Wednesday, July 27, 2016
Search
  
Most Popular
Essays
Optical Storage
WEB Reviews
Seagate Enterprise Capacity 3.5 V.3 4TB SAS 6Gb/s HDD Review
OCZ Vector 256GB SSD Review @ Custom PC Review
Gigabyte F2A85XM-D3H
NZXT Phantom 630
Auvio Bluetooth Portable Speaker Review
Corsair H90 CPU Cooler Review
BIOSTAR Hi-Fi Z77X (Intel Z77) Motherboard Review
Noctua NH-L9i Cooler Review on Technic3D
Breaking News
Seagate Releases First 2TB M.2 Enterprise SSD
Western Digital Announces First 64 Layer 3D NAND Technology
BlackBerry Unveils The DTEK50 Android Smartphone
Updated Google Maps Highlight Areas of Interest
Crucial Expands The MX300 SSD Line
Amazon To Start Testing Drone Deliveries In The UK Skies
Ritek To Start Bio-testing Optical Discs
Kingston UV400 SSD Released
Home > Essays > Optical Storage

Monday, June 17, 2002
Writing Quality

2. Pits and Lands

Writing Quality - Page 2

- General information about Pits and Lands

An enlarged view on top of a CD shows a picture like this.


Pit structure

In a CD-player, a laser beam with a specific wavelength detects the digital code by determining the lengths of the pits and the lands. Therefore, it is important that the shape of the pits as well as the intervals meet the necessary preconditions. In the pit structure the next basic parameters can be recognized:


Typical pit parameters

Each pit is approximately 0.5 microns wide and 0.83 microns to 3.56 microns long. (Remember that the wavelength of green light is approximately 0.5 micron) Each track is separated from the next track by 1.6 microns. The leading and trailing edge of the pits represent ones and the length of the pits represents the number of zeros. The space between the pits, called lands are also of varying lengths representing only zeros.

The CD laser 'reads' the pit-information by processing the reflected wave signals. The reflection is caused by the aluminium layer of the CD. The laser beam that is focussed on the pit track 'recognizes' the transition between pits and lands.

Thus not the pits or lands itself but the pit edges are responsible for data information. The pits are encoded with Eight-to-Fourteen Modulation (EFM) for greater storage density and Cross-Interleave Reed-Solomon Code (CIRC) for error correction.




Get RSS feed Easy Print E-Mail this Message


 
Home | News | All News | Reviews | Articles | Guides | Download | Expert Area | Forum | Site Info
Site best viewed at 1024x768+ - CDRINFO.COM 1998-2016 - All rights reserved -
Privacy policy - Contact Us .