X (writing speed)
Encyclopedia
Original CD-ROM drives could read data at 150 kibibyte
s (150 × 210 bytes) per second. As faster drives were released, the write speeds and read speeds for optical disc
s came to be indicated by manufacturers in terms of a multiple of the speed of the drives originally released to market. Using the notation nX, n is the multiple of the original speed that can be achieved. For example, writing to a CD at 8X will be twice as fast as writing to it at 4X.
Modern Compact Disc
s support a writing speed of 52X and higher, and some modern DVD
s support writing at 16X or higher. It is important to note that the speed of 1X in CD writing is not the same as the speed of 1X when writing to a DVD. When writing to a DVD at 1X, the data is transferred at 1,385 kB/s (1,385,000 bytes per second); in contrast, a CD at 1X is written at 150 KiB (153,600 bytes) of data (CD-ROM Mode 1) per second (KiB/s). Thus, in brief, one X in DVD writing speeds is about 9 times more than one X in CD writing speeds. However, these speeds are not constant, and depend on the type of data written to the disc.
For Blu-ray discs, 1x speed is defined as 36 megabits per second (Mbit/s), which is equal to 4.5 megabyte
s per second (MB/s). However, as the minimum required data transfer rate for Blu-ray movie discs is 54 Mbit/s, the minimum speed for a Blu-ray drive intended for commercial movie playback should be 2X.
Historically, the 1X writing speed is equivalent to the 1X reading speed, which in turn represents the speed at which a media can be entirely read in 74 minutes. Those 74 minutes come from the maximum play time that the Red Book (audio CD standard)
specified for a digital audio CD (CD-DA), although now most recordable CDs can hold 80 minutes.
The DVD and Blu-ray discs have higher capacity, so reading or writing those discs in the same 74 minutes incurs a higher data transfer rate.
software support selection of the speed at which the portable disc is written. However, the option a user chooses only defines the theoretical maximum of disc burning
process. There are other factors that influence the time taken for a disc to be written to:
Kibibyte
The kibibyte is a multiple of the unit byte for quantities of digital information. The binary prefix kibi means 1024; therefore, 1 kibibyte is . The unit symbol for the kibibyte is KiB. The unit was established by the International Electrotechnical Commission in 1999 and has been accepted for use...
s (150 × 210 bytes) per second. As faster drives were released, the write speeds and read speeds for optical disc
Optical disc
In computing and optical disc recording technologies, an optical disc is a flat, usually circular disc which encodes binary data in the form of pits and lands on a special material on one of its flat surfaces...
s came to be indicated by manufacturers in terms of a multiple of the speed of the drives originally released to market. Using the notation nX, n is the multiple of the original speed that can be achieved. For example, writing to a CD at 8X will be twice as fast as writing to it at 4X.
CD, DVD and Blu-ray writing speeds
| Medium | 1X speed | Capacity (GB) |
Full Read Time (min) |
||
|---|---|---|---|---|---|
| Mbit/s | kB/s | KiB/s | |||
| CD | 1.229 | 153.6 | 150.0 | 0.734 | 80 |
| DVD DVD A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions.... |
11.080 | 1,385.0 | 1,352.5 | 4.7 | 57 |
| Blu-ray Disc Blu-ray Disc Blu-ray Disc is an optical disc storage medium designed to supersede the DVD format. The plastic disc is 120 mm in diameter and 1.2 mm thick, the same size as DVDs and CDs. Blu-ray Discs contain 25 GB per layer, with dual layer discs being the norm for feature-length video discs... |
36.000 | 4,500.0 | 4,394.5 | 25.0 | 93 |
Modern Compact Disc
Compact Disc
The Compact Disc is an optical disc used to store digital data. It was originally developed to store and playback sound recordings exclusively, but later expanded to encompass data storage , write-once audio and data storage , rewritable media , Video Compact Discs , Super Video Compact Discs ,...
s support a writing speed of 52X and higher, and some modern DVD
DVD
A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....
s support writing at 16X or higher. It is important to note that the speed of 1X in CD writing is not the same as the speed of 1X when writing to a DVD. When writing to a DVD at 1X, the data is transferred at 1,385 kB/s (1,385,000 bytes per second); in contrast, a CD at 1X is written at 150 KiB (153,600 bytes) of data (CD-ROM Mode 1) per second (KiB/s). Thus, in brief, one X in DVD writing speeds is about 9 times more than one X in CD writing speeds. However, these speeds are not constant, and depend on the type of data written to the disc.
