STORAGE DEVICES

Presentation By:

Saurabh Mishra

• 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.

STORAGE DEVICES

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.

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.

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!

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.

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.

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 floating-gate (FG) transistors

Flash Memory Cell

• 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.

Working of Flash Drives

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

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.

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.

• 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.

• 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.

References

• computer.howstuffworks.com• wikipedia.com• Google Images