5. Data is stored on the disc as a series of microscopic indentations (“bumps", with the gaps between them referred to as "lands"). HOW DATA IS STORED ON A DISC BUMPS ON A SECTION OF A CD 06/07/09 AMRIT BRAR
7. CD-ROM discs are read using CD-ROM drives, which are now almost universal on personal computers. A CD-ROM drive may be connected to the computer via an IDE (ATA), SCSI, S-ATA, Firewire, or USB interface or a proprietary interface, such as the Panasonic CD interface . Virtually all modern CD-ROM drives can also play audio CDs as well as Video CDs and other data standards when used in conjunction with the right software 06/07/09 AMRIT BRAR CD-ROM drives
10. 06/07/09 AMRIT BRAR Laser and Optics CD-ROM drives employ a near-infrared 780 nm laser diode. The laser beam is directed onto the disc via an opto-electronic tracking module, which then detects whether the beam has been reflected or scattered.
11. The fundamental job of the CD player is to focus the laser on the track of bumps. The laser beam passes through the polycarbonate layer, reflects off the aluminum layer and hits an opto-electronic device that detects changes in light. The bumps reflect light differently than the "lands" (the rest of the aluminum layer), and the opto-electronic sensor detects that change in reflectivity. The electronics in the drive interpret the changes in reflectivity in order to read the bits that make up the bytes. 06/07/09 AMRIT BRAR HOW CD PLAYER WORKS?
14. 06/07/09 AMRIT BRAR The rate at which CD-ROM drives can transfer data from the disc is gauged by a speed factor relative to music CDs: 1x or 1-speed which gives a data transfer rate of 150 kilobytes per second in the most common data format. By increasing the speed at which the disc is spun, data can be transferred at greater rates. For example, a CD-ROM drive that can read at 8x speed spins the disc at up to 4000 rpm, giving a transfer rate of 1.2 megabytes per second . Above 12x speed, vibration and heat can become a problem. TRANSFER RATE
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