This book serves as a comprehensive guide for BS and ADP disciplines, covering computer concepts and practical skills related to Windows 7 and MS Office 2010. Key topics include various storage devices like hard disks, floppy disks, and optical disks, highlighting their characteristics, access modes, storage capacities, and data transfer rates. Additionally, it details the processes of writing and reading data, emphasizing the differences between magnetic storage and optical storage technologies.

1. This book is compiled for all
BS/ADP disciplines. First 10
chapters (from page 1 to 205)
included in this book are
related to computer concepts
and other chapters are related
to the Windows 7, MS office
2010 (Word, Excel, PowerPoint,
Access), and InPage 2000 with
practical.

2. Chapter 4
Storage Devices
INTRODUCTION TO COMPUTER

3. Contents
• Storage Medium
• Storage Device
• Magnetic Storage
• Optical Disc
• Solid State Storage Devices
• Cloud Storage
• Disk Partitions

4. Storage Medium
Chapter 4 - Storage Devices

5. Storage Medium
• Main memory or RAM is volatile
• It cannot be used as permanent storage because when computer is switched off, its contents are
erased
• Its storage capacity is also very small
• Storage medium is used to store data and programs permanently for later use
• It is non-volatile
• A storage medium is also called secondary storage, auxiliary storage, mass storage, or backing
storage
• Examples  hard disk, solid-state drives, memory cards, USB flash drive, optical disc, magnetic
stripe card, and smart cards
• Every computer or mobile device stores software and information on the storage medium
• For example, during booting process, a computer locates an operating system in a storage medium (such as a
hard disk) and loads it into memory (RAM)
• Similarly, when a user issues a command to open an application program, OS locates program in a storage
medium and loads it into RAM
• Storage capacity of the storage medium is the number of bytes storage medium can hold
• Storage capacity of the storage medium is up to Terabytes (TB) for personal computers

6. Storage Medium

7. Storage Device
Chapter 4 - Storage Devices

8. Storage Device
• A storage device is a computer hardware component that writes and reads
information or instructions to and from the storage media
• Examples of most popular storage devices are hard disk drive, CD/DVD drive,
and USB flash drive
• A computer performs two operations on the storage devices
• Writing  In a writing process, storage device records/stores information or
instructions from memory to a storage medium
• Reading  In a reading process, storage device transfers information or instructions
from storage medium into computer’s memory (for use by OS or application program)
• When a storage device writes data (or programs) on storage medium, it
performs a function as an output device
• Similarly, when a storage device reads data from disk and loads it into RAM, it
performs a function as an input device

9. Storage Device
Characteristics of Storage Devices
•Access Mode
• It is the sequence or order in which the storage medium can be accessed
• There are two major access modes  sequential and random
• Sequential access mode
• Storage medium can be accessed only in serial order
• Magnetic tape is a sequential access storage device
• Random access mode
• Storage medium can be accessed randomly or directly
• RAM and hard disk are random access storage or memory devices

10. Storage Device
Characteristics of Storage Devices
Speed
• Speed of storage devices and memory is defined by access time and data transfer rate
• Access Time
• Time taken by storage device to locate data items from a storage medium
• Usually, access time is measured in nanoseconds (ns)
• A nanosecond is one-billionth of a second
• Access time of sequential access memory devices is larger than that of random access memory
devices
• A memory device that has less access time is faster
• For example, accessing data in RAM can be more than 200,000 times faster than accessing data
on a hard disk
• Data Transfer Rate
• Time taken to transfer data to and from storage device
• It is measured in kilobytes per second (KBps), or MBps, or GBps

11. Storage Device
Characteristics of Storage Devices
Storage Capacity
• Maximum amount of data that can be stored on the storage medium is called
storage capacity
• Today, storage capacity of different storage devices is up to terabytes (TB)
• Storage devices with large storage capacity can be used to save a large
amount of data

