Hard disk and optical disk

1. HARD
DISK
OPTICAL
DISKS
&

2. Definition of a Hard Disk
•To many users, the hard disk drive is the most important and yet the most mysterious pa
rt of a computer system.
•A hard disk drive is a sealed unit that a PC uses for non-volatile data storage.
Non-volatile, or semi-permanent, storage means that the storage device retains the data e
ven when no power is supplied to the computer.
•Why the name hard disk.?
•Also called as fixed disk.

3. Hard Disk Drive Operation
•The basic physical construction of a hard disk drive consists of spinning disks with heads that m
ove over the disks and store data in tracks and sectors.
•The heads read and write data in concentric rings called tracks, which are divided into se
gments called sectors.
•Hard disk drives usually have multiple disks, called platters, that are stacked on top of each
other and spin in unison, each with two sides on which the drive
stores data. Most drives have two or three platters, resulting in
four or six sides.
•The identically aligned tracks on each side of every platter
together make up a cylinder.

4. •Head crash?.
•Special magnetic read /write head s are mounted onto slider that are used to either record data
onto the disk or read data from it.
•The heads move across the disk in union; they cannot move independently because they
are mounted on the same carrier or rack, called an actuator.
•The disk controller is attached to the hard disk drive that handles the read /write
commands issued by the operating system.
•Each read/write command specifies a disk address
that comprises the surface number, track no, and
sector number.
•With this info. The read /write head moves to the
desired sector that can be read from or write to.
Hard Disk Drive Operation

5. •In most of the cases the heads do not touches the platters during the operation.!!!!
•Components.
• Disk platters
• Read/write heads
• Head actuator mechanism
• Spindle motor (inside platter hub)
• Logic board (controller or Printed Circuit Board)
• Cables and connectors
• Configuration items (such as jumpers or switches)
Hard Disk Drive Operation

8. Optical Disks
•Optical disk is flat, circular disk coated with reflective material.
•Bits are stored in the form of highly reflective are & significantly less reflective area.
•Data is stored with the help of lasers and diodes.
•Surface is coated with thin layer of metal which acts as reflecting surface.
•Storage organization of Optical disk.????
•Types of OD’s
•CD
•DVD
•Blu Ray

9. Optical Disks Access Mechanism

10. Optical Disks Access Mechanism

11. Compact Disk
•A CD is made of a polycarbonate wafer, 120mm in diameter and 1.2mm thick, with a 15mm hol
e in the centre. This wafer base is stamped or moulded with a single physical track in a
spiral configuration.
Types of CD
•CD ROM
•CD R
•CD RW

12. Compact DiskCD-ROM drives operate in the following manner
1. The laser diode emits a low-energy infrared beam toward a reflecting mirror.
2. The servo motor, on command from the microprocessor, positions the beam onto the correct
track on the CD-ROM by moving the reflecting mirror.
3. Light is gathered and focused through the first lens beneath the platter, bounced off the mir
ror, and sent toward the beam splitter.
4. The beam splitter directs the returning laser light toward another focusing lens.
5. The last lens directs the light beam to a photo detector that converts the light into electric
impulses.

13. •DVD stands for digital versatile disc and in simplest terms is a high-capacity CD. In fact,
every DVDROM drive is a CD-ROM drive; that is, they can read CDs as well as DVDs (discs
)
•DVD uses the same optical technology as CD, with the main difference being higher density
DVD technology is similar to CD technology. Both use the same size discs with pits and lands
stamped in a polycarbonate base. Unlike a CD, though, DVDs can have two layers of
recordings on a side and be double-sided as well.
Digital Versatile Disk

14. •The manufacturing process is largely the same, with the exception that each layer on each side
is stamped from a separate piece of polycarbonate plastic and are then bonded together to for
m the completed disc.
•The main difference between CD and DVD is that DVD is a higher-density recording read by a l
aser with a shorter wavelength, which enables more information to be stored. Also, whereas CD
s are single-sided and have only one layer of stamped pits and lands, DVDs can have up to two l
ayers per side and can have information on both sides.
Digital Versatile Disk

15. Blu Ray Disk
•It is an optical storage device which is used to record and playback high definition video and
audio.
•Also used to store images and other files.
•For recording is uses Blue violet rays having shorter wavelength than red laser.

16. Advantages
•Larger capacity
•More data stored in less space.
•Life span is more.
•Low cost
•Not affected by magnetic field.
•Tougher than other.
•Portable

17. Disadvantages
•Requires both hardware as well as software for oprations.
•Data access speed is slow.
•Drive mechanism of an optical disk is more complicated than the magnetic disks.