Blu-ray

Last updated: April 30, 2008.

People forget things all the time, but that doesn't really matter because we have books, computers, CDs, DVDs, and all kinds of other technologies to help us remember. You can store 10,000 thick books on a DVD—which is about seven times more than you can fit on a CD. Imagine that: 10,000 books is about 200 shelves or 6-7 bookcases worth or knowledge. But there's no such thing as too much information. DVDs may be amazing, but sometimes you need to store even more information than they can cope with. So thank goodness for a new kind of disc called Blu-ray, which can store six times more data (digital information) than even the best DVDs—that's a whopping 50 gigabytes worth!

Photo: They're not called Blu-ray discs for nothing but, in other respects, they look just like CDs and DVDs. (This photo has been falsely colored.)

Why Blu-ray can store more information

If you're not sure how optical discs store information, you might want to read our article about CDs and DVDs before you go any further.

Blu-ray discs are exactly the same size as DVDs, which are themselves the same size as CDs. How do Blu-rays store more than DVDs? How do DVDs store more than CDs? The answer is simple. If you've ever had to squeeze a certain amount of text on a single sheet of paper (maybe to make a poster) and found it difficult to get everything on, you'll know there's a simple solution: you just make your words a bit smaller (lower the font size). The same idea works when you're writing computer data on discs with laser beams. You can store more on a DVD than a CD by using a laser beam that "writes smaller". And to read or write a Blu-ray disc, you use a laser to write even smaller still.

Photo: A blue laser (left) and a red laser (right). Photo by National Energy Technology Laboratory, Morgantown courtesy of US Department of Energy.

A DVD uses a red laser beam that makes light waves with a wavelength of 650 nanometers (0.00000065 metres, or less than one hundredth the width of a human hair). That's considerably shorter than the wavelength of invisible, infared light that an CD player uses (780 nanometers), which is why DVDs can store more than CDs. A Blu-ray player uses an even more precise laser than a DVD player, with a beam of blue light shooting out of it instead of red or infrared. Blue light has a much shorter wavelength (about 450 nanometers) than red light so a blue laser can write things that are far smaller. That means Blu-ray discs can store movies in a much higher quality format known as High Definition (HD), store much longer movies on a single disc, or just store more altogether. If you can fit four, half-hour episodes of Friends on a DVD, you can fit 24 episodes (a whole series) on a Blu-ray disc.

With a DVD, you use a red laser beam to read and write the information. The information you write onto the disk can't be smaller than the size of the beam. By using a much finer blue laser beam, Blu-ray can write smaller and store more information in the same space.

Is Blu-ray becoming more popular?

Despite a slow start, Blu-ray discs are beginning to gain in popularity—especially since a rival type of disc, called HD-DVD (High-definition DVD), fell by the wayside in early 2008. Blu-ray players are widely available and powerful games machines like the Sony PlayStation 3 have built in Blu-ray drives. There are already hundreds of Blu-ray discs on the market and thousands more are likely to follow in the next few years.

Blu-ray isn't the end of the story, by any means. It's only a matter of time before cunning engineers develop lasers that can pack even more data on a disc. But whether we'll actually be using discs at all in the future is another matter. Many people are already using their broadband Internet connections to download MP3 music tracks, movies, and TV programs online and it may just be a matter of time before disc players disappear altogether.