12. Magnetic Storage
Chapter 4 - Storage Devices

13. Magnetic Storage
• Magnetic storage is one of the most widely used secondary storage in
computers
• It consists of a magnetic medium on which information is stored
• Magnetic disks (i.e. hard disk) and magnetic tapes are examples of magnetic
storage
• Disk drive or tape drive is used to write data on the disk/tape or read data
from the disk/tape
• Read-write head of the disk drive or tape drive performs read and write
operations on the magnetic medium

14. Magnetic Disk
• A magnetic disk is a thin circular metal or plastic disk
• It is coated with magnetic material (ferrous oxide) on which data/information is stored
• Data/information is accessed directly or randomly
• Disk drives are used to write and read data/information to and from magnetic disk
• Hard disk, floppy disk, and zip disk are examples of magnetic disks (The shape of zip disk is
similar to floppy disk)
• Today, hard disk is commonly used in computers as secondary storage
• Floppy disks and zip disks are not in use nowadays
• These disks have been replaced by optical disks and USB flash drives which are more
reliable and have large storage capacity

15. Magnetic Disk
Organizing Data on Magnetic Disk
• Before storing data on magnetic disk, it is prepared through OS
• Actually, disk’s surface is magnetically mapped
• Process of mapping the surface of disk is called formatting or initializing
• During formatting a disk, OS divides disk into different circles called tracks
• Usually, a floppy disk has 80 tracks on each side of the disk
• Similarly, a hard disk may have a hundred tracks on each side of each platter
• Each track is further divided into pie-shaped areas called sectors
• Information is stored in sectors, in one sector, 512 bytes are stored
• Disk surface may have some bad sectors
• When a disk is formatted, OS marks bad sectors as unusable and these are not used
to store data
• The number of tracks on the disk and number of sectors per track depend
upon the density of the disk
• Each track and sector is assigned a unique number or address
• Data is read or written with reference to sector numbers
• Computer goes directly to the specified sector and reads or writes data
• Disk drive reads or writes the whole sector at a time

16. Magnetic Disk
Floppy Disk
• A floppy disk is a portable magnetic storage media
• It is also called simply a diskette
• The standard floppy disk size is 3.5-inch
• Storage capacity of the floppy disk is very low (i.e. 1.44 MB for 3.5-inch floppy
disk)
• Data access speed of the floppy disk is slower than the hard disk
• Today, floppy disks are rarely used
• These disks have been replaced by optical disks and USB flash drives which are
more reliable and have large storage capacity
Zip Disk
• ZIP disk is similar to a floppy disk but its storage capacity is about 100 (or more)
times greater than a floppy disk
• Today, zip disk is rarely used

17. Magnetic Disk
Hard Disk
• Most application programs and OS require hard disk for installation and operation
• A hard disk is also called a hard disk drive or hard drive
• Most personal computers and laptops contain at least one hard disk
• However, large computers contain multiple hard disks
• Hard disk contains multiple metal circular platters (disks) mounted on a central spindle
• Each platter is coated on both sides with magnetic material
• Both surfaces of each disk or platter are used to store information except for top and bottom platters
• The surface of each disk (platter) is logically divided
into concentric circles called tracks
• Each platter contains many tracks
• A track is divided into sections called sectors
• Data/Information is stored in sectors in the shape of
tiny magnetized spots called bits
• The set of tracks of different platters that are at a
particular head position is known as a cylinder

18. Magnetic Disk
Hard Disk
• Hard disk and drive is a single unit
• It includes hard disk and motor that rotates platters
• All platters move together with high speed
• They rotate from 5400 to 15000 revolutions per minute (rpm)
• Each platter has two read/write heads, one for each side
• Hard disk has also arms that move the read/write heads to the proper location on the
platter to read or write data
• Entire unit is enclosed in an airtight, sealed case to protect it from dust
• A standard or traditional hard disk is not portable
• It is permanently fixed in the system unit
• It is because hard disk is also referred to as a fixed disk
• However, portable hard disks are also available

