What is Blu-ray disc?

At this point, even if you're asking this question, I'm going to assume you know what a Blu-ray disc is. Surely, you've heard of Blu-ray. You may have even used them. But you may not really know what Blu-ray is: how it works, why it's different than DVDs, stuff like that.

So, I'm going to try to explain the more technical aspects without getting too techy.



Blu-ray disc is an optical storage disc that holds up to 25GB of data per single-layer disc and up to 50GB per dual layer disc.

The Blu-ray disc got its name from the blue laser that is used to read and write data. The blue laser operates at 405 nm (nanometers). Technically this is in the visible violet spectrum of light, but it is definitely more blue than the red laser used to read/write DVDs, which operates at 650 nm. This blue light, in combination with a high-density objective lens (the part that focuses the laser), is what allows higher density data reading.

On a Blu-ray disc, the tracks are smaller and more densely packed than the tracks on a CD or even a DVD. In fact, the track width on a Blu-ray disc is less than half that of a DVD disc and the laser spot is about 80 percent smaller. Get it? A smaller laser spot means the laser can read data in a smaller area.

So, how small are the tracks? The tracks on a Blu-ray disc are .32 microns (micrometers); a DVD track is .74 microns, a CD is 1.6 microns and a human hair is 100 microns. If you're having trouble visualizing that, the graphic below may help. (Click on the image to see the full-size image.)

Recordable Blu-ray discs (write-once) are also called BD-Rs. There are branded versions (the disc surface has the manufacturer's logo and information) as well as inkjet printable, silkscreen printable, thermal printable and even Smart White BD-R discs, which will work with your current disc printer. However, if you have an all-in-one DVD-R publisher, you can print to the disc surface, but you must record with a Blu-ray recorder or Blu-ray duplicator tower. Blu-ray publishers are also available. (And you can use your EM2B$ toward the purchase of Blu-ray equipment.)

Rewriteable Blu-ray discs (write many) are also called BD-REs.

Aug. 25, 2010 edit: I just found out something new about Blu-ray. According to Microboards, BD-Rs are sector-based, so you can keep writing to it until it's full.  (CDs and DVDs can only be written to once, even if you don't use all the available space.) That's why Blu-ray is such a good archiving tool: you can keep adding to it, but you can't overwrite on the part that was already burned.

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