There are many different types of data storage discs, varying in their capacity, physical properties, and how they are read. In this article we will explore three specific types of disks; these are CD, DVD and BD discs. To clear up any misunderstandings, CD stands for compact disc, DVD means digital video disc or digital versatile disc, and BD stands for Blu-ray disc. These discs are all 12 centimeters in diameter with a 15 mm diameter circular hole in the center used to place the disc in the player called a disc drive. General Function: These discs generally work by rotating around their center point, driven by an optical engine, where a laser beam is precisely focused to a point on the reflective side of a disc which is reflected in two ways due to bumps or microscopic cavities (depending on how you look at it) on the inner surface of the disc. These bumps are positioned in a spiral line outward from the central ring to the outside of the disc. Therefore, as the disk spins and the microscopic bumps are read, the laser head slowly moves from the center to the outer edge or from the outer edge inward until the data has been read. Each rotation of the disk, as it follows the spiral, is called a track. A normal CD has approximately 22188 tracks (Kioskea.net (2014)) and has a data capacity of 650 megabytes. A regular DVD has just over 7 times the capacity of a CD which is 4.7 gigabytes and a Blu-ray disc has about 5 times that of a DVD which is 25 gigabytes. The reason Blu-ray discs can hold substantially more data than others is due to their more advanced optical system. The optical system: the standard CD drive contains a laser (amplification of light by stimulated emission of radiation......half of the paper......correct disc to buy for your needs, it is important to know how much space you will need it and if you have the correct hardware to use it Generally you could fit a few dozen songs on a disc A CD whereas on a DVD you could fit an entire movie and on a Blu-ray disc you could fit a complete movie in Full HD plus a little extra. And even then, you might think why not just buy a Blu-ray disc and you'll never run out of space. Well, for starters they cost more and most common disc drives don't even support Blu-rays, the which will cost you a lot more to buy. Therefore, I generally recommend using DVDs as they are cheaper, usually have sufficient storage capacity and it is very likely that if you already have a disc drive, this one would support the use of DVDs and would not require the purchase of the necessary hardware. Refer to Table 7 for buyer comparison of typical discs.