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CDs vs. DVDs

Friday, August 17th, 2007 by | Filed Under: Multimedia
 
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Q:
Can you please explain the difference between CDs and DVDs? And how about their ROM drives? Are they really all that different?

A:
I sure can and yes, they are! There seems to be a lot of confusion when it comes to these two types of media. These days, most computers come with both a CD ROM drive and a DVD ROM drive and because of that, I think a lot of people assume that you can use either drive for either type of disk. Well, that’s just not the case. Yes, the drives are the same size and shape, but that’s where their similarities end. Let’s check out some of these differences and get all of this cleared up, shall we? Here we go!

For starters (and this is the biggest difference), DVDs have seven times the capacity that CDs do. If you’re not sure, that’s quite a bit! Now, I know you’re probably thinking, “How can that be possible?” Well, DVDs use more layers than CDs and the way DVDs are written is quite different as well, which is a huge booster for the DVD’s capacity size.

Now it’s time for a little background information. CDs and DVDs both store their data in little grooves that run all around the disk. Our CD and DVD ROM drives then scan those grooves with a laser beam, which is how we’re able to listen to music or watch a movie on our computers. They both also work with lands (reflective bumps) and pits (non-reflective holes), which help to represent the digital information the CDs and DVDs need in order to work.

With that said, DVDs work with much smaller pits than CDs. Basically, the smaller the pits, the more data you can fit onto the disk and that’s how DVDs overcome CDs in terms of available space. As a matter of fact, the normal pit length for a DVD layer is 0.4 and for a CD, it’s 0.834. Also, the tracks along a DVD are a lot closer together than on a CD, so that allows for more tracks per disk. As you can see, all of this information runs together to give a DVD a lot more room than is allotted on a CD.

This is also where the biggest difference between the CD and DVD ROM drives comes into play. Because DVDs work with such smaller pits, etc., they need a special drive that will be able to read them. Therefore, a DVD ROM drive cannot read a CD and vice versa (a CD ROM drive cannot read a DVD). That is why most computers these days are coming with both drives already installed. So, while it may seem a little wasteful, now you know why it’s necessary!

Want to know some more differences? Well, like I said earlier, the layer sizes for CDs and DVDs are quite different as well. Along with DVDs having several more layers than CDs, they’re also much thinner. This helps when the laser beam inside the drive is reading the DVD. DVDs also come with double sided layers, which obviously, allow for more information all the way around.

Another big difference is that DVDs can access data a lot faster than CDs can. They also have a better error correction method. And one last difference is the recording format these two types of media use. DVDs record using the Universal Data Format (UDF) method and CDs are not compatible with that type at all. The UDF format allows DVDs to store data, video, audio or a mix of all three onto a single file structure. That file can then be accessed by any drive or computer. CDs just can’t say the same.

Now, I know it may sound like DVDs are the best option when it comes to certain things, but don’t forget that there are times when a CD is just what you need. Sometimes DVDs are just too much and a simple CD will do. Either way, these two media formats are very convenient and handy for all of our recording needs. You have to give props to both of them for all they do!

~ Erin

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