DVD
| Type: | Optical storage media |
| Introduced: | 1995 |
| Active: | Yes [2010] |
| Cessation: | - |
| Capacity: | 1.4-17 GB (although 17 GB disk is very rare. Common large capacity is 9.4 GB) |
| Compatibility: | DVDs come in two formats: DVD- and DVD+ and neither are universally compatible with disk drives. Some DVD players will only read the same format disks, though DVD writers that only write DVD+R/RW disks will read DVD-R disks. Dual format drives are available which are compatible with both formats. |
| Users: | Broad. Its larger capacity means it is often favoured over CDs for large data file storage. It is also the medium of choice for watching audio visual material, having superseded VHS video cassettes. |
| File Systems: | UDF, ISO9660, HFS/+ |
| Common Manufacturers: | Maxell, Philips, Sony, Verbatim, Memorex |
Recognition
DVDs come in two sizes: standard 12cm and 8cm ‘mini-DVD’. As with CDs, these are often clearly marked with the manufacturer and disk type. However, unlike CDs if you put a DVD into a computer disk drive and select ‘Properties’ the window that opens will state not only that it is a DVD, but will also identify the DVD type (i.e. DVD-RW).
The capacity of a DVD varies quite widely and this is due to its construction. Similar to floppy disks, DVDs can be either single or double sided (SS or DS) and can also be single or double layered (SL or DL). This information is not recorded on a disk, but the disk capacity which is shown does suggest how the disk is constructed. The table below shows the different capacities for a standard sized CD. Be aware that DS DL disks are very rare.
| Construction | Capacity |
| Single Sided and Single Layered (SS SL) | 4.7 KB |
| Single Sided and Double Layered (SS DL) | 8.5 KB |
| Double Sided and Single Layered (DS SL) | 9.4 KB |
| Double Sided and Double Layered (DS DL) | 17 KB |
The capacities for miniDVDs are:
| Construction | Capacity |
| Single Sided and Single Layered (SS SL) | 1.46 KB |
| Single Sided and Double Layered (SS DL) | 2.66 KB |
| Double Sided and Single Layered (DS SL) | 2.92 KB |
| Double Sided and Double Layered (DS DL) | 5.32 KB |
DVDs also vary in writing speed. Original DVDs were 1x, which means they wrote 1,318 KB/s. This translates to 61 minutes for single layered DVDs and 107 minutes for dual layer. Currently DVD speeds increase by multiples of two up to 24x, with the omission of 14x. There is also 2.4x and 2.6x and speeds available depend on the DVD format. These variations affect writing speed and do not impact on any other aspect of a DVD.
Unlike compact disks, there is no single standardised recordable format for DVDs. Instead two formats are competing for the greater market share: DVD- and DVD+. There is little difference between the two in terms of manufacture and performance. The biggest issue is compatibility as not all DVD- disks work with DVD+ drives and vice versa. In July 2003 the hardware website cdrinfo.com produced a comprehensive compatibility test for the different DVD recording formats which concluded that DVD- is the most compatible (compatible with 92.21% of DVD players and drives). A full list of results, including compatibility results for individual DVD players can be found on the website http://www.cdrinfo.com/Sections/DVDMediaFormats/
DVD Formats
This table lists the different DVD formats and the years they were introduced. DL stands for Double Layer.
| Format | Year Introduced | Features |
| DVD-R | 1997 | Write once media |
| DVD+RW | 1997 | Rewriteable media |
| DVD-RW | 1999 | Rewriteable media |
| DVD+R | 2002 | Write once media |
| DVD+R DL | 2003 | Write once, dual layer media |
| DVD-R DL | 2005 | Write once, dual layer media |
| DVD+RW DL | 2006 | Rewriteable, dual layer media |
| DVD-RW DL | 2007 | Rewriteable, dual layer media |
High Definition DVD (HD DVD)
| Type: | Optical storage media |
| Introduced: | 2006 |
| Active: | Only by existing users |
| Cessation: | Format abandoned in 2008 |
| Capacity: | Standard size disk capacity ranges from 15-60 GB (although 60 GB disk is very rare. Common large capacity is 30 GB). Mini-HD DVD capacity ranges from 4.7-18.8 GB. |
| Compatibility: | A HD DVD player or drive is required. |
| Users: | Limited. Used as data storage, particularly video, but small lifespan means it did not establish a large user base. |
| File Systems: | UDF, ISO9660 |
| Common Manufacturers: | Toshiba |
Recognition
As with standard DVDs, HD DVD come in the 12cm and 8cm size and look identical to other DVDs, save for any labelling. HD DVD was indented to be the successor to standard DVDs with its increased capacity of 30GB. However, HD DVDs were in direct competition with blu-ray disks, another high density optical disk. Blu-ray proved to be the more popular choice and the HD DVD format was abandoned by creators Toshiba in 2008.
Again, like standard DVDs, an HD DVD capacity depends on its construction and DS DL HD DVDs are also rare like similar standard DVDs.
| Construction | Capacity |
| Single Sided and Single Layered (SS SL) | 15 KB |
| Single Sided and Double Layered (SS DL) | 30 KB |
| Double Sided and Single Layered (DS SL) | 30 KB |
| Double Sided and Double Layered (DS DL) | 60 KB |
The capacities for miniDVDs are:
| Construction | Capacity |
| Single Sided and Single Layered (SS SL) | 4.7 KB |
| Single Sided and Double Layered (SS DL) | 9.4 KB |
| Double Sided and Single Layered (DS SL) | 9.4 KB |
| Double Sided and Double Layered (DS DL) | 18.8 KB |
HD DVDs are only available in two speeds. The original speed writes data to the disk at a rate of 4.5 MB/s. 2x writes data at a rate of 9 MB/s.
Blu-ray Disks
| Type: | Optical storage media |
| Introduced: | 2002 |
| Active: | Yes [2010] |
| Cessation: | - |
| Capacity: | 7.5-50 GB |
| Compatibility: | Blu-ray disks only work in Blu-ray disk players, which at the time of writing [2010] are inbuilt on some modern computers, but these do not dominate the market. |
| Users: | Mainly used for high-definition video (pre-pressed films) and video games (e.g. Playstation 3). This is still a relatively new technology and has not yet had much impact on the data storage market. |
| File Systems: | UDF, ISO9660 |
| Common Manufacturers: | Sony, Mitsubishi, Philips, |
Recognition
Blu-ray disks look identical to CDs and DVDs and like them come in 12 and 8cm sizes, both of which come in recordable (BD-R) and rewritable (BD-RE) formats.
| Size | Single Layer Capacity | Dual Layer Capacity |
| Standard Blu-ray (12cm) | 25 GB | 50 GB |
| Mini-Blu-ray (8cm) | 7.8 GB | 15.6 GB |
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