DVD drive/disc physical formats
There are a variety of DVD drive types, each of which requires a specific DVD disc format. A given DVD disc can only be one physical format. It cannot be half DVD-R and half DVD-RAM. You either buy a blank DVD-R disc or a blank DVD-RAM disc.
The physical formats are ...
This is DVD's high capacity read only equivalent to CD-ROM. A DVD-ROM drive will read DVD-ROM, DVD-R and DVD-RW discs and if its a "combi" drive it will also read CD-ROM, CD-R and CD-RW discs.
When you buy an interactive encyclopedia, a game or a piece of software that comes on a DVD disc, you will have bought a DVD-ROM disc.
This is DVDs high capacity write once, read many equivalent to CD-R. A DVD-R drive will read DVD-ROM, DVD-R and DVD-RW discs and if it's a "combi" drive it will also read CD-ROM, CD-R and CD-RW discs.
There are 2 types of DVD-R disc. DVD-R General are suitable for computer/home DVD-R drives, whilst DVD-R Authoring discs are used by professional DVD-R drives.
DVD-R does not support multiple sessions. Discs must be written in one go (disc-at-once).
This is DVDs high capacity write many (up to 1,000 times), read many equivalent to CD-RW. A DVD-RW drive will read DVD-ROM, DVD-R and DVD-RW discs and if it's a "combi" drive it will also read CD-ROM, CD-R and CD-RW discs.
DVD-RW does not support multiple sessions. Discs must be written in one go (disc-at-once).
WARNING: DVD-RW discs do NOT always playback in domestic DVD video players.
DVD-RAM functions like a removable hard disk (Iomega etc). It allows multiple sessions.
WARNING: DVD-RAM discs will NOT playback in domestic DVD video players and so are unsuitable for DVD-video disc authoring.
DVD-R+ and DVD-RW+
DVD+ discs are similar to DVD-R and DVD-RW but record data differently and are not compatible with DVD-R and DVD-RW drives.
A note on Apple superdrives
Apple have been using Pioneer DVD-R/DVD-RW drives in their computers (Apple call them SuperDrives). These drives can only be used with DVD-R and DVD-RW discs.
It is a good idea to use DVD-R discs for publishing finished DVD-video discs, and DVD-RW for testing (discs can be re-written if authoring problems are present) and computer file data backup and archiving.
DVD and computer storage conventions
Confusingly, DVDs and computers define kilobytes, megabytes and gigabytes differently ...
|Byte =||8 bits||8 bits|
|Kilobyte =||1000 bytes||1024 bytes|
|Megabyte =||1000 kilobytes||1024 kilobytes|
|Gigabyte =||1000 megabytes||1024 megabytes|
DVD disc capacities
The DVD specification allows for different disc capacities. For example, at present the capacity of DVD-R and DVD-RW discs is 4.37computer Gb's. As drive specifications improve it is likely that there will be DVD-R and DVD-RW discs with 7.95 and 8.75Gb capacity in the near future.
The main disc capacities are listed below, with CDROM capacity for comparison ...
|Format||Layers & sides||Capacity||Notes|
|CDROM||700 computer megabytes|
|DVD-5 (DVD-R)||single layer/single sided||4.37computer gigabytes, or 4.7 DVD gigabytes, or 4,700,000,000 bytes capacity!||These are used by DVD-R drives such as those found in computers. A 4.37computer Gb DVD disc will hold an average of 2 hours of video at the typical video rate of 2Gbs per hour|
|DVD-9||dual layer/single sided,||7.95 computer gigabytes or 8.54 DVD gigabytes or 8,540,000,000 bytes||Commercially produced discs are often dual layer, permitting 7.95computer gigabytes of data. This allows for a film plus various extras|
|DVD-10||single layer/double sided||8.75 computer gigabytes or 9.4 DVD gigabytes or 9,400,000,000 bytes|
|DVD-18||dual layer/double sided||15.9 computer gigabytes or 17.08 DVD gigabytes or 17,080,000,000 bytes|
Because of the finer tolerances of the DVD laser and disc it is NOT recommended to stick a paper label on a DVD disc. Information can be printed straight onto an inkjet printable disc using a special DVD printer.
DVD disc data formats
Data format refers to the type of data that a disc holds. For example, if you archive computer files to a DVD-R or DVD-RW disc it will effectively become a DVD-ROM disc.
The primary data formats are ...
A DVD-ROM disc will hold computer data files. When you buy an interactive encyclopedia, a game or a piece of software that comes on a DVD disc, you will have bought a DVD-ROM disc.
This is the standard DVD-video format used by the DVD player attached to your TV. If you put it into a computers DVD drive you will be able to watch the video it contains on your screen (providing your computer has the necessary DVD decoder hardware). If you examine the disc in Windows Explorer or the Macs Finder you will find 2 folders entitled "video_ts" and "audio_ts" but you won't be able to do much with them.
The hybrid DVD format allows a mix of DVD-video and DVD-ROM on a single disc.
DVD-audio is designed to replace CD audio disks and offers higher capacity, better quality (24bit, 192KHz) and multi channel surround sound.