The future

Standard DVD players create a digital signal by bouncing red lasers off a pattern of microscopic divots on the disc.

Next-generation formats use blue-violet lasers, which have a shorter wavelength and can read smaller and more densely packed data pits, allowing for greater storage capacity.

Single-layer, single-sided HD DVDs can hold 15 gigabytes, whereas single-layer Blu-ray discs hold 25 gigabytes. Manufactures can add additional layers to increase capacity, and Blu-ray discs could theoretically hold hundreds of gigabytes, according to the Blu-ray Disc Association.

Players for both formats will play DVDs, and many “upconvert” the picture to look better on HDTV.

Some new HD DVDs also have two sides: one standard DVD that works in older players and one HD DVD.