For Blu-ray discs, 1x speed is defined as 36 megabits per second (Mbit/s), which is equal to 4.5 megabyte
Megabyte
The megabyte is a multiple of the unit byte for digital information storage or transmission with two different values depending on context: bytes generally for computer memory; and one million bytes generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000...
s per second (MB/s). However, as the minimum required data transfer rate for Blu-ray movie discs is 54 Mbit/s, the minimum speed for a Blu-ray drive intended for commercial movie playback should be 2X.
Historically, the 1X writing speed is equivalent to the 1X reading speed, which in turn represents the speed at which a media can be entirely read in 74 minutes. Those 74 minutes come from the maximum play time that the Red Book (audio CD standard)
Red Book (audio CD standard)
Red Book is the standard for audio CDs . It is named after one of the Rainbow Books, a series of books that contain the technical specifications for all CD and CD-ROM formats.The first edition of the Red Book was released in 1980 by Philips and Sony; it was adopted by the Digital Audio Disc...
specified for a digital audio CD (CD-DA), although now most recordable CDs can hold 80 minutes.
The DVD and Blu-ray discs have higher capacity, so reading or writing those discs in the same 74 minutes incurs a higher data transfer rate.
Theoretical versus practical writing speed
Almost all of the modern CD/DVD burningOptical disc authoring
Optical disc authoring, including DVD and Blu-ray Disc authoring , is the process of assembling source material—video, audio or other data—into the proper logical volume format to then be recorded onto an optical disc .-Process:To burn an optical disc, one usually first creates an...
software support selection of the speed at which the portable disc is written. However, the option a user chooses only defines the theoretical maximum of disc burning
Optical disc authoring
Optical disc authoring, including DVD and Blu-ray Disc authoring , is the process of assembling source material—video, audio or other data—into the proper logical volume format to then be recorded onto an optical disc .-Process:To burn an optical disc, one usually first creates an...
process. There are other factors that influence the time taken for a disc to be written to:
- Resources available to the program: Reading or writing data on a disc consumes moderate to high level of system resources (including memory and CPU resources), and running other programs at the same time may force the CD/DVD driveOptical disc recorderIn computing, an optical disc drive is a disk drive that uses laser light or electromagnetic waves near the light spectrum as part of the process of reading or writing data to or from optical discs. Some drives can only read from discs, but recent drives are commonly both readers and recorders,...
to choose a lower speed automatically, to accommodate with the available resources. - Disc quality: Optical disc recorderOptical disc recorderIn computing, an optical disc drive is a disk drive that uses laser light or electromagnetic waves near the light spectrum as part of the process of reading or writing data to or from optical discs. Some drives can only read from discs, but recent drives are commonly both readers and recorders,...
s detect the available speed options based on the data which is available on the disc itself; however, some low quality discs make a high speed option available to the software, while the burning process can never reach that speed in practice. - The reading and writing process does not happen at a steady speed. Both CD and DVD store data with constant linear velocityConstant linear velocityIn optical storage, constant linear velocity is a qualifier for the rated speed of an optical disc drive, and may also be applied to the writing speed of recordable discs. CLV implies that the angular velocity varies during an operation, as contrasted with CAV modes...
, so outer tracks contain more data per radian than inner tracks. During reading and writing, data flow speed varies based on the position of the laser under the disc.
Choosing the best writing speed
Choosing a higher writing speed will result in a faster disc burn, but the optical quality may be lower (less reflective). If the reflectivity is too low to be accurately read when the CD is played back, it may skip or contain unwanted audio artifacts such as squeaking and clicking sounds. For optimal results burn at the media's rated speed.Other media
Removable flash based storage is often rated in ratio to standard CD space. For example, a 100X flash card claims to be able to sustain 100 * 154 kB/s or 15.4 MB/s (100 * 150 KiB/s or 14.6 MiB/s). Read and write speeds will usually have different X ratings.See also
- Reading (technical)Reading (technical)Reading is an action performed by computers, to acquire data from a source and place it into their volatile memory for processing. For example, a computer may read information off a floppy disk and store it in random access memory to be placed on the hard drive to be processed at a future date...
- Optical disc drive
- Data rate unitsData rate unitsIn telecommunications, bit rate or data transfer rate is the average number of bits, characters, or blocks per unit time passing between equipment in a data transmission system. This is typically measured in multiples of the unit bit per second or byte per second.- Avoiding confusion :To be as...
- Optical disc authoring program
- List of optical disc authoring software