Secondary storage devices

1. Introduction to Computer
Lecture # 10
Course Instructor : Sehrish Rafiq
Govt. Girls Degree College Maneri Swabi
Higher Education Department KP

2. Lecture Overview
• Secondary Storage Devices
Magnetic Storage Devices
Magnetic Tapes
Hard Disks
Floppy Disks
Zip Disks
Optical Storage devices
Compact Discs
Digital Versatile Discs
Blu-ray Discs
Flash Drives

3. Secondary Memory/ Storage
• Secondary memory/storage is also known as auxiliary memory/storage.
• Secondary memory devices are those memory devices which are not
directly accessible by the CPU.
• To process data and programs stored on secondary storage must first be
brought in to primary memory for processing.
• Secondary storage devices are non-volatile and they provide permanent
storage to data.
• Secondary storage devices can store huge amount of data and for long
term.
• These devices can store data and programs permanently and for long term.
• Examples:-
Magnetic Storage Devices
Optical Storage devices
Flash Drives

4. Magnetic Storage Devices
• Magnetic storage media and devices store data in the form of tiny magnetized
spots.
• These devices are coated with magnetic material such as iron oxide or ferric
oxide to store binary data.
• Stored data can be read and erased using tiny electromagnets.
• Magnetic storage is a form of non-volatile storage.
• This means that the data is not lost when the storage device is not powered.
• There are three types of magnetic storage devices :-
Magnetic Tapes
Hard Disks
Floppy Disks
Zip Disks

5. Magnetic Tapes
• A magnetic tape is a long and narrow strip of plastic on which data is stored
in the form of magnetized spots.
• At first, the tapes were wound in wheel-like reels, but then cassettes and
cartridges came along, which offered more protection for the tape inside.
• One side of the tape is coated with a magnetic material.
• Data on the tape is written and read sequentially.
• Finding a specific record takes time, because the machine has to read every
record in front of it.

6. Continued…
• Most tapes are used for archival purposes, rather than ad-hoc
writing/reading.
• A device that stores and reads computer data on magnetic tape is called
a tape drive, a tape unit, or a streamer.
• Data is written into 'tracks' on the medium.
• Older magnetic tapes used 8 tracks, while more modern ones can
handle 128 or more tracks.

7. Magnetic Tapes

8. Hard Disk
• A hard disk drive (HDD) is a non-volatile computer storage device containing
magnetic disks or platters rotating at high speeds.
• These disks or platters are made of rigid aluminum or glass.
• A hard disk also contains a mechanical arm containing read/write heads
known as actuator arm.
• When the platters rotate, the actuator arm can write new data on them and
can read the existing data from them.
• Hard disk is an essential part of digital computers nowadays and is used to
store huge amount of data permanently.
• A hard disk drive is also known as a hard drive.
• The storage capacity of hard disks nowadays is in terabytes.

9. Hard Disk

10. Hard Disk

11. Floppy Disks
•Floppy disks are thin removable diskettes made of flexible plastic.
•These disks are coated with magnetic material such as iron oxide.
•By the help of particles of this material computer data and programs are stored
on them.
•Typically they are 3.5" in diameter and capable of storing up to 2 MB of data.
•These diskettes are enclosed inside square shaped plastic casing.
•Data on floppy disk can be written/read by the help of a Floppy Disk Drive.

12. Floppy Disks
• They are portable and were used to transfer data from one computer to
another computer.
• Nowadays people use USB’s instead of floppy disks.

13. Zip Disks
• A Zip disk was an advanced version of the floppy disk.
• They look similar to floppy disks, but are slightly larger and thicker, and have
stronger plastic casing which makes them easier to store and handle.
• The magnetic coating used in Zip disks is of higher quality than that used in
floppy disks, and they could store more data than floppy disks.
• Like floppy disks, Zip disks are lightweight and portable.
• The disk needed a special drive called the Zip drive in order to be used.
• Zip disks are available in 100-250-MB capacities and are used to store, share
and back up large amounts of data, which was not possible with ordinary
floppy disks.

14. Zip Disks

15. Optical Storage Devices
• Optical storage devices use optical storage techniques and
technology to read and write data.
• It is a computer storage disk that stores digital data in the form of
slightly burnt spots.
• They use laser beams to read and write data.
• They are non-volatile and can store more data than magnetic tapes
and floppies.

16. Optical Storage Devices
• There are three types of optical storage devices.
 Compact Discs
 Digital Versatile Discs
 Blu-ray Discs

17. Compact Disc
• Compact Discs are often abbreviated as CD’s.
• They are also known as CD-ROMs, or Compact Disc - Read Only Memory.
• They are small circular plastic disks having a shining surface.
• They store and retrieve computer data or music using light.
• Compact Discs are faster and could hold more information than floppy
disks.
• CDs can hold up to 700 MB of data, which is about 80 minutes of music.
• The diameter of a normal CD is 120 mm.

18. Digital Versatile Disc
• Digital Versatile Disc abbreviated as DVD is an optical storage device like
Compact Disc.
• Physically, a DVD and CD look the same.
• Both are of the same size and typically have one side with a label and the
other side that the laser reads, unless it is a double-sided DVD.
• However, DVD’s store data in compressed form which allows them to hold
more data than a CD.

19. Blu-ray Disk
• A Blu-ray disk (BD) is a high-capacity optical disk medium.
• It can store large amounts of data and was designed to supersede the
DVD.
• Blu-ray technology gets its name from the blue-violet laser that is used to
read Blu-ray disks.
• Compared to a DVD’s red laser, a blue laser permits more information to
be stored at a greater density.

20. Flash Drives
• A flash drive is a small, portable storage device.
• They are often referred to as pen drives, thumb drives, or jump drives.
• The terms USB drive and solid state drive (SSD) are also sometimes used.
• Most flash drives have a storage capacity from 2 GB to 64 GB.
• Flash drives can be written and rewritten to an almost unlimited number of
times, similar to hard drives.

21. Flash Drives
• Flash drives have completely replaced floppy drives for portable storage
and, considering how large and inexpensive flash drives have become,
they've even nearly replaced CD, DVD, and BD disc for data storage
purposes.