Cd Rom
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A CD-ROM uses a laser to read encoded digital data represented by pits and lands on an optical disc. The data is read by detecting changes in light reflection patterns from a laser shining on the disc, where a pit or transition from pit to land represents a 1 and the time between is a 0. A CD-ROM can store around 600 MB of data through this binary encoding scheme addressed by minute, second and sector locations on the disc.
Cd Rom
- 1. Physical Organization of CD-ROM Compact Disc - read only memory (write once) Data is encoded and read optically with a laser Can store around 600 MB data Digital data is represented as a series of Pits and Lands. Pit = a little depression, forming a lower level in the track Land = the at part between pits, or the upper levels in the track
- 2. Reading a CD is done by shining a laser at the disc and detecting changing reflections patterns 1 = change in height (land to pit or pit to land) 0 = a ”fixed" amount of time between 1's
- 3. Changes in height in the track are detected as changes of intensity of the reflected light. Note: We cannot have two 1's in a row!
- 4. Comparing CD-ROM with magnetic disks
- 5. CD-ROM addressing and poor Seek performance Addressing 1 second of play time is divided up into 75 sectors. Each sector holds 2KB. 60 Min CD : 60 min x 60 sec/min x 75 sectors/sec = 270,000 sectors = 540,000 KB 540 MB A sector is addressed by : Minute : Second : Sector 16:22:34 16 min, 22 sec, 34th sector