19. Magnetic Disk
Hard Disk
• A hard disk is formatted before storing data on it
• OS makes logical tracks on both sides of each platter and divides each track into
sectors
• Each platter of hard disk has a very high density
• A large number of tracks are made on each surface of the platter
• If a computer contains only one hard disk, OS assigns it as drive letter C:
• Additional hard disks (logical hard disks) are assigned the next available drive letters
• Today, storage capacity of hard disk in PCs is up to 8 TB (Tera Bytes) or more
• Storage capacity of a hard disk is determined by the number of platters it contains
and the density of the platter
• Accessing speed of hard disk is also very high as compared to other secondary
storage devices
• It is from 5 to 15 MBps (megabytes per second)

20. Magnetic Disk
Hard Disk
Hard Disk Performance
• Performance of hard disk depends upon following factors
• Seek Time
• Seek time is the time required to move a read/write head to a particular cylinder or track
• Seek time is variable; because it will take more time to reach track 300 from track 1 than to reach track 100
• Therefore, seek time is expressed as average seek time
• It is measured in milliseconds (ms)
• Rotational Latency
• Once a cylinder or track is selected, disk controller waits until read/write head reaches an appropriate sector
• Time required to reach the head at the beginning of an appropriate sector
• It is measured in milliseconds (ms)
• Transfer Time
• Transfer time is the time required to transfer data, read from the disk into the main memory
• Alternatively, it is the time required to write data on the disk from the main memory
• Access Time
• Access time is the sum of average seek time, rotational delay, and transfer time
• Mathematically it is written as: Access Time = Average Seek Time + Rotational Latency + Transfer Time
• Once read/write head is in position, read or write operation is performed
• Typically, a disk can transfer several megabytes of data per second

21. Magnetic Disk
External Hard Disk
• External hard disk is separate magnetic storage which is an external part of
computer
• It means that external hard disk is not fixed in the system unit
• It can be connected to the computer through a USB port or FireWire port or
wirelessly
• Some external hard drives contain built-in wireless functionality to communicate
with the computer through a Wi-Fi connection
• Like an internal hard disk, an external hard disk also consists of multiple platters
that are air-sealed inside a casing
• Storage capacity is very high which is up to 4 TB or more
• It is used for backup of data and sharing data and programs from one computer
to another
• Data transfer rate of external hard disks is slower than the internal hard disk

22. Hard Disk
• May contain multiple metal plates or disks
• Fixed inside the system unit and it is not
portable
• More expensive than a floppy disk
• Storage capacity is very large which is up
to 8 TB or more
• Data access speed is faster than a floppy
disk
• Today, it is commonly used for data
storage
• Has a low chance of damage
• Reliable storage media
Floppy Disk
• Contains only one plastic disk
• Portable
• Less expensive than a hard disk
• Storage capacity is very low which is
only up to 1.44MB
• Data access speed is slower than a
hard disk
• Today, it is rarely used for data
storage
• Has a high chance of damage
• Not reliable storage media

23. Magnetic Tape
• Magnetic tape is the most popular and oldest storage medium
• It consists of a plastic strip (or ribbon) with a magnetic coated material, which
can be magnetized
• Data/information is stored on the tape in the form of magnetized and non-
magnetized spots representing 1’s and 0’s respectively
• Magnetic tape is either in the form of a cassette or a big reel

24. Magnetic Tape
• Like magnetic disk, magnetic tape is also formatted before storing data on it
• Tape is divided into vertical columns called frames
• Each frame is further divided into horizontal rows called tracks (or channels)
• Each frame represents one character and each track of frame stores one bit for the code
of the character
• Typically, a frame is divided into 9 tracks
• First 8 tracks are used for recording the code of a specific character and the ninth track
is used for recording the parity bit or check bit
• Parity bit is used to detect errors during reading or writing data on the tape

25. Magnetic Tape
• Magnetic tape is used for storing a large amount of data (especially used for
backing up of data)
• Amount of data that can be stored on a tape depends upon its length, its type,
and density
• Today, storage capacity of magnetic tape is up to 5 TB or more
• It is used with minicomputers and mainframe computers for data backup
• It is an inexpensive (cheap) storage device
• However, it is slow in data accessing because it is a sequential access storage
device

