2. CD-ROM By Sadaf Khan Javaria Khalid SumayyahIfra
3. Index Storage devices. Categories of storage devices. CD-ROM. Structure of CD-ROM. Reading of CD-ROM. Pits & Lands. Reading Speed. Writing of CD-ROM. File System. Tracks & Sectors. Writing Methods. 03
4. Storage Capacity. Advantage of CD-ROM Disadvantages of CD-ROM Summary. References. Question & Answer Session 04
5. The storage devices store data –even when the computer is turned off. It is used to keep important data and files which are of regular use on permanent basis. Storage Devices 05
6. Categories of Storage Devices The two main categories are magnetic storage and optical storage. Optical Storage Magnetic Storage 06
7. CD-ROM CD-ROM stands for compact disc read-only memory. It is an optical disc used to store digital data, originally developed for storing digital audio.
8. CD Structure A CD is flat, round, portable metal disc, which is coated with a thin metalor plastic or other material that is highly reflective. It is usually 0.75 inches in diameter and less than one-twentieth of an inch thick. 08
10. Reading data from CD-ROM A CD-ROM drive reads digital data from a spinning disc by focusing a laser on the disc’s surface. Some areas of the disc reflect the laser light into a sensor, and other areas scatter the light. 10
11. Pits and lands The CD-ROM holds digital data. Data is stored in the form of lands and pits. Lands are flat areas on the metal surface. Pitsare depressions or hollows. 11 Reading logic ‘1’ Reading logic ‘0’
12. Reading Speed Reading speed is measured in kB/s Reading speed determines the transfer of data in one second. 1× or 1-speed which gives a data transfer rate of 150 kB/s in the most common data format. Maximum speed available today is 52x. 12
14. Writing Data On CD-ROM A laser is used to heat a chemical dye in the disc to create marks that will be read as data. As marks (pits) are created through burns, this process is also referred as burning. Burning a CD is comparatively slower than reading it. Maximum burning speed is 32x. 14
15. File System The format of the CD (file system) describes how the data is stored on the CD. The earliest file system was High Sierra Standard. The ISO 9660format is now the most common format. 15
16. Tracks and Sectors For burning, the first process is to format a blank CD. CD-ROM drive creates a set of concentric rings, called tracks on each side of CD. Tracks are divided into short segments called sectors. Sectors are where data is stored physically. 16 Tracks
17. Writing Methods There are many methods to write a CD. Monosession: Creates a single session on the disc. Multisession: This method lets a CD to be written several times, by creating a 14MB-long table of contents (TOC) de 14Mo for each session. 17
19. Storage Capacity of CD-ROM Storage capacity is the maximum limit of data storage on a CD. A standard compact disc can store 650 MB of data or about 70 minutes of audio. A new generation of compact disc, however, can hold 700 MB of data or 80 minutes of audio. 19
20. Advantages of CD-ROM Large storage space Compactand light Can be manufactured on a large scale 20
22. Summary Compact Disk is a type of optical storage. It holds data through physical marks. Its is played in a CD-Player, and is read at different speeds. Files system is required to write data on CD by different methods. CDs are compact storage devices that can be moved from on place to another easily. There is always a doubt in their durability. 22
