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Hard disks are available in a variety of sizes with storage capacities
as high as 5 TB (TeraByte) or even more. The CPU can access 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
Info Byte
First hard disk was introduced by Seagate in 1980 which could hold 5 MB data.
Optical Disc
An optical disc is an electronic data storage medium uses a low-powered laser beam to
read and write data.
Compact Disc (CD)
Compact Disc (CD) is an external storage device. It can hold up to 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
Types of CDs:
1. CD-ROM (Compact Disc Read-Only Memory): A CD-ROM is a CD containing data
that has been written at the time of manufacturing. The data 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 or erased.
3. CD-RW (Compact Disc Rewritable): A CD-RW can be used to write data again and
again. The data can be erased and modified as many times as required.
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 Blu-ray discs and DVDs is that
storage capacity of blue-ray disc is higher than that of a DVD.
Blu-ray disc
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Computers—Storage and Memory Device