26. Magnetic Tape Drive
• A magnetic tape drive is a storage device that writes/reads data to and from a
magnetic tape
• The write head encodes the magnetic signals on the tape as it moves across
the write head
• Similarly, the read head reads the stored data from tape and transfers it into
the RAM

27. Optical Disc
Chapter 4 - Storage Devices

28. Optical Disc
• An optical disc is a type of storage media that consists of a flat, round,
portable disc made of metal or polycarbonate plastic
• It is coated with a thin metal or plastic or other material that is highly
reflective
• Optical discs used in computers typically are 4.75 inches in diameter and less
than one-twentieth (1/20) of an inch thick
• Mini-optical discs are used in mobile devices that have a diameter of 3 inches
or less
• A large amount of data, software, movies, and songs, etc. can be stored on a
single CD
• Some optical storage media is read-only while others are read and write
• Spelling disk is used for magnetic media, while disc is used for optical media

29. Optical Disc
• An optical disc has a single spiral track that spirals from the center to outside
edge
• Information on the optical disc is stored in the form of microscopic pits (small
holes) and lands
• A binary digit ‘0’ is represented by a pit and a binary digit ‘1’ is represented by
a land
• Pits are tiny reflective bumps that are created with a laser beam
• Lands are flat areas separating the pits
• A land reflects laser light, which is read as binary digit 1
• A pit absorbs or scatters light, which is read as binary digit 0
• High-powered laser beam creates the pits
• A lower-powered laser light reads data from the disc
• Different types of optical discs
• CD
• DVD
• Blu-ray Discs

30. CD
• CD stands for Compact Disc
• It is an optical disc used for storing digital data
• It was originally developed for sound recording but now it is widely used for
storing computer data and programs
• Storage capacity of CDs ranges from 350 MB to 800 MB
• CDs are mostly used for storing huge amount of data, application programs,
operating systems, and device drivers
• Types of CDs
• Read-only (CD-ROM)
• Recordable (CD-R)
• Rewritable (CD-RW)

31. CD
CD-ROM
• CD-ROM stands for Compact Disc Read-Only-Memory
• CD-ROM is a type of optical disc
• A large amount of data can be stored on a single disc
• Once data/information is stored on CD-ROM, it becomes permanent and cannot
be modified
• Data/information can only be read
• That is why it is called Compact Disc Read Only Memory
• Manufacturers write data and software on CD-ROMs
• A standard CD-ROM is called a single-session disc because manufacturers write all
items or information on the disc at one time
• CD-ROM drive is used with a computer to read the information from the CD-ROM

32. CD
CD-R
• CD-R (CD-recordable) is an optical disc on which users can write data only once
but can read it many times
• CD-R is also known as WORM (Write Once, Read Many)
• Data written on CD-R cannot be erased
• Some CD-Rs are multisession optical discs
• Multisession means users can store information on part of disc at one time and
another part at a later time
• However, each part of CD-R can be written only one time, and the disc’s
contents cannot be changed
• Process of writing information on the optical disc is called burning
• CD-writer or recorder (or simply CD-R drive) is used to write data on CD-R discs

33. CD
CD-RW
• CD-RW (CD-rewritable) is an erasable multisession optical disc
• User can write and over-write data on the CD-RW disc many times
• CD-RW disc is also known as an erasable CD (or CD-E)
• However, the reliability of this type of optical disc tends to decrease, each time
we re-write data
• CD-RW drive is used to write/overwrite and read data to and from the CD-RW
• This drive is advanced and more expensive than a CD-R drive
• It can write/read data on both CD-R and CD-RW discs
• Today, most of the PCs have a CD-RW drive

