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Optical storage media writing and reading speed

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In the history of optical storage media there have been and there are different optical disc formats with different data writing/reading speeds.

Original CD-ROM drives could read data at about 154 kilobytes (153.6 × 103 bytes) per second[citation needed], 1× constant linear velocity (CLV), the same speed of compact disc players without buffering. As faster drives were released, the write speeds and read speeds for optical discs were multiplied by manufacturers, far exceeding the drive speeds originally released onto the market. In order to market increasing drive speeds, manufacturers used the symbol n×, whereby n is the multiple of the original speed. For example, writing to a CD at 8× will be twice as fast as writing onto a disc at 4×.[1]

There are two main types of disc speed, which are the angular and linear velocities. If the disc spins at a constant angular velocity, the linear velocity is 2.4 times higher at the outer edge.

Various optical disc formats writing/reading speeds

Comparison of various optical storage media. Parameters: track pitch (p), pit width (w) and minimum length (l), and laser spot size (⌀) and wavelength (λ).
Media 1× speed Capacity of a single layer (decimal)
 Capacity of a single layer (binary)
 Full read time
(min)[2]
Mbit/s kB/s MB/s
CD 1.229 153.6 0.15 734 MB 700 MiB 80
DVD 11.080 1385.0 1.38 4.7 GB 4.38 GiB 103
HD DVD 36.000 4500.0 4.5 15.0 GB 13.96 GiB 110
Blu-ray 36.000 4500.0 4.5 25.0 GB 23.28 GiB 180

Modern compact discs support a writing speed of 52× and higher, with some modern DVDs supporting speeds of up to 24×.[3] It is important to note that the speed of writing a DVD at 1× (1385000 bytes per second)[4] is approximately 9 times as fast as writing a CD at 1× (153600 bytes per second).[5] However, the actual speeds depend on the type of data being written to the disc.[5]

For Blu-ray discs, 1× speed is defined as 36 megabits per second (Mbit/s), which is equal to 4.5 megabytes per second (MB/s).[6] 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 2×. The fastest Blu-ray speed is 16×. For CDs, the 1× writing speed is equivalent to the 1× reading speed, which in turn represents the speed at which a piece of media can be read in its entirety, 74 minutes. Those 74 minutes come from the maximum playtime that the Red Book (audio CD standard) specifies for a digital audio CD (CD-DA); although now, most recordable CDs can hold 80 minutes worth of data. The DVD and Blu-ray discs hold a higher capacity of data, so reading or writing those discs in the same 74-minute time-frame requires a higher data transfer rate.

As for video games, differences carried other meaning than in the film industry in the late 2000s. Games for PlayStation 3 were stored on single-layer Blu-ray which has a higher data rate per second by default but the console's drive speed multiplier was set at 2× (9 MB/s). On Xbox 360, video games were stored on common dual-layer 8.5 GB DVDs but with the console's 12× drive speed multiplier (16.5 MB/s), Xbox 360 could achieve up to 85% faster data transfer rate than PlayStation 3. Slower transfer rate on PlayStation 3 led many multi-platform developers for a mandatory installation of a portion of the disc's content on the console's hard disk drive in order to compensate for problems such as longer loading times.[7][8][9][10] Xbox 360 could install whole games on hard drive and potentially improve loading times but this was never mandatory.[11] Seventh generation video games rarely filled the space of an entire single-layer Blu-ray disc (25 GB) or required two or more DVDs on Xbox 360.

Theoretical versus practical writing speed

Almost all modern CD/DVD-burning software supports a selection of speeds at which the writable disc can be 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:

  • 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 drive to choose a lower speed automatically, to accommodate the available resources.
  • Disc quality: optical disc recorders 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 may not happen at a steady speed. CD drives and many early DVD drives stored data with constant linear velocity, so that the data rate remained the same regardless of the position of the optical head. Modern DVD drives use constant angular velocity to allow transferring data at the highest supported physical rotation speed and/or random access without needing to adjust the physical rotation speed on every jump, and Zoned Constant Linear Velocity for writing reliably with different data rates in different zones.

Optimal writing speed

A higher writing speed results in a faster disc burn, but the optical quality may be lower (i.e. the disc is less reflective). If the reflectivity is too low for the disc to be read accurately, some parts may be skipped or it may result in unwanted audio artifacts such as squeaking and clicking sounds. For optimal results, it is suggested that a disc be burnt at its rated speed.[12][13]

See also

References

  1. ^ "What is Read Speed? What is Write Speed?". Misco. Archived from the original on October 2, 2011. Retrieved August 26, 2021.
  2. ^ Full read time can be increased, adding more minutes by using compression techniques and lowering content quality.
  3. ^ "Three Generations Compared: Is Your DVD Burner Outdated?". Tom's Hardware. October 30, 2009. Retrieved August 26, 2021.
  4. ^ "Understanding Recordable & Rewritable DVD recording speed". OSTA. Retrieved August 26, 2021.
  5. ^ a b "Understanding CD-R and CD-RW recording speed". OSTA. Retrieved August 26, 2021.
  6. ^ "Blu-ray writing speed". Blu-ray.com. Retrieved August 26, 2021.
  7. ^ "Why some PS3 games need installation". Joystiq. April 2, 2008. Archived from the original on April 5, 2008. Retrieved August 26, 2021.
  8. ^ "The Mystery Behind PlayStation 3's Sometimes Mandatory Installations". MTV. April 1, 2008. Archived from the original on April 5, 2020. Retrieved August 26, 2021. {{cite web}}: |archive-date= / |archive-url= timestamp mismatch; April 5, 2008 suggested (help)
  9. ^ "Capcom addresses DMC4 install complaints". Joystiq. February 5, 2008. Archived from the original on February 7, 2008. Retrieved August 26, 2021.
  10. ^ "GTA IV for PS3 Has Mandatory Install, Xbox 360 Install Is Optional". Softpedia. April 17, 2008. Retrieved August 26, 2021.
  11. ^ "Install, play, or delete a game on your Xbox 360 hard drive". Microsoft. Retrieved August 26, 2021.
  12. ^ Robjohns, Hugh (November 2004). "Why does the speed at which you burn a CD make a difference?". SoundOnSound. Retrieved August 26, 2021.
  13. ^ "Which write speed should I use?". Feurio. Archived from the original on February 1, 2010. Retrieved August 26, 2021.
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