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Writing a DVD at 1× (1 385 000 bytes per second) [5] is approximately 9 times faster than writing a CD at 1× (153 600 bytes per second). [6] However, the actual speeds depend on the type of data being written to the disc. [6] For Blu-ray discs, 1× speed is defined as 36 megabits per second (Mbit/s), which is equal to 4.5 megabytes per second ...
Some high-speed CD and DVD drives can use CAV. [specify] It allows for shorter access times because the rotation speed (angular velocity) does not need to be changed when the laser seeks across the disc, similarly to the magnetic head of a hard disk drive. With a given angular (rotation) speed, the linear speed at the outermost track is nearly ...
If the data density is the same everywhere on the disc, as is the case with CD and DVD and Blu-ray discs, the linear velocity directly correlates with the transfer rate (read speed or write speed), meaning an increase in linear velocity also increases the amount of data read from the disc in the same time, regardless of whether the laser is ...
Although a number of optical formats have been used over time, the most common examples are optical disks like the compact disc (CD) and DVD. Reading and writing methods have also varied over time, but most modern systems as of 2023 [update] use lasers as the light source and use it both for reading and writing to the discs. [ 1 ]
Encoding is done by means of difference in reflectivity of the alloy, a laser is pointed at the surface and the returned intensity signifies either a 1 or a 0. [3] DVD-RAM uses concentric tracks each divided into hard (factory originated) sectors, in contrast to traditional spiral recording found in other DVD and CD formats.
Examples: CD-ROM represents the CD format, in its pre-recorded "read only" use; DVD+R represents a DVD "+" disc which can be written once only; DVD-RW represents a DVD "-" disc which can be read or written many times; BD-RE represents a Blu-ray disc which can be read or written many times.
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Each sector (or "timecode frame") consists of a sequence of channel frames. These frames, when read from the disc, are made of a 24-bit synchronization pattern with the constant sequence 1000-0000-0001-0000-0000-0010, not present anywhere else on the disc, separated by three merging bits, followed by 33 bytes in EFM encoding, each followed by 3 merge bits.