In addition to magnetic storage, there is also optical storage.

Optical disk: A storage device that uses reflecting surfaces and laser technology to read and write data on a disk. Also known as a laser disk.

With optical storage, data is burned into the storage medium using beams of laser light. The burns form patterns of small pits in the disk surface to represent data. The pits on optical media are permanent, so the data cannot be changed. Optical media are very durable, but they do not provide the flexibility of magnetic media for changing the data once they are stored.

There are three types of optical disks.

• CD-ROM’s are the most popular type of optical storage. CD-ROM stands for Compact Disc Read Only Memory. A computer CD-ROM disk, like its audio counterpart, contains data that has been stamped on the disk surface as a series of pits. To read the data on a CD-ROM an optical read head distinguishes the patterns of pits that represent bytes. CD-ROM disks provide tremendous storage capacity. CD-ROMs usually come with data already written onto them. These days most applications software is provided on CD-ROM.

• It is now possible for computer users to write data to an optical disk. These are known as WORM disks, which stands for ‘Write Once Read Many’. A single CD holds up to 680 megabytes, equivalent to over 300,000 pages of text in character format, and these disks are quite durable. These CDs are know as CD re-recordable (CD-R). There are other types of WORM disks, although there is no standard for these.

• There is a third type of optical disk which can be erased and use to rewrite new information. These are sometimes known as EO (erasable optical) disks and CD-RW (CD rewritable).

Magneto-optical disks combine magnetic disk and CD-ROM technologies. Like magnetic media they can read and written to and like floppy disks they are removable. They can store over 200 MB of data, and speed of access to this data is faster than a floppy but slower than a hard drive. There is no universal standard for these yet. CD-ROMs and magnet-optical disks are very useful for storing images. These take up much more storage space than data in character format, such as in word-processed files.

The importance of documentation

The computer hardware, software and peripherals will be accompanied by documentation, which explains how the various systems or programs operate.

Documentation: Information needed to develop, use or maintain computer hardware and software and to permit access and retrieval of the data.

Although documentation usually comes in the form of printed manuals, guide books, it may also come in electronic form, such as in ‘help screens’ contained within the computer software or documentation in data dictionaries and so on. Often, documentation is created when a specific computer application is used. For example, if a government office creates a data base of employees in order to administer payroll, documentation may be created describing how the database was established, what it is to be used for and what data fields have been created. This documentation can be critical to understanding the database system, particularly if it is being managed in an archival environment long after the creators of the system have left.

Documentation should always be retained.

Disposing of documentation can cause problems in the future, particularly if you have to reload software from the beginning. Documentation can also contain licences for the legitimate use of the software. Therefore it is critical to protect documentation and ensure it is readily available.