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Hard Disk

The hard disk consists of one or more magnetic disks. Each disk in
the pack has top and bottom surfaces on which data is recorded
using magnetic head. It is permanently fixed in the system unit.
The most important function of the hard disk is to store program
files and data files.
Hard disk
Hard disks are available in a variety of sizes with storage capacities
as high as 5 TB (TeraByte) or even more. The CPU can accesses data
stored on a hard disk much faster than it can access data on a CD.

External hard disks are also available. They are the hard disks
that can be connected to any computer with the help of a USB port.
External hard disk

Tech Fact

First hard disk was introduced by Seagate in 1979 which could hold 5 MB data.

Optical Disc

An optical disc is an electronic data storage medium that can be used to write and read using a
low-powered laser beam.

Compact Disc (CD)
Compact Disc (CD) is an external storage device. It can hold upto 700 MB

of data. The CD drive reads information stored on a compact disc. CD drive
is usually connected inside the CPU box but can also be connected using a
USB port.
CD

Digital Versatile Disc or Digital Video Disc (DVD)

The DVD is almost similar to a CD, even the working is also similar. The only
difference is that it can hold more information than a CD. DVDs are widely
used for storing and viewing movies and other data.

DVD

Blu-ray Disc

Blu-ray disc is an optical disc. It is used for storing a large amount of
data. The main difference between DVDs and Blu-ray discs is that storage
capacity of blu-ray disc is higher than that of the DVD.

Blu-ray Disc

Computer System Organization - Hardware, Software & Memory 49