1. Introduction to Computing
Lecture-3-Storage Devices (Optical Devices)
Muhammad Hafeez
Department of Computer Science
GC University Lahore

2. Today’s Agenda
Working of Optical Devices

3. Optical Disk
A storage medium that consist of flat, round, portable disk made of metal or plastic, written and read by laser.
Three types of optical disks are: CD
DVD
Blu-Ray

4. Characteristics of Optical Disk
Store items by using microscopic pits (indentations) and lands (flat areas)
A high power laser light create the pits
A low-powered laser light read items from the disk by reflecting light through the bottom of disk.
Reflected light is converted into a series of bits a computer can process.
A land cause 1 and a pit cause 0.

5. Characteristics of Optical Disk
Optical disk store data on single spiral shaped track.
This track is evenly divided into sectors

6. Working of Optical Disk/ Access Mechanism

7. Working of Optical Disk/Access Mechanism

8. Storage on Optical Disk in a single Track

9. Storage Organization
One spiral track helps reading/ writing large volume of data such as audio/ video.
However, it causes slow random access of data (sectors are not easily tracked)
Spiral track divided into equal sized tracks enable large packing of data at maximum density

10. Storage Capacity Cost per byte is low
An optical drive with capacity of 650 MB can store 250,000 pages of printed text.
More suitable for multimedia and software distribution
A disk with 330,000 sectors each having 2350 bytes makes up
330,000 x 2350 = 776 x 106 = 776 MB

11. Types of Optical Disks WORM Disck/ CD-Recordable: Write One Read Many
CD-RW
DVD (Digital Video/ Versatile Disk)

12. Questions
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