Chapter 2 part 2

Storage devices
• Storage device : stores data and
programs permanently its retained after
the power is turned off.
• The most common type of storage device
is hard drive.
• All information on computers are stored in
• The computer store data in the form of bytes
(8-bit) a storage medium can hold a number of
Bytes .
• A byte is approximately one character ( letter
‘a’, number ‘1’ , symbol ‘?’ etc…).
Units of Measurements
1- Bit : the smallest unit. It holds a single value, ether
1’s or 0’s .
2- Byte : A byte consist of 8 bits.[Byte=8bits]
3- Kilobyte : consist of 1024 bytes.[KM=1024bytes].
4- Megabyte : consist of 1024 KM.[MB=1024KM].
5- Gigabyte : consist of 1024 MB.[GB=1024 MB].
6- Terabyte : consist of 1024 GB.[TB=1024GB].
TYPES OF Storage
Primary storage
(Internal storage)
Secondary storage
(External storage)
• Primary storage
– Volatile storage(changeful)
– Temporary storage
• Secondary storage
– Nonvolatile storage
– Permanent storage
Secondary Storage
• Secondary storage permanently saves information for future
use; to share information with others; to modify at later date.
• Secondary storage is nonvolatile – stores programs and data
as opposed to temporary storage (RAM).
• Characteristics include:
• Media or medium – actual physical materials that holds the data
and programs.
• Capacity – measures how much a particular storage medium can
• Storage devices – hardware that reads data and programs from
storage media (most also write to storage media).
• Access speed or access time – measures the amount of time
required by the storage device to retrieve data and program.
Secondary Storage
• Writing – process of saving information to the
secondary storage device.
• Reading – process of accessing information from
secondary storage.
Secondary Storage Devices
- Examples of secondary storage devices :
floppy disks, hard disks, and optical disk drives.
1-Floppy Disk Drives (FDD)
- Floppy disk called diskettes : are Portable or removable
storage media , inexpensive.
- Typically used to store and transfer small word
processing, spreadsheet, and other types of files.
- Also called flexible disks and floppies
- Stores 100 MB, 250 MB or 750 MB capacity
2-Hard Disks
* Faster than a floppy diskette
* Large capacity
*Today the standard hard disk stores 150 GB or
Types of Hard Disks
1- Internal Hard Disk
2- External Hard Disk
Internal Hard Disk
- Located inside the system unit
-Used for storing the operating system, other
programs, and large data files
- You should perform routine maintenance and
periodically backup all important files
Internal Hard Disk
External Hard Disk
*An external hard disk is easy to use.
*Located outside the system unit .
*The same as internal hard disk, more
expensive .
3- Optical Disks
- Use laser technology to provide high capacity
- It is flat, circular, plastic or glass disk on which data is
stored in the form of light and dark pits.
- The two most common are :
1-Digital Versatile Disc (DVD)
2-Compact Disc (CD)
3- Optical Disks
• Compact, high capacity form of permanent storage (up to
50 gigabytes of data).
• Optical discs are read by an optical disc drive.
• Laser beam writes by creating a pattern of pits (holes) and
lands (flat areas) to encode data bits.
• Laser beams reflect off the pits and lands to read the data.
• Rotational speed determines how fast data can be
transferred from the CD.
• Optical disks come in many different sizes.
• Most common is 4 ¾ inches.
• Stored in a protective case called jewel boxes.
Compact Disc (CD)
*Three basic types of CD’s :
-Read only: CD-ROM
-Write once: CD-R
-Rewriteable: CD-RW
Compact Disc
1-Read only CD-ROM: compact disk read only memory
and cannot be erased or modify contents.
2-Write once CD-R: ( compact disk-recordable)
disk you can write to only once.
3- Rewriteable CD-RW: (compact disk-rewritable)
Erasable disk you can write on many times , that can
be erased and written to with the new information.
Digital Versatile Disc (DVD)
*Digital Versatile Disc or Digital Video Disc (DVD)
*Similar to CDs, but can store more data
*Three basic types:
-Read only: DVD-ROM
-Write once: DVD+R; DVD-R
-Rewritable: DVD+RW; DVD-RW; DVD-RAM
1- Read only -DVD-ROM: Known as DVD players.
Used for videos.
2-Write once -DVD-R and DVD+R: Write once format
Two competing write once formats.
Used to create permanent archives for large amounts
of data and to record videos.
3-DVD-RAM or DVD+RW or DVD-RW– rewritable:
Use to store video from camcorders and developing
large multimedia presentations that include
extensive graphics and video
Other Types of Storage
1) Solid-state storage
• Flash memory cards.
• USB drives .
2) Magnetic tape.
• VCR tape (Video Cassette Recorder ).
Other Types of Storage
Solid-state storage
• No moving parts.
• Reliable, but expensive.
• Requires less power.
Magnetic tape
• Slower sequential access.
• Stores data and programs.
• Used for making backups of data.
Solid-State Storage
• Flash memory cards :
- Widely used in notebook computers
- This type of storage device has no moving parts.
- They are commonly used in many electronic devices,
including : digital cameras, mobile phones, laptop
computers, MP3 players, and video game consoles.
Solid-State Storage
• USB drives
- Also known as flash drive , pen drive , or key
- Connects to a USB port
- Easy to use and flexible, a cheap .price, called a
removable disk, multiple forms
Identify the Device
Identify the Device