In computer jargon, the speed at which data is written to (or read from) an optical disc
(like a CD or a DVD) is shown as a multiple of X. For example, writing to a DVD at 8X will
be much faster than writing to it at 4X.
the writing speed of CD, DVD, Blu-ray
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Modern Compact Discs support a writing speed of 52X and higher, and some modern DVDs
support writing at 16X or higher. It is important to notice 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 a speed of approximately 1.32 MB/s (1,385,000 bytes per
second); in contrast, at single speed (1x) a recorder writes 150 KB (153,600 bytes) of data
(CD-ROM Mode 1) per second. 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 disks, 1x speed is defined as 36 megabits per second (Mbit/s), which is equal
to 4.5 megabytes per second (MB/s). However, as the minimum required data transfer rate for
Blu-ray movie disks is 54 Mbit/s, the minimum reading 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 nowadays 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.
Choosing the best writing speed
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Choosing a higher writing speed will result in a faster disc burn, but for audio CDs the
quality will be lower. For optimal results burn at the media’s rated speed.