INTRODUCTION TO COMPUTING LECTURE3 STORAGE DEVICES OPTICAL DEVICES

INTRODUCTION TO COMPUTING LECTURE-3 -STORAGE DEVICES (OPTICAL DEVICES) MUHAMMAD HAFEEZ DEPARTMENT OF COMPUTER SCIENCE GC UNIVERSITY LAHORE

TODAY’S AGENDA l Working of Optical Devices

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

CHARACTERISTICS OF OPTICAL DISK l l l 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.

CHARACTERISTICS OF OPTICAL DISK l l Optical disk store data on single spiral shaped track. This track is evenly divided into sectors

WORKING OF OPTICAL DISK/ ACCESS MECHANISM

WORKING OF OPTICAL DISK/ACCESS MECHANISM

STORAGE ON OPTICAL DISK IN A SINGLE TRACK

STORAGE ORGANIZATION l l l 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

STORAGE CAPACITY l l l 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

TYPES OF OPTICAL DISKS l WORM Disck/ CD-Recordable: l Write One Read Many CD-RW l DVD (Digital Video/ Versatile Disk) l

QUESTIONS l ? ? ? ? ? ? ?