Slurping an alphabet soup of media formats

Gary Krakow Columnist • E-mail

I use a lot of technical terms when I write my columns. That comes with the territory. ButI sometimes forget that not everyone understands what every one of these terms mean.

So, my first questions are from two readers who are confused, as rightfully so, over the alphabet soup terms for reading and recording computer disks.

Luis of Vista, Calif. asks: Can you explain me what is the difference between all the CD’s? Why they are called CD-R, CD-RW?

Plus, Paul Noel of Union, Kentucky wants to know: Please, please explain the whole +/- DVD writeable thing.

Let's start with Luis' question. Both CD-R and CD-RW are recordable compact discs. What makes them recordable is a "blank" data spiral. In the case of CD-Rs (compact disc-recordable), the laser writer of the CD recording drive alters the spiral’s dye. The change is permanent, so you can only record content once on a CD-R disc. CD-Rs can be read by most computer CD drives and played in most standard audio CD players.

CD-RW (compact disc-rewritable) discs use a metallic alloy instead of a dye. The write laser is used to heat that alloy, changing its reflectivity. Not all CD audio players can read CD-RW discs, but most DVD players can.

Recordable DVDs are even more complicated. They use dyes, just like recordable CDs, but that’s where the similarity ends. There are three major formats: DVD- (that’s a dash), DVD+ (plus) and DVD-RAM (random access memory).

The DVD- format was used by the first recordable DVDs and was developed by Pioneer, based on the CD-R/RW format. Most DVD players can read DVD- disks, but questions of disc reliability have cropped up over the years. A DVD-R disc can only be recorded once (similar to CD-R), but a DVD-RW disc can be recorded over again multiple times (again, similar to CD-RW).

DVD+ was developed by Phillips and Sony as a rival to Pioneer’s DVD- format. You need a DVD+ rated player to play a DVD+ disc, and again, the discs come in both "write once" and "rewritable" formats: DVD+R and DVD+RW.

Still with me?

There are now multi-format drives that are called DVD±RW (DVD plus-dash rewritable) that can write/rewrite both plus and dash formats, but not necessarily DVD-RAM discs.

So, of course, now I have to tell you about DVD-RAM, or DVD-Random Access Memory. The format was developed so that businesses could back-up their big files. Of course, only DVD-RAM compatible drives can read DVD-RAM disks.

Hope that helps.

Rob Whitmore of Roanoke, Virginia asks: Can you explain the main differences between Sirius and XM (satellite radio services)? I hear Sirius uses compressed audio for transmitting their music whereas XM does not. Any major difference between the two?

Without getting into a long-winded explanation, Sirius and XM are very much alike in terms of programs you can listen to and, more importantly, in technical terms. Sure, there are slight differences in the way they "broadcast" the music to you, but that shouldn’t make a big difference to you.

I’ve found XM has a slight edge in sound quality, but neither service can compare to the audio quality of free HD radio on the FM band which is currently being rolled out in major cities. But satellite services can be heard all over the country right now and have hundreds of different channels available. You’ll have to wait for HD Radio to equal that.

A good way to test-drive Sirius and XM is to listen to them online. Both offer free "three-day passes" on their Web sites (www.sirius.com and www.xmradio.com) where you can check out their programming. Then ask your friends, family and co-workers which one they like. 

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