Optical Media Types - Page 2

The DVD

The invention of the CD certainly turned the computing world around, while previously floppy disks with small capacities were being used to distribute information, and music was all on cassette. The CD brought a universal media that could be used on many piece of hardware. The trouble with the CD though was that not long after it was the accepted media for computers and for music, technology had moved on to the point that more data had to be stored, music was no longer enough people wanted video on a disc format. Software programs were also a lot bigger. The CD could only hold around 650Mb of data, plenty in the past but now not always adequate.

in 1995 the DVD was born, the DVD has the same physical dimensions as the CD but the tracks were much denser and can store up to 6 mines more data than the standard CD format. The DVD commonly referred to as the Digital Versatile Disc (although this has never been defined, its simply the popular choice) was brought into play mainly to store and distribute video on a better and easier platform than the video cassette. Of course the DVD is also able to store data and became the upgrade to the CD-ROM, CD-R and CD-RW. The home PC now had an optical media storage disc that could hold enough information to have large programs on or create decent sized backups.

As DVD technology progressed it became obvious that it had a lot more flexibility than the CD, more types of DVD were produced than ever made it to the shelves with the CD. Competing formats came and went, and some stood the test of time. Now however even the most popular formats of recordable DVD's are not fully supported by all DVD players either stand alone or computer based DVD drives. Now we will look at the formats that are still around and what the differences are between them.

DVD Media

Abbreviation	Full Version	Notes
DVD-ROM	Digital Versatile Disc - Read Only Memory	Similar to the CD-ROM, the DVD-ROM is a WORM (Write Once Read Many) format. Used for hard copies of data and video formats. DVD-ROM's cannot be altered or extra data added to them. The discs used in this format however are compatible with virtually all DVD players and drives. They also have the longest life span of any of the DVD media types.
DVD-R	Digital Versatile Disc - Recordable (Hyphen)	The DVD-R was the first recordable format of the DVD, like the CD-R and recordable layer is added to a DVD that can be "burned" by a laser in a home DVD writer. The capacity of the DVD-R is 4.71GB. This format is DVD (hyphen) R and not what is commonly referred to as DVD (minus) R.
DVD+R	Digital Versatile Disc - Recordable (Plus)	DVD+R is a competing optical media to the DVD-R format. The two are not compatible with each other as they use completely different writing methods and thus are needed to be read differently. Since the DVD+R format is the newest it stands to reason that older DVD players would struggle with this format. But DVD players since around 2004/2005 and most DVD writers are capable of reading both formats of Write Once DVD media. Opinion is split on the matter of DVD-R against DVD+R but techies I think are edging on the side of the DVD+R format as this article at cdfreaks shows
DVD-RAM	Digital Versatile Disc - Random Access Memory	DVD-RAM is the optical media's version of the hard disk. It stores its data in blocks in the same way and requires no special software to be able to use it on a PC. From Windows XP onwards DVD-RAM discs and drives can be used without any further driver requirements. DVD-RAM is a re-recordable format, data can be written to and erased with ease. It is consider a superior format over DVD-RW or DVD+RW because of its built in error control and the ability to be re-written up to 100,000 times. The estimated life of a DVD-RW or DVD+RW is around 1,000 times. While DVD-RAM is available for the home PC it has more of a place in camcorders due to its life-span of 100,000 writes. This makes it perfect for on camera editing. The disadvantage of DVD-RAM will always be its price. It will never be as cheap as the competing Re-Writable formats.
DVD-RW	Digital Versatile Disc - Re-Writable (Hyphen)	Like the CD-RW format, DVD-RW is a Re-Writable format. It is based on the Write Once DVD-R but has a phase change alloy added to it in order for data to be written and the erased of the disc with a laser pulse. DVD-RW have the same capacity as the DVD-R (4.7GB). Again like the CD-RW its life is estimated for around 1000 writes.
DVD+RW	Digital Versatile Disc - Re-Writable (Plus)	The DVD+RW is based on the DVD+R format and also has the phase change alloy added in order to allow changes to made to the data on the disc. the RW disc are less used than the Write Once permanent optical media's because of there price, however they are excellent at providing a media for ever changing data and can be used like a small portable hard disk without the hassle. It is thought that over 3 quarters of all DVD players can now read the DVD+RW format. Most Support both the DVD+RW and DVD-RW formats. These drives are often shown as DVD±RW

Single and Dual Layer

The DVD format was extended to include a Dual Layer effectively doubling the capacity of the recordable DVD, these discs have a capacity of 8.5GB. Dual layer discs are recognised by adding DL to the end of the format e.g. DVD-RW DL. SL stands for Single Layer but is not often added as its taken as always a single layered disc if nothing else is stated. Dual layered disc are created by having a second recording layer on top of the original.

Compatibility is a small issue with dual layered discs. older DVD-ROM drives have problems reading the data as well as some older stand alone DVD players. but this is improving all the time as dual layered DVD's especially for films are becoming more popular. Writing to DVD+/-R(W) DL discs can only be achieved using Dual layer compatible writers.

One side effect of Dual Layer DVD's comes from the DVD's containing films. When he DVD player switches layers it causes a noticeable pause. Many people thought their discs were faulty but this is not the case just an unfortunate side effect of the extra capacity discs a problem that could be resolved with invention of Blu-Ray (next page)

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