4th Class

      Introduction   You may have used the computer to store games, music files and pictures in it. These files get stored in the memory devices. A memory device is a device that preserves information (data and instructions) for retrieval in the future. Every computer uses storage to hold software such as system software and application software. To boot up, a computer locates an operating system (system software) in the storage and loads it into memory. When users issue commands to start application software, such as word processing, the operating system locates the program in storage and loads it into memory. In this chapter, we will learn about some characteristics of memory devices.

      Secondary Memory Devices     All computers store and retrieve data. Since primary memory has a limited storage capacity and is not permanent, secondary storage devices are used to store large amount of data permanently. Secondary memory devices are external devices and stores data for the future. Secondary memory devices include magnetic disks like hard drives and floppy disks, optical disks such as CDs and CD-ROM and magnetic tapes, which were the first forms of secondary memory. Secondary memory (or secondary storage) is the slowest and cheapest form of memory. It cannot be processed directly by the CPU. It must first be copied into primary memory (also known as RAM). Secondary storage (or external memory) differs from primary storage because they are not directly accessible by the CPU. The computer usually uses its input/ output channels to access secondary storage and then more...

        Primary Memory or Main Memory                 Types of Main Memory:

• All computers have main or primary memory to store programs and data .while the computer is running.
• The main memory has 2 subtypes:RAM (Random Access Memory) and ROM (Read-only Memory).

      RAM (Random Access Memory) and ROM (Read-only Memory).     RAM (Random Access Memory)  RAM can be compared to a person's short-term memory and the hard disk to the long-term memory. The short-term memory focuses on work at hand, and can keep only a few facts in view at one time. If short-term memory fills up, your brain is sometimes able to refresh it from facts stored in long-term memory. more...

  Introduction     You can remember things because they are stored in your memory (brain). Similarly, a computer has memory to store data and information for future use. The Memory's the computer's work area. This is the place where the data and programs get stored before being processed and the place where the results get stored before being sent as output. Suppose you are asked when your birthday is or the name of your friends, you will reply immediately because you 'member them and this information s already in your memory. A computer also has a memory which stores a lot of information inside it. A computer stores everything in its memory. All the data that enters into the computers first get converted into the binary number system. One digit in binary number system is called bit and combination of eight:  is called byte. more...

         Scanner     A scanner creates an electronic form of the printed image which can then be manipulated, changed and modified according to the requirements. The scanners can convert any image and printed text into electronic form by shining light on to the image and sensing the intensity of the reflection at every point. The resolution of a scanner is a measure of the number of pixels it uses. Higher resolution means clearer pictures. Scanners come in 2 different models - Hand-held Scanner and Flatbed Scanner           Hand-held Scanner     Hand-held scanner is a small handheld scanning device used for digitizing images. While images from a handheld scanner are considered low quality, today's technology enables full colour24 bit scanning. Depending on the scanner device type and manufacturer, handheld scanners can also more...

      Speakers     The speakers that are attached to the computer are similar to the ones that are connected to a stereo. The computer system's speakers are smaller and they contain their own small amplifier. Speakers receive the sound in the form of electric current from the sound card and then convert it into sound format. Computer speakers range widely in quality and in price. The computer speakers typically packaged with computer systems are small plastic boxes with mediocre sound quality. Some of the slightly better computer speakers have equalization features such as bass and treble controls which improves their sound quality. The internal amplifiers require an external power source, known as a 'wall-wart'. Laptops come with integrated speakers.             more...

         Modem     A modem is a device attached to the computers that can convert digital signals to analog signal and vice- versa. Digital signal is a group of discrete electronic units that are transmitted in rapid succession and an analog signal consists of continuous electrical waves. Modem is a short name for modulator-demodulator, where modulator can convert digital signals to analog signals and demodulator does the opposite. Modem is a device that enables computers, fax machines and other equipment to communicate with each other across telephone lines or over cable television network cables. Since telephone cables can carry analog signals, the computer generated digital signal is first converted into analog form so that it can be carried by telephone lines. Upon receiving it, the modem at receiver end can understand it. Modems transmit data at different speeds, measured by the more...

        Microphone       You can send sound or audio input to the computer through a special input device called microphone. A microphone converts the sound received into the computer's format, which is called digitized sound or digital audio. A microphone can work only if your computer has a special hardware known as sound card. Sound is more often used in multimedia where there is recorded narration, music or sound effects. A microphone is a hardware peripheral that is a popular solution for computer gaming.   In 1876, Emile Berliner invented the first microphone used as a telephone voice transmitter. Microphones are used in many applications such as telephones, tape recorders, karaoke systems, hearing aids, motion picture production, live and recorded audio engineering, megaphones, in radio and television broadcasting and in computers for recording voice and speech recognition. Richard and Morton more...

       CD-ROM     You must have seen or used CDs for watching movies, playing games and listening to music. CD-ROM is an acronym of "Compact Disc Read-Only Memory". It is a type of optical disk capable of storing large amounts of information. Users use CD-ROMs to record information including text, graphics or audio on the CD, CD-ROMs are stamped by the vendor and once stamped; they cannot be erased and filled with new data. To read a CD, you need a CD-ROM player. CD-ROMs are particularly well-suited for information that requires large storage capacity. This includes large software applications that support colour, graphics, sound and especially video.              Given below is the information about CD-ROM. Select the correct statements. 1. CD-ROM is an acronym more...

     Printer     Printers are output devices used to produce printed papers from the computer, Printers can produce text and images on paper and this is called 'hard copy'. Based on the technology used, they can be classified as Impact or Non-impact printers. Impact printers use the typewriting printing mechanism where there is a mechanical contact between the print head and paper. Dot-matrix and Character printers fall under this category. Non-impact printers do not touch the paper while printing. They use chemical, heat or electrical signals to etch the symbols on paper. Inkjet, DeskJet, Laser and Thermal printers fall under this category of printers. Printers are generally slow devices (30 pages per minute are considered fast) and the cost per page is actually relatively high.           more...