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.