3. 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
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5. 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
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6. 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
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7. 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
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8. 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
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10. 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
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11. 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
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13. 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
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14. 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 14
16. 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
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17. 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
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18. 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
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19. 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
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20. 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
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22. 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
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24. 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
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25. 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
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26. 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)
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27. Some Important long Questions
1. What are storage mediums available for devices?
2. Distinguish between Sequential and Direct access?
3. What are features/characteristics of Storage devices?
4. Explain the storage mechanism working of Optical Disks.
5. What is SSD and what type storage devices are built on this technology.
6. List down different types of memory cards
7. Distinguish between Primary and Extended Partition.
8. What is cloud storage? How is it different from traditional hard drive?
*note: Please don’t limit yourselves to these long questions only, examiner
can ask you about same material in different context.
You can extract several short questions as subset of these long questions.
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28. 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
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