2. STORAGE DEVICES
• A data storage device is a device for recording
(storing) information (data).
• CD, Hard Disk and Flash media are the main storage
devices used today.
3. COMPACT DISC
• Compact Disc (CD) is a circular disc of diameter of 120 millimetres
(4.7 in)
• A CD can hold up to 80 minutes of uncompressed audio or 703 MB.
The below diagram shows the construction of a CD.
4. Understanding the CD
• A CD has a single spiral track of data
circling from the inside of the disc to the
outside.
• Spiral track starts at the centre means
that the CD can be smaller than 4.8
inches (12 cm) if desired.
• Mini CD of diameter only 2.4 inches (
6cm) used for delivering device
drivers.
5. Understanding the CD:
Bumps
• A laser of wavelength 780 nm is used to ‘burn’ pits (bumps) on CD track.
• The elongated bumps that make up the track are each 0.5 microns wide,
a minimum of 0.83 microns long and 125 nm high.
• If you could lift the data track off a CD and stretch it out into a straight
line, it would be 0.5 microns wide and almost 3.5 miles (5 km) long!
6. CD Player
• A laser and a lens system focus in on and read the bumps.
• The CD layer reflects the laser, at pits reflected value is a 0
and else it is 1.
• A tracking mechanism moves the laser assembly so that the
laser's beam can follow the spiral track.
• A drive motor spins the disc at a speed between 200 to 500
rpm.
7. Digital Versatile Disc
• A DVD has almost 6 times (up to 4.7 GB) data storage
capacity then a CD.
• The more storage capacity of a DVD is duo to less separation
between tracks and less size of track.
8. Flash Drives
• Flash memory refers to a type of computer technology that stores
data, does not need constant electricity, and can be electrically
erased and reprogrammed.
• Flash memory is used in many different appliances including memory
cards, PDAs.
• Information is stored in an array of memory cells made from floatinggate (FG) transistors
10. Working of Flash Drives
• The top gate is called the control gate while the bottom is
called the floating gate.
• The floating gate is completely insulated with an oxide layer.
Each memory cell of a USB flash drive is a floating-gate
transistor.
• When an electron is attached to the floating gate, it is
trapped within the oxide layer and causes a difference in the
voltage of the control gate.
• When this is measured as a whole, each memory cell makes
up a 1 or 0 in binary code, depending on whether it is
storing an electron or not.
11. NOR Flash Memory
Developed to replace read only memory
Full address and data buses allow random access to any
memory location
Can access any memory cell
Slow sequential access
NAND Flash Memory
Developed to replace hard disks
Sequential-accessed command and data registers replace the
external bus of NOR
Decreases chip real estate
Can only access pages
Faster sequential access
12. Hard Disks
• A hard disk drive (HDD) is a data storage device used for storing and
retrieving digital information using rapidly rotating disks (platters)
coated with magnetic material.
• An HDD retains its data even when powered off.
• Data rate - The data rate is the number of bytes per second that the
drive can deliver to the CPU. Rates between 5 and 40 megabytes per
second are common.
13. Understanding the Hard Disk
• The platters - These typically spin at 3,600 or 7,200 rpm when the drive is
operating. In order to increase the amount of information the drive can
store, most hard disks have multiple platters.
• The arm - This holds the read/write heads and is controlled by the
mechanism in the upper-left corner. The arm is able to move the heads
from the hub to the edge of the drive.
14. • Data is stored on the surface of a platter in sectors and tracks.
• Tracks are concentric circles, and sectors are pie-shaped wedges on a
track.
• A sector contains a fixed number of bytes -- for example, 256 or 512.
• The process of low-level formatting a drive establishes the tracks and
sectors on the platter.
• The process of low-level formatting a drive establishes the tracks and
sectors on the platter.
15. • An HDD records data by magnetizing a thin film of ferromagnetic
material on a disk.
• Sequential changes in the direction of magnetization represent binary
data bits.
• The data is read from the disk by detecting the transitions in
magnetization.
