EXTERNAL STORAGE

A computer’s primary storage or main memory is volatile. This means that the content in memory will be lost when the computer is turned off. Therefore, a permsnent storage area is required to store data and programs that are not needed immediately by the computer. This kind of storage is called the secondary or external storage.

Data stored in a secondary storeage medium is intended to be permanent. Secondary storeage media are inexpensive and have a large capacity to store programs and user data.

Just as you need an audio palyer to listen to an audio cassette,you need a storage device called a drive to write to and read from a storage medium.

Some of the commonly used external storage devices are :

1.Hard disk drives

2.Floppy disk drives

3.Compact disk- Read Only Memory (CD-ROM) 

   drives and CD writers

4.Dgital Video Disk (DVD) drives and DVD

   writers

Hard Disk Drive

A hard disk drive is avery typical exyernal storage device found in almost any PC. The hard disk drive is attached to the system unit from within, but it is possible to remove a hard disk drivefrom a computer if necessary. The storage capacity of hard disks varies up to a capacity of terabytes. Student PCs typically have a capacity of less than 80 gigabytes.

Floppy Disk Drive

The floppy disk drive is an external storage device used to read from and write to a floppy disk.

A floppy disk is a portable storeage medium that can store a small amount of data. The storage capacity of a floppy disk a usually 1.44MB. One disadvantage of a floppy disk is that it is prone to damage by heat, dust and magnetic fields. Example,a simple magntic paper clip may destroy data stored on a floppy disk. For this reason, you should save student records and other important data either on multiple floppy disks or an alternative medium, such as a compact disk. A floppy disk is also called a floppy or diskette.

Compact Disk—Read Only Memory (CD-ROM) Drive

The CD-ROM drive is an external storage device used to read from a CD-ROM. The storage capacity of most CD-ROMs is approximately 650 MB or 700 MB, which is also the reason why large software programs usually come with an installation CD-ROM. The advantage of a CD-ROM is that the datastored on it is less prone to damage because the data present on a CD-ROM cannot be changed.

Rewritable CDs and CD writers

A CD writer is astorage device that can write data to a rewritable CD, which is a special type of CD that allows you to erase the content already stored and store data again. CD-writers are capable of storing a large amount of data on a CD. They are also capable of reading CD-ROMs. Keep in mind that CD-ROMs and rewritable CDs are different media types, they only look the same. People tend to call both CDs.

Digital Video Disk (DVD) Drive

A DVD drive is an external  storage device used to read from a DVD_ROM, although DVD drives are also able to read CDs. A DVD_ROM is similar to a CD-ROM, except that it can store lager amounts of data. DVDs that can store up to 17 GBs are also available. Because of their capacity, DVDs are generally used to stored very large multimedia presentations and movies that combine high quality sound and graphics.

 Comparing Externel Storage Types

A comparison of floppy disks, hard disks, CD-ROMs and DVDs.

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Proessing Devices (System Unit)

when you have a conversation with a friend,your ear acts as the input device. It receives the information your friend gives you and passes on yhe information to your brain. Your brainacts as the processing device. It understands the information and frames an appropriate response. The mouth acts as the output device and gives a reply to your friend.

Similarly, in a computer,device, such as the keyboard and the mouse are input devices. The box-like structure called the system unit is responsible for all the processing required  to convert the input to the required output. Devices ,such as the monitor and the printer are output devices. These input and output devices attached to your computer need to conncet to a component within your system unit to allow data to flow. For exemple, the monitor is connected to a video card and the speakers to a sound card. The video card and the the sound card, in turn, reside on the motherboard tofether with the processor, memory and optional internal I/O devices, such as a network interface card.

Motherboard

The system unit contains a large board that has anumber of tiny electronic circuits and other components. It is known as the motherboard. The motherboard is a very important part of the system unit and houses several vital compenents of the computer.

The microprocessor is the the most important component of the motherboard. Data is recived from the input devices. The actual processing of data, that is the arithmetic or logical operations on the giver data,occurs in the microprocessor. Finally, the processed information is the output devices depicts the working of a computer.

Video Card

A video card plugs into a personal computer to give it display capabilities. In other words, it enables your computer to represent data in a visual form. Video cards are also called video adapters, video boards, video display boards, graphics cards and graphics adapters. Each adapter provides digital-to-analog conversion, video RAM and a vider controller so that can be sent to a computer’s display.

