Radschool Association Newsletter

Radschool Association Newsletter - Vol 9

Next reunion - 27 April 2003

20 Jan 2002

Page 6

Computers and stuff

Sam Houliston

This article appeared in a recent C-NET newsletter. We thought it very informative, so we’ve reproduced it here.

To understand why variations in CD-R compatibility and reliability exist (i.e.; why you end up with so many coasters), it helps to know a bit about the makeup of the media. CD-R media has four layers: an upper label/protective layer, a reflective layer, a photo reactive-dye layer, and a transparent plastic (polycarbonate) bottom layer, which protects the two middle layers. Your CD-R/RW drive writes data to these discs by firing a laser in a short burst to burn a hole in the dye layer. This hole is filled in by the metal in the reflective layer above it, which creates a bright spot that's read like a pit in a commercial CD (commercial CDs are pressed much like LPs used to be).

Silver and gold

The fighter pilot's creed: "Speed is life, altitude is insurance."

The reflective and dye layers are the most important layers in the equation. The reflective layer can be gold, silver, or a combination of both. Gold is generally thought of as the most stable in the long run since it's the least reactive with dyes and, therefore, less prone to corrosion. However, there's also a good argument for silver, which was specified in the original standard because it's more reflective and, therefore, more easily read by players. Manufacturers also claim that dye formulas have been improved to the point where reactions with the reflective layer are no longer an issue.

A number of DVD formats are vying for consumers' attention.

DVD-ROM	Read (play) only.
DVD-R	Record once. Movies can be played on most recent consumer DVD players.
DVD-RAM	Record, erase repeatedly. Recorded movies cannot be played on most consumer DVD players. Best used for data storage.
DVD-RW	Record, erase repeatedly. Mainly for movies. Compatible with most recent consumer DVD players.
DVD+RW	Record, erase repeatedly. Data storage or movies. Compatible with most recent consumer DVD players

DVDs can hold 4.7GB of data, about seven times as much as recordable CDs.

The road to video nirvana, though, is paved with potholes. There are three competing standards, DVD+RW, DVD-RW and DVD-RAM, all vying for market supremacy, confusing compatibility issues and keeping prices high. Good luck

Fool's gold

Buying a disc with real gold in it can be a challenge because you can't go simply on product labelling or even the colour of the disc. The packaging on some generic discs may use the word gold strictly as an advertising ploy. And disc colours can be deceptive. The upper layer can be any colour of the rainbow, and manufacturers have also recently taken to colouring the transparent bottom layer. Some discs, for instance, have a gold-coloured upper protective layer, yet they actually use a silver reflective layer.

How can you tell fool's gold from the real thing? If store personnel cannot confirm the truth for you, ask them if you can open a package and look at the disc. If you look very closely at the bottom layer, even through a colour, you should be able to see a warm glow to the disc that signals true gold inside. Comparing a gold disc to a silver disc makes it easier to see the difference. If you cannot perform any of these checks, your best bet is to research company Web sites for the specification, or you can just learn from experience by buying different brands and comparing them.

To dye for.

The photo reactive-dye layer comes in more variations than the reflective layer does. The original official CD standard called for TDK's Azo dye, which is dark blue. However, a number of other dyes, such as the lighter blue cyanine, have been developed and employed since--basically so that vendors don't have to pay each other royalties. Some dyes, such as phthalocyanine, are lighter than others and don't produce as distinct a variation in colour between burn marks and the unburned areas. This has been the traditional knock on common reflective/dye combinations such as gold/phthalocyanine. By and large, however, CD-ROM-drive manufacturers have learned to compensate for the differences in dyes. Some recorders do have more trouble recording on phthalocyanine, but the discs do have a reputation for lasting longer than cyanine ones. Next issue-how to care for your CD’s

Q.	Why are married women heavier than single women?
A.	Single women come home, see what’s in the fridge and go to bed. Married women come home, see what’s in bed and go to the fridge.

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