2. What is Storage
• Storage holds data, instructions and
information for future use.
– All the programs when started are loaded
from a storage device onto computer memory
– Users store a variety of data on mainframes,
servers, desktops, notebooks, handheld
devices, smart phones etc
3. Storage Medium
• A storage medium is the physical material
on which a computer keeps data,
instructions and information.
– Hard disks, CDs, DVDs, memory cards, USB
flash drives etc are all storage mediums or
secondary storage devices
– Storage capacity is the number of bytes a
storage medium can hold
4. Storage terms
• 1 KB = 2
10
Bytes = 1,024 bytes
• 1 MB = 2
20
Bytes = 1,048,576 bytes
• 1 GB = 2
30
Bytes = 1,073,741,824 bytes
• 1 TB = 2
40
Bytes = 1,099,511,627,776 bytes
– A storage medium is non-volatile, that is, items
on storage medium remain intact even when
power is removed
5. Storage device
• A storage device is the computer
hardware that records and/or retrieves
items to and from the storage media.
– Writing is the process of transferring data,
instructions and information from memory to
storage medium.
– Reading is the process of transferring these
items from a storage medium into memory.
6. – When storage devices write data onto storage
medium, they are generating computer output
– When storage devices read from storage
media, they are generating input for the
computer.
* however, storage devices are not categorised
into input or output devices
7. Speed
• The speed of storage devices and
memory is defined by access time.
– The time required to locate an item on a
storage medium
– The time required to deliver an item from
memory to the processor
• Access time of storage devices is slow as
compared to memory devices
9. Magnetic Disks
• Magnetic disks use magnetic particles to
store items on a disk’s surface
– Each particle on the magnetic disk represents
a bit
– Formatting is process of dividing the disk into
tracks, sectors and clusters (allocation unit)
10.
11. Hard Disk
• A hard disk is a storage device that contains one or more
inflexible magnetic disks
12. • The magnetic disks in a hard disk rotate at
a speed from 5,000 to 15,000 rpm
• The data transfer rate of hard disks range
from 15 mbps to 320 mbps
• Hard disks improve their access time by
using disk caching
– Disk cache is a memory chip on hard disk that
stores frequently accessed items
13. • A group of two or more integrated hard
disks is called RAID (Redundant Array of
Independent Disks)
• Miniature hard disks are present in digital
cameras, portable media players, smart
phones etc
• A pocket hard drive or portable hard drive
also has a miniature hard disk
• External or removable hard disks
14. Hard Disk Controller
• A disk controller consists of a special-
purpose chip and electronic circuits that
control the transfer of data.
– An interface is required by the hard disk
controller to transfer data to and from the hard
disk
• SATA (Serial Advanced Technology Attachment)
• EIDE (Enhanced Integrated Drive Electronics)
• SCSI Interfaces
• SAS (Serial Attached SCSI)
15. Online storage
• Online storage is a service provided on
the web that gives hard disk storage to
users for free or for a nominal monthly fee
– To access data from other computers
– To store files like audio, video and graphics
on the internet instead of downloading onto
local hard disk
– To allow others to access your files
– To store backups
16. Other storage media
• Floppy disks : A flexible plastic film with a
magnetic coating
• Optical discs: A storage media that
consists of portable disc made of metal,
plastic and lacquer that is written and read
by a laser
– Read/write feature
– Double-sided discs
17. Disc type Features
CD-ROM Read only
CD-R Read and write
CD-RW Read, write and
erase
DVD-ROM, BD-ROM, HD DVD-
ROM
Read only
DVD-R, BD-R, HD DVD-R Read and write
DVD-RW, DVD-RAM, BD-RE, HD
DVD-RW
Read, write and
erase
18. • PC cards and Express cards (developed
by Personal Computer Memory Card
International Association)
• Flash memory cards (solid state media)
– Secure Digital (SD)
– Mini SD
– USB flash drives
– Smart card (sim, visa card, master card etc)
– Enterprise storage
