Storage devices can be classified as sequential access or direct access based on how data is accessed. Sequential access devices access data sequentially, like magnetic tapes, while direct access devices allow random access to data, like hard disks. Common storage devices include hard disks, CDs, USB drives, floppy disks, magnetic tapes, optical discs like CDs and DVDs, and solid state drives. Optical discs use lasers to read and write data in the form of pits and lands on a metal or plastic disc. Solid state drives have no moving parts and use flash memory for storage.

1. Storage devices

2. Storage devices
 storage device is also referred as digital storage , storage medium .
 a storage device is any hardware which is capable of carrying information ,
information can be permanently or temporarily for later use .
 Example :hard dick ,CD ,USB , floppy , etc.

3. Types of storage devices:
Storage devices are classified into two main categories , based on the access method:
1) Sequential access storage
2) Direct access storage
1) Sequential access storage
• a type of storage in which data is accessed sequentially one after the other is
called sequential access storage
• It is also known as serial access storage
• Slow process for accessing data
• The magnetic tapes and audio/video tapes are example of sequential access storage
device

4.  Direct access storage
• a type of storage in which data is accessed directly or randomly is called direct
access storage
• It is also known as random access storage
• It is fast process for accessing data
• Magnetic dick and optical disk flash memory are the example of direct access
storage device

5. Difference between sequential and random access storage
 Magnetic storage device
• Magnetic storage device is one of the most widely used secondary storage in
computer
• It consist of a magnetic medium on which information is stored
• Magnetic disk and magnetic tapes are the example of magnetic storage device

6.  Magnetic disk
• Magnetic disk are flat circular plates of metal or plastic , coated on both sides with
iron oxide
• Data is stored by magnetizing this film. The disk spins at high speed , and a magnetic
head mounted on a moving arm is used to read and write data.
o Advantages
 High capacity storage
 Inexpensive
 Data security
o Disadvantages
 Slower access speed
 Require maintenance

7.  Floppy disk
 A floppy disk is a portable magnetic storage media
 It is a plastic disk coated on both side with magnetic recording material
 It came in several sizes including 8-inch and 3.5-inch.
Advantages
• Small in size
• Easy to carry
• Used to transfer data from one computer to another.
Disadvantages
• small storage capacity
• Limited capacity

8.  Hard disk
 Magnetic storage medium for computer
 Hard disk are flat circular plates made of aluminum or glass and coated with a magnetic
material
 Data stored on their surfaces in concentric tracks
Advantages
• Larger storage capacity
• Have non-volatile memory
Disadvantages
• Slow at retrieving larger files
• Consume more power
 Zip disk
• Zip disk is a type of portable magnetic media
• Its storage capacity is up to 1000 MP
• It can be used to keep the back up of important data
• It is similar to a floppy disk but its storage capacity is about 100 times more than floppy disk

9.  Magnetic tape
 magnetic tape is a storage medium that allow for data collection and backup
 At first the tape were wound in wheel-reels, but then in cassettes came along
which offered more protection for the tape inside

10.  Optical storage devices
Today the most widely used storage device are optical storage devices.
 These devices use laser technology to store and read data to and from the optical disc.
 Optical disc
• An optical disc is a type of storage media that consist of a flat, round portable disc made of
metal .
• It is coated with a thin metal or plastic .
• The information on the optical disc is stored in the form of microscopic pits and lands .

11. Types of optical disc
Different types of optical storage disc are
• CD
• DVD
• Blue-ray discs
 CD
• CD stand for compact disc
• It was originally developed for sound recording but bow it is widely used for storing
computer data and programs
• Most widely used for storing huge amount of data
• Data store on the of spiral track in the form of lands and pits
 DVD
• DVD stand for digital video disc
• It is similar to a CD
• Data is also stored just like a CD on spiral track
• However , DVD has larger data storage capacity than CD

12.  Blue-ray disc
• blue- ray disc is a new type of optical storage device
• This storage device is reliable , faster, and has higher storage capacity than CD and
DVD
• The bumps on the blue-ray disc are smaller and very closely packed than DVD
 Solid state storage devices
• The solid-state storage device is also called a flash memory device
• It has no moving parts in it
• It contain a solid chip that can store data

13.  Types of flash memory devices
 Solid-state drives (SSDs)
 USB flash drives
 Memory cards
 Solid-state drive(SSD)
• SSD is a storage device that typically uses flash memory to store data
• It contain its own processor to manage its storage
• It has faster access time than traditional hard disk drives
Advantages
• It generate less heat
• Consume less power
• It is more reliable
Disadvantages
• It is more expensive than hard disk
• In case of SSD failure , recovery of data can be more difficult

14.  USB flash drive
• USB flash drive is also known as a pen drive
• It is flash memory device
• It is connected to a USB port in a computer or mobile device for writing and
reading data
• it is Small in size and light weight storage device
 Memory card
• A memory card is sometimes called a flash memory card or a storage card
• It is a small size removable flash memory device
• It is widely used in digital camera , mobile phones, video games etc.
• Todays, different types of flash memory cards are available . Some common types
of flash memory cards are compact flash, memory stick, microSDHC