Magnetic Tape and Optical Disk

2.3 Magnetic Tape

Magnetic tape is flexible plastic tape coated with magnetic material. It is widely used when large amount of data is to be processed sequentially. An advantage of magnetic tape is that it is very cheap and economical storage. Its major disadvantage is that it is very slow and it is only sequential.

There are two types of magnetic tape:

2.3.1 Cartridge Tape

Cartridge tape contains magnetic recording tape in a rectangular plastic box. On quarter-inch wide Cartridge is normally used with personal computers for backup. Another ½-inch tape is normally used with minicomputers and mainframe computers.

2.3.2 Reel-to-Reel Tape

Reel-to-reel tape consists of two reels. The supply reel is used to hold the tape during read and write operations. The take-up reel is used to hold the portions of the supply reel as it is being processed. When the tape moves from one reel to another, it passes over a read/write head to read or write data.

2.4 Optical Disk

Optical disk uses laser technology to read and write data. The LASER stands for Light Amplification through Stimulated Emission of Radiation. Laser beam writes on the surface by creating small pits (hole) in the disk.

Optical drive reads data by focusing laser beam on the surface of the disk. A laser detects the presence of a pit. The presence of pit indicates 1 and absence of pit indicates 0. Laser beams converts these pits into digital data.

The amount of space required to record an optical bit is much less than magnetic bit.

Optical disk storage capacity is from 650 MB to several GB.

The main categories of optical laser disks are CD and DVD.

2.4.1 CD

CD stands for compact disk. It is mainly used to store audio/video and computer software. The contents of CD can be read by CD drive. Different types of CDs are as follows:

1.  CD-ROM

CD-ROM stands for compact disk read-only memory. The data stored on CD-ROM can ony be read. It cannot be deleted or changed. CD-ROM is a portable storage device. Data can be transferred easily by using CD-ROM. It can store from 650 MB to 1 GB of data.

Uses of CD-ROM

·        CD-ROM is mostly used to store large amounts of information like sound, color graphics and videos.

·        It is often used to distribute new application software and games.

Advantages of CD-ROM

·         It is the least expensive way to store large amounts of data and information.

·         CD-ROM disks are durable and easy to handle.

·         Information can be stored on CD-ROM for many years.

Disadvantages of CD-ROM

·         The data cannot be edited.

·         It retrieves data and information more slowly than magnetic disks.

2.  CD-R

CD-R stands for CD recordable. The user can write data on CD-R only once but can read it many times. The data written to CD-R cannot be erased. CD-R drives are known as CD burners and are typically used to create custom music CDs. The process of putting information on CD is burning CD. CD-R is also known as WORM (Write Once Read many).

3.     CD-RW

CD-RW stands for compact disk rewritable. It is also known as erasable optical disk. The user can write data on CD-RW many times by erasing the existing contents. The most common type of erasable and rewritable optical disk is magneto-optical disk (MO). It uses the technologies of both magnetic disk and optical disk. Such disks are normally used for applications using large volumes of storage with little update activity.

2.4.2 Digital Video Disk (DVD) and Blu-ray Disk

DVD stands for Digital Video Disk. It is similar to CD-ROM. It uses a laser beam with short wave length. The short wave length reads smaller holes on the disk. Data storage capacity of the disk is increased if the hole size is small. So the storage capacity of DVD ROM is much greater than CD-ROM. It can store up to 17 GB of data.

·         DVD-R: DVD-R stands for digital video disk recordable. It is similar to CD-R discs. The user can write data on DVD-R only once but can read it many times. The data written to DVD-R cannot be erased.

·         DVD-RW: DVD-RW stands for digital video disk rewritable. The user can write data on CD-RW many times by erasing the existing contents.

·         Blu-Ray Disk: It is a new and more expensive DVD format. It provides higher capacity and better quality than standard DVDs especially for high-definition audio and video. It can store up to 100 GB of data.