34. DVD
• DVD stands for Digital Video Disc or Digital Versatile Disc
• A DVD is similar to a CD
• It has the same diameter and thickness as CD and is made up of the same material
• Data is also stored just like a CD on a spiral track in the form of lands and pits
(bumps)
• However, DVD has larger data storage capacity and higher resolution than CD
• Its data storage capacity is up to 17 GB or more
• DVD is specially used to store movie films
• It is also used to store huge amount of data, music, and software of large size
• DVD drive or DVD player is used to read the data stored on a DVD
• A DVD player can play CDs also
• Types of DVDs  read-only (DVD-ROM), recordable (DVD-R), and rewritable (DVD-
RW)

35. DVD
DVD-ROM
• DVD-ROM (DVD read-only memory) is similar to CD-ROM
• It is a high capacity optical disc that users can only read but not write or erase
• Only manufacturer writes information on DVD-ROM
• DVD-ROMs are used to store movies, music, and software
DVD-R
• DVD-R (DVD recordable) is similar to CD-R
• Users can write data only once but can read it many times
• Data written on DVD-R cannot be erased
DVD-RW
• DVD-RW (DVD-rewritable) is similar to CD-RW
• User can write and over-write data on DVD-RW many times

36. Blu-Ray Disc
• Blu-ray disc (BD) is a new type of optical storage device
• This storage device is reliable, faster, and has higher storage capacity than CD
and DVD
• Its storage capacity is up to 1000 GB or more
• Bumps (pits) on the Blu-ray disc are much smaller and very closely (tightly)
packed than DVD
• This increases the storage capacity of Blu-ray discs
• Blu-ray discs are better storage for storing movies because they require more
storage
• Blu-ray drive is used to read the information on the Blu-ray disc
• Some game consoles contain a Blu-ray drive

37. Solid State Storage Devices
Chapter 4 - Storage Devices

38. Solid State Storage Devices
• Solid-state storage device is also called a flash memory device
• It has no moving parts in it
• It is neither magnetic nor optical
• It contains a solid chip (an integrated circuit) that can store data
• Flash memory chips are a type of solid state storage media
• Information inside solid state storage media is stored and read electrically
• Most of the solid-state storage media are non-volatile
• Solid-state storage devices are widely used in PCs, PDAs, tablets, notebooks,
smartphones, digital cameras, portable media players, and other mobile devices
• Types of Flash Memory Devices
• Solid-state drives (SSDs)
• USB flash drives
• Memory cards

39. Solid-State Drive (SSD)
• Solid-state drive (SSD) is a storage device that typically uses flash memory to store data/information
• It contains its own processor to manage its storage
• It has faster access time than traditional hard disk drives
• SSD has no moving parts (mechanical components)
• SSD can be in the form of a flash memory chip installed directly on a motherboard or an adapter card
• It also may be housed in a separate casing that is connected to the motherboard
• External SSDs are also available
• SSDs are used in all types of computers such as desktops, servers, laptops, tablets, and mobile devices (such as
DV cameras, portable media players)
• Some computers have both a hard disk and an SSD
• They are available in different sizes such as 1.8 inches, 2.5 inches, and 3.5 inches
• Storage capacity of SSDs can be up to 4 TB or more
+ Faster access time and data transfer rate
+ More durable and has a longer life
+ Light-weight
+ Generates less heat
+ Consumes less power
+ More reliable
- In case of SSD failure, recovery of data can be more difficult than hard disk
- More expensive than a hard disk

40. USB Flash Drive
• USB flash drive is also known as a pen drive or thumb drive
• It is a flash memory device
• It is connected to a USB port in a computer or mobile device for writing and
reading data
• It is a non-volatile memory
• It is small in physical size and light-weight storage device
• Today, USB flash drive is commonly used as portable storage
• Today, USB flash drives are widely used in PCs and other mobile
computers/devices for transferring data from one computer/device to another
• USB flash drives are available in different shapes, sizes, and storage capacities
• Storage capacities of USB flash drives can be up to 256 GB or more

