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Hard Disk
The hard disk consists of one or more magnetic disks
called platters. Each disk in the pack has top and bottom
surfaces on which data is recorded using a magnetic head.
It is permanently fixed in the computer system. It is usually
used for permanent mass storage. The most important
function of the hard disk is to store program files and
Hard disk
data files.
The hard disk comes in a variety of sizes with different
storage capacities as high as 5 TB (TeraByte) or even more.
The CPU accesses data stored on a hard disk much faster
than it can access data on a CD.
External hard disks are also available. They can be
connected to any computer with the help of a USB port.
External hard disk
Clickipedia
The first hard disk was introduced by Seagate in 1980, which could hold 5 MB of data.
Optical Disc
An optical disc is an electronic data storage medium that can be written to and
read using a low-powered laser beam.
Compact Disc (CD)
The CD drive reads information stored on a compact disc
(CD). CD is an external storage device. The lifespan of an
optical disc is longer than a magnetic disk. It can hold up to
700 MB of data.
CD drive is usually connected inside the CPU box but can CD-Drive
also be connected using a USB port.
Types of CDs:
1. CD-ROM (Compact Disc Read-Only Memory): A CD-ROM is
a pre-recorded CD containing data or software that has been
written at the time of manufacturing. The data stored cannot be
modified or erased.
2. CD-R (Compact Disc Recordable): A CD-R can be used to
write data by the user only once. This data cannot be changed
CD
or erased later.
Computers—Storage and Memory Device 9

