By Columnist
updated 4/20/2006 9:47:07 PM ET 2006-04-21T01:47:07

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 ( and where you can check out their programming. Then ask your friends, family and co-workers which one they like. 

Greg Wayne of Bedminster, N.J., asks:

I am getting into HD Radio listening. What are the best indoor AM and FM antennas that could help me pull in a good digital signal?

Outdoor antennas are always better than indoor ones. I realize some people aren’t allowed to install outdoor antennas because of house rules where they live. But there is nothing better than a large, outdoor metal antenna mounted on the highest point of your building.

Indoor antennas can’t come close. At best, they are a compromise. It’s all based on physics.  A radio wave is broadcast on a certain frequency. The radio wave is a specific length corresponding to that frequency. You need the antenna to be large enough to receive that wave properly. Indoor antennas just aren’t large enough to do the job.

HD radio is broadcast on the FM radio band and it actually needs an even better antenna than plain old FM. If you can swing it, go with an outdoor antenna for the best results.

William Thaxton of Grifton, N.C., wants to know: Where are those HDTV "external tuners" that will be required for all these "monitors" now being sold? When I search the Net I find only two or three units listed (starting at about $250) and I have yet to actually SEE a unit at one of the mass-market outlets. I guess this is OK if you have cable or satellite but those of us that use broadcast TV are kind of stuck.

A lot of the new TVs have HDTV tuners built inside so that you can receive over-the-air high-definition stations right now. If you don't have one, don't worry about when the external ones will come to market. They’ll be there as the deadline to switch over to HDTV gets closer. Expect the prices to drop the closer we get to that date.

Bill York of Raleigh, North Carolina asks: At the moment there are three different types of HDTVs on the market: plasma, LCD and DLP. Is one these formats superior to the others?

A plasma TV has a flat panel display where different intensities of light are created when excited by a (xenon/neon) gas discharge between two flat panels of glass. 

LCD (liquid crystal display) screens use electrical impulses to light-up millions of LCD modules packed into the screen.

DLP stands for Digital Light Processing and is a new technology used in projector TVs.  The DLP image is created by microscopically small mirrors placed in a matrix format on a semiconductor chip. It is a great improvement on older projector TVs.

As for which is the best — that’s difficult to say. 

Plasmas were the first large-format, flat-screen format to hit the market. Plasma displays can develop little dots of white as the screens approach the end of their useful life.

Older LCDs were plagued by the fact that picture contrast wasn’t as good as plasma’s — and that large LCD screens were way too expensive to design and manufacture. These days, contrast has been improved greatly and I’ve seen LCD TVs with screens approaching 100 inches diagonally. (But don’t ask what they cost.)

DLP sets are much brighter than old-fashioned projector TVs. You don’t have to darken a room to watch a DLP projector TV.

My suggestion is do the research and go look at everything in your price range. Go to a few stores and compare these new sets. Make sure you watch the same video on the TVs you’re considering. One way to do this is to carry a favorite DVD with you and ask that it be played. Another is to ask someone at the store to move two TVs next to each other for comparison's sake. If you’re spending a few thousand dollars on a TV you should get some service as well.

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