JV Systems
March TechKnow

Optical Storage Formats - CD and DVD

First there were floppy disks. Easy, but limited capacity. Then CDs. First read only, then write, then re-write. With capacities close to 700MB. Now DVDs. Again, first read only, then write, now rewrite. With capacities close to 16GB storage. Seems quite straight forward. But it’s not. The big issue is formats. We went through all the issues with the CD formats, now again with DVD formats. Which is best? Which will prevail? Impossible to say, but at least we can look at the options.

CD-R Technology

CD-R is a ‘write once’ technology that can be used in both CD-R and CD-RW recorders and read by nearly any computer CD drive or audio CD player.

In a CD-R, the recording layer is made with organic dyes — greenish cyanine dye, golden phthalocyanine dye, or silver-blue azo dye, depending on the disc manufacturer. The laser of your CD-R/CD-RW drive heats the dye to a temperature of about 200° C, irreversibly melting a pitted pattern into the recording layer. A plastic layer alongside the dye expands into the newly available space, creating a pit pattern similar to that of a conventional CD. Your CD player reads this highly reflective pattern for playback. Because the plastic layer melts into the dye layer to set the pattern, CD-R discs cannot be re-recorded.

CD-RW Technology

Unlike CD-R discs, a CD-RW disc can be reused — in fact, up to 1,000 times with current discs and perhaps even more with upcoming media improvements. However, older computer CD drives and audio CD players cannot read CD-RW media.

In a CD-RW disc, the recording layer is made of an alloy of silver and other metals — indium, antimony, and tellurium. Out of the case, this layer has a polycrystalline structure. When you record to the CD-RW, your CD-RW drive's laser selectively heats tiny areas of the recording track to a temperature above the layer's melting point (500 - 700° C) — a much higher heat than the laser in a CD-R recorder can reach.

The energy delivered by the laser beam melts the crystals in the heated areas into a non-crystalline phase — also known as "pits." These pits reflect less light than the remaining crystalline areas, creating the playback pattern for your Multi-Read CD-ROM drive or specialised audio CD player.

Because the recording layer is self-fixing, a CD-RW disc can be erased. A CD-RW recording drive erases a recorded CD-RW by returning the pitted material in the recording layer to a crystalline state. The drive's laser heats the recording layer to a temperature of about 200° C and maintains that temperature for an extended period (more than half an hour for a complete disc, in most cases). The result is a blank disc, ready for reuse.

A recorded CD-RW may also be overwritten, saving time compared to erasing then re-recording. Overwriting combines the recording and erasing procedures. The laser writes a new data pattern to the disk, and also creates new crystallised areas between the newly recorded pits. The beam switches between the higher-energy recording level and the lower-energy erase level, resulting in simultaneous erasure of the old information on the disk and recording of a new track of data.

The complexity of the recording process makes clear why CD-RW technology still costs more than CD-R technology. However, more and more people are finding CD-RW gear to carry more value for the increasingly slim price difference in drive cost, thanks to its versatility and ability to record to both CD-R and CD-RW media.

DVD Formats

With so many different formats — DVD+R, DVD+RW, DVD-RAM, DVD-R, DVD-RW, DVD-ROM — resellers have their hands full understanding the products they sell, much less explaining the finer points to customers. The following information sheds some light on DVD's different flavours, the differences between them and the incompatibility issues that the differing technologies have sprouted.

DVD+R and DVD+RW

DVD+R and DVD+RW formats are supported by Philips, Sony, Hewlett-Packard, Dell, Ricoh, Yamaha and others. DVD+R is a recordable DVD format similar to CD-R. A DVD+R can record data only once and then the data becomes permanent on the disc. The disc can not be recorded onto a second time.

DVD+RW is a re-recordable format similar to CD-RW. The data on a DVD+RW disc can be erased and recorded over numerous times without damaging the medium. DVDs created by a +R/+RW device can be read by most commercial DVD-ROM players.

DVD-R, DVD-RW and DVD-RAM

These formats are supported by Panasonic, Toshiba, Apple Computer, Hitachi, NEC, Pioneer, Samsung and Sharp. DVD-R is a recordable DVD format similar to CD-R and DVD+R. A DVD-R can record data only once and then the data becomes permanent on the disc. The disc cannot be recorded onto a second time. There also are two additional standards for DVD-R disks: DVD-RG for general use and DVD-RA for authoring, which is used for mastering DVD video or data and is not typically available to the general public.

DVD-RW is a re-recordable format similar to CD-RW or DVD+RW. The data on a DVD-RW disc can be erased and recorded over numerous times without damaging the medium. DVDs created by a -R/-RW device can be read by most commercial DVD-ROM players.

DVD-RAM discs can be recorded and erased repeatedly but are compatible only with devices manufactured by the companies that support the DVD-RAM format. DVD-RAM discs are typically housed in cartridges.

DVD+R DL and DVD-R DL

Dual layer technology is supported by a range of manufacturers including Dell, HP, Verbatim, Philips, Sony, Yamaha and others. As the name suggests, dual layer technology provides two individual recordable layers on a single-sided DVD disc. Dual Layer is more commonly called Double Layer in the consumer market, and can be seen written as DVD+R DL or DVD-R DL.

DVD+R DL (also called DVD+R9) is a Dual Layer writeable DVD+R. DVD-R DL (also called DVD-R9) is a Dual Layer writeable DVD-R. The dual layered discs can hold 7.95GB The dual layered discs (DVD+R9 and DVD-R9) can hold 7.95GB and double sided dual layer (called dvd-18) can hold 15.9GB

DVD-ROM

DVD-ROM was the first DVD standard to hit the market and is a read-only format. The video or game content is burned onto the DVD once and the DVD will run on any DVD-ROM-equipped device.

A Note on DVD Burners

Until 2003 consumers would have to choose a preferred DVD format and purchase the DVD media that was compatible with the specific DVD burner. In 2003 the first multi-format DVD burner (also called a combo drive or DVD-Multi) came on the market and today many manufacturers offer multi-format DVD burners which are compatible with multiple DVD formats.

The Next Big Thing?

Two new high-definition videodisc formats, HD DVD and Blu-ray Disc, are starting to compete for the attention of consumers in an effort to replace current DVD as the future standard consumer DVD. Both formats use blue laser technology, which has a shorter wavelength than red, allowing it to read the smaller digital data "spots" packed a lot more densely onto a standard-size disc. HD-DVD is capable of holding 30GB or a full-length high-definition movie, plus extras, on a prerecorded double-layer disc (compare that to today's limit of 9GB for standard double-layer DVDs). Blu-ray will go up to 50GB at launch, and Sony is reportedly working on a quad-layer 100GB disc.

However, the two formats are incompatible and mean that consumers have to make a choice on which one will become the standard. A format war will probably result in consumer confusion and apathy. It’s even possible that a prolonged format war – particularly one with no clear winner – could slow the potential market for high-definition movies on disc.

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