Storage Devices

Storage devices save computer files on storage media, objects that can hold digital data. All programs and data are stored in files – each accessible to the computer by its file name. There are different types of files for different types of information. For example, a user might store a business letter as a text file and a photograph as a graphics file. A photograph takes much more storage space than text does.

Storage devices include hard drives, floppy drives, CD drives, DVD drives, and tape drives. All these devices can also serve as input and output devices.

Hard drives contain one or more hard disks – magnetic disks that hold data. Data are stored on tracks and a hard disk has thousands of tracks. It also has the read/write heads that move in and out to specific tracks to store or to call up data for the computer to use. Hard drives also have cables and other hardware for transferring data to and from the computer.

CD-ROM drives read data from CD-ROMs, the most common means of distributing software to PCs. A standard CD-ROM can store about 650 megabytes, roughly equivalent to 250, 000 pages of double-spaced typewritten text. CD-ROMs are a popular means for distributing multimedia programs. Such programs combine several forms of information – text, illustration, animation and sound.

DVD-ROM drives read DVDs, discs that are the same size as CD-ROMs but hold much more information. A DVD stores data on one or both sides. A single DVD can store up to 17 gigabytes of data. DVD-ROM drives can also read CD-ROMs.

Floppy drives store data on floppy disks – small, flexible magnetic disks encased in hard plastic shells that can be inserted into and removed from the drive. Floppy disks are used to store information for later use by the same computer, and to move information from one computer to another. Typical floppy disks can store from 1 to 2 megabytes of data.

Removable storage drives store data on high-capacity disks or cards. Computer operators use them to expand storage capacity beyond what is available on the hard drive, to store data for transport between computers, and to back up large amounts of information stored on hard disks. If the hard disks were to fail or become damaged, an operator could restore the information by copying it from the removable disks or cards.

Some removable storage drives are essentially hard drives without permanently mounted disks. Disks encased in special cartridges can be inserted into and removed from these drives.

Other types of devices that store data on removable discs include CD-R and CD-RW drives. These drives record data on two special kinds of compact discs. A CD-R (Compact Disc – Recordable) can be recorded only once, and the data on it cannot then be changed or erased. A CD-RW (Compact Disc – Rewritable) can be recorded over and over again, and data can be erased or changed. CD-R and CD-RW drives can read virtually all other types of CDs. Most ordinary CD-ROM drives can read a CD-R. Modern, highly sensitive CD-ROM drives can read CD-RWs. Like CD-ROMs, CD-Rs and CD-RWs can store up to 650 megabytes of data. A smaller type of CD-R, about two-thirds the diameter of a regular CD-R, can store up to 185 megabytes of data. Some digital cameras record images on these discs.

Some removable storage devices use memory cards that store data using memory chips. Most cards store up to 1 gigabyte of data.

Tape drives store data on magnetic tape in much the same way as audiotape recorders store sound information. They copy data much more slowly than disk drives. The main use of tape drives is to back up information stored on hard dicks.

Exercise 1. Study this information about storage devices. Then complete the blanks in the