bit maps. Therefore, you cannot directly edit text that has been scanned. To edit text read by an optical scanner, you need an optical character recognition (OCR) system to translate the image into ASCII characters. Most optical scanners sold today come with OCR packages.

8 Mouse
Mouse is a device that controls the movement of the cursor or pointer on a display screen. It is a small object you can roll along a hard and flat surface. As you move the mouse, the pointer on the display screen moves in the same direction. Mouse contains at least one button and sometimes as many as three, which have different functions depending on what program is running.

9 Light Pen
Light pen is an input device that utilizes a light-sensitive detector to select objects on a display screen.

10 Speech input devices
Speech or voice input devices convert a person’s speech into digital form. These input devices, when combined with appropriate software, form voice recognition systems. These systems enable users to operate microcomputers using voice commands.