Sound card

A sound card is a device in the system unit that enables a computer to accept, process and play sound, A sound card enabl4es the computer to record sound through a microphone. Manipulate sound stored on a disk and output the sound through speakers.

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Storage

Computer storage refers to the data stored in an electromagnetic form to be used by the processor. You can measure the amount of data stored on a computer just as you can measure the amount of ater in container, although measurement units are different, of course. The storage capacity defines the amount of data that can be stored on a storage device.

Computer Data

A computer stores a variety of data and information in its memory,including numbers (0-9), letters (A-Z) and symbols and other characters (#,{},. ‘ ~ ^). A computer uses the binary system to represent these characters. In a binary system, only two digits, 0 and 1, are used. The 0s and 1s in the binary system are known as bits (binary digits). A bit is the smallest unit of measurement of storage capacity. A set of eight bits is called a byte.

NOTE

Kilobytes, megabytes, gigabytes, terabytes are higher  units for mrasureing the capacity of a storage of a storage device.

8 bits                             = 1 byte

1024 bytes                    = 1 kilobyte(KB)

1024 KB                       = 1 megabyte (MB)

1024 MB                      = 1 gigabyte (GB)

 

1024 GB                       = 1 terabyte (TB)

Internet S

torage

Computers use two types of storage: external storage and internal storage. External storage is explained in the  next section. The internal  storage, also called primary storage is the main memory. It stores data and instructions for processing .it also stores the output data temporarily before it is sent to an appropriate output device. The act of retrieving existintg data from memory is called reading out or simiply reading. The process of storing data in memory is called reading  in or writing.

There are two types of internet storage:

1. Random Access Memory (RAM)

2. Read Only Memory (ROM).

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Input/Output devices

There are devices that perform the activities of an input devices in addtition to those of an output device. Such devices are called input/output devices or I/O devices.Modems and network interface cards are examples of input/output devices.

Modem

The term modem stands for modulator-demodulator. Data can be transmitted over different media, such as telephone cables and terrestrial transmission. Telephone cables cab carry waveform called analog signals, analog signals are prone to disturbances from noise and magetic pilses. A relativerly new form of transmission called digital uses binary format (an encoding/decoding system based on 0s and 1s) to send and receive data. This is the format used by computers to send and receive. However, digital signals to cannot be sent through telephone lines. Hence, there is a need to convert the digital signals to analog signals before they are transmitted through telephone cables. Similary, the transmitted data has to be converted to digital signals at the receiving end. A modem is an electronic device used to perform the function of converting the digital signals to analog signals and vice versa.

When you send a massage from  your computer to another computer, the modem acts as an output device. However,when your computer receives a message, the modem acts as an input device. A modem  can be external or internal to the system unit. Modems that are connected to the system unit through cables are called external modems.

Modems are also available as part of system unit. Modems that are built-in to the system unit are called internal modems.

Network interface card

A network interface card (NIC) is a card that is installed in a computer so that it can be connected to a network. Network interface cards provide a dedicated, full-time connection to other computers, for example in a classroom.most network interface cards are designed for a particular type network,although some can serve multiple networks.in classrooms,thmost typical network is Ethernet. Ethernet is a network standard of computer communication using either coaxial or twisted pair cable. Other standards include Tokenring and Framerelay, but these are  less common in classroom environments.

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Output Devices

Any device that is capable of representing informationin a computer is called output device.There are three important output devices connected to the system unit.
 §      Monitor §      Printer
 §      Speakers



Monitor
A monitor resembles a television screen, only with a much higher resolution for better display quality. It is used to display information from the computer. The monitor display text grephics. It typically comes with its own separate power button to turn it on or off.
Printer
A printer is used to transfer data from a computer onto paper. There are colour printers well as grayscale printers available on the market. The fdifferent types of printers are dot matrix printers, inkjet printers and laser printers.
Speakers
Speakers are used to play sound. They may be built in or externally connected to your system. Speakers allow you listen to music and hear sound effects spoken text using your computer. Suppose you want to give a lesson to a group a visually impaired students, you can multimedia presentation. To make the lesson more accessible to these students, you can structure the lesson around an audio componet, thus allowing the students to participate in the lesson using sound rather than relying on the screen presentation.

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