41. 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
• Flash memory cards are widely used in digital cameras, mobile phones, PDAs,
video games, and other portable devices
• A memory card can be inserted into a slot in a computer, mobile device, or
card reader/writer
• Usually, card reader/writer is used to store or read information to and from
memory cards
• A card reader/writer is usually connected to the USB port of computer
• Some computers and photo printers have built-in card readers/writers or slots
that read memory cards

42. Memory Card
• Types of flash memory cards
• CompactFlash (CF)
• Used in digital cameras, smartphones, PDAs, photo printers, portable media players, notebook computers,
& desktop computers
• Its storage capacity is up to 512 GB or more
• Secure Digital High Capacity (SDHC)
• It is used in digital cameras and video recorders
• Its storage capacity is up to 32 GB or more
• microSDHC
• It is also used in smartphones, tablets, portable media players, and handheld navigation devices
• Its storage capacity is up to 32 GB or more
• xD Picture Card
• It is used in digital cameras and photo printers
• Its storage capacity is from 256 MB to 2 GB or more
• Memory Stick & Memory Stick Micro (M2)
• These both types of flash memory cards are used in smartphones
• Storage capacity is up to 32 GB or more

43. Cloud Storage
Chapter 4 - Storage Devices

44. Cloud Storage
• Cloud storage is also known as online storage
• It is an Internet service that provides remote storage to users
• This service is provided and managed by cloud storage service providers on
their storage servers
• Many cloud storage service providers are available on the Internet
• They offer different types of storage services for users
• Some cloud service providers offer limited storage service for free of cost
• We can get more storage services through some payment through credit cards
• Some important cloud storage services are Dropbox, Google Drive, SkyDrive,
and iCloud

45. Cloud Storage
Dropbox
• Dropbox is a popular cloud storage service that is used for storing and sharing
files online
• Files are stored on Dropbox’s servers
• Dropbox was launched in 2007 by two American students
• Today, Dropbox service is used by more than 50 million users
• Dropbox offers free storage accounts up to 2GB
Google Drive
• Google Drive is a cloud storage service from Google and was launched in 2012
• It is also used for storing and sharing files online
• Google Drive provides 15 GB of free storage

46. Cloud Storage
SkyDrive (OneDrive)
• SkyDrive is a cloud storage service similar to Dropbox and Google Drive
• It is developed by Microsoft
• Now SkyDrive is called OneDrive (because Microsoft renamed its name from
SkyDrive to OneDrive)
• It provides up to 15 GB of free space for storing files
iCloud
• iCloud is a cloud storage service and cloud computing service from Apple Inc
• It was launched in 2011
• This service provides its users to store files on Apple cloud servers
• It provides up to 5 GB of free space for storing files

47. Disk Partitions
Chapter 4 - Storage Devices

48. Disk Partitions
• Logical division of a hard disk into multiple parts or sections is called disk
partition
• Hard disk can be divided into multiple partitions (parts) during its formatting
process
• Each part of the physical disk drive is treated as a separate disk drive such as C
drive, D drive, and E drive
• Some OS such as Windows and Linux require multiple partitions of hard disk
• Disk partitioning allows for installing and running multiple OS on the same
computer
•Types of disk partitions
• Primary Partition
• Extended Partition

49. Primary Partition
• Partition on which OS is installed is called a primary partition
• It is also called system partition
• It contains OS folders and files
• Windows and other OS boot from a primary partition
• Primary partition may use entire disk or only part of it
• We can create a maximum of four primary partitions on a hard disk

50. Extended Partition
• Extended partition is a part of a physical hard disk
• A hard disk can have only one extended partition
• It cannot be formatted and assigned any drive letter
• Extended partition is used only for creating multiple logical partitions (logical
drives)
• Each logical partition is formatted and assigned a unique letter
• In this way, multiple logical hard disk drives can be created
• Data of users is usually stored on logical partitions (logical drives)

51. For more details, refers to
PM Series
Introduction to Computer
by
CM Aslam, Aqsa Aslam, Mussadiq Fida, & Mudassir
Ahmad
Publisher:Majeed Sons
22- Urdu Bazar, Lahore