I got a note from downtown saying, "Lots of people were buying (Blu-ray) in the stores today...But we don't really know what it IS."

Blu-ray video discs play high-quality movies (1080p) on high-definition TVs. Compared to regular DVDs, a Blu-ray disc's capacity is huge, even though both are physically the same size: 50 gigabytes, roughly six to ten times more than DVD capacities.

Their manufacture uses a blue laser (hence the name; DVDs use red) whose shorter wavelength can make many more "dots" (think pixels), so more information can be stored on the disc. Hi-def movie files are seven or eight times larger than regular movies, so this capacity is important.

Blu-ray (Wikipedia overview) won the format war -- not VHS v. Betamax but Sony's Blu-ray v.Toshiba's HD DVD -- for optical disc storage when Wal-Mart opted for Blu-ray in February over HD DVD, which Wikipedia now calls an "obsolete high-density optical disc".

So do you have to buy a Blu-ray player if you want to buy or rent high-def DVDs for your high-def TV? Yes. