1. Memory Random Access Memory (RAM) and Read Only Memory (ROM)

2. Random Access Memory (RAM) RAM is a type of memory that can be read from or written to. This is therefore a read/write random access memory. This memory stores the input data and the program that users give to the computer for immediate execution. RAM is volatile, meaning that it loses its contents when the power is shut off. Random access means that the storage cells of a RAM memory are organised so that the access time of any cell is the same for all.

3. Read Only Memory (ROM) ROM is a type of memory that can be read from but cannot be written to. ROM is non-volatile, meaning that it retains its contents even when the power is shut off. These programs are written permanently into the memory during manufacture. Such programs are called the firmware.

4. Read Only Memory (ROM) contd.. Programmable ROM (PROM) Erasable PROM (EPROM) Electrically alterable ROM (EAROM)

5. Read Only Memory (ROM) contd.. PROM This is a type of ROM that may be customised to the needs of the users. That is, data and programs can be written in it after manufacture but once written, it becomes permanently fixed. EPROM This is a type of ROM that may be reused. That is, the contents of EPROMs may be erased by a special process and then reprogrammed/rewritten again by the user.

6. Read Only Memory (ROM) contd.. EAROM This a state-of-the-art ROM chip that may be erased and reprogrammed using an electrical signal to change the bit pattern of the program. Cache memory – very high speed memory built into the processor to enhance the processor speed. Data that are most likely to be needed next by the CPU are kept in this memory. Cache memory is usually in the range of 512 KB of storage.

7. INPUT DEVICES Keyboard Optical Character Reader (OCR) – used to read any printed text. They can interpret handmade marks, handwritten characters, machine printed characters and special symbols and codes. – Optical Character Readers scan the text optically, character by character, convert them into machine readable codes and store the text in the system's storage medium.

8. Optical Character Reader (OCR) contd… OCR devices are expensive and are used only when there are large quantities of documents to be keyed in Advantages – It can be used to reformat printed or typed documents by inputting through the reader and outputting on the systems printer. – It can be used to consolidate texts from various documents into one document. – It can serve as a link between the word processing system and the conventional typewriter

9. Magnetic Ink Character Recogniser (MICR) It is a device that can identify characters printed with ink that contain particles of magnetic material. MICR is used mainly in the banking industry to read cheques. Since the MICR system can recognise only certain character styles, the characters have to be accurately formed

10. Mark Sense Reader (MSR) also known as optical mark reader (OMR) can recognise marks made by a pencil or pen on a specially designed card These cards and forms are pre-printed for special purposes so that a mark in a particular position may represent certain meaning. Such forms are used in processing selection tests, survey questionnaires, and the like, where answers are recorded as dark pencil marks in certain boxes.

11. Graphics Tablet Graphics tablet is a computer-based terminal with additional features for creating, storing and printing pictures create an image of a picture by simply moving a stylus on the picture. As the stylus moves the picture is created on the screen for checking. The picture can be stored or printed out on a plotter.

12. Mouse used to position the cursor on the screen Its manipulation on a flat surface moves the cursor in the same direction as the movement of the mouse. The box contains a ball underneath which senses the movement and transmits it to the computer over the cord.

13. Trackball A trackball is a pointing device that works like an upside-down mouse. It consists of an exposed ball which can be rolled with the help of our thumb to move the cursor around the screen. Trackballs are popular with the notebook computers.

14. Touch Screen The monitor screen can be designed to be touch-sensitive so that we can input instructions by merely touching on-screen prompts. Such screens are especially helpful when people are unfamiliar with computers.

15. Light Pen A light pen is a handheld, light-sensitive stylus attached to a computer that accepts the stylus position on the monitor as an input. can move the pen across the screen to make menu selections or draw curves.

16. Bar Code Reader Bar code is a special bar chart created on products to represent product number, cost and other details. When a bar code is scanned, the bit patterns represented by the marked bars are translated into meaningful information. Bar codes are extensively used in libraries, departmental stores, post offices, inventory and sales departments.

17. Sensors In many scientific applications, data input is done through a sensor. These devices allow direct input of physical data to a computer for analysis. This method provides a timely and accurate data acquisition.

18. Digital Camera A digital camera can capture a scene, digitise the image and store the digitised image on a small disk within the camera. The disk can be removed and read by a computer.

19. Voice Recognition Voice-recognition devices are available that can be used to provide voice input directly to a computer. The computer recognises the spoken words and converts them to output, either in audio form or in printed form. Since these devices understand a limited vocabulary, they are not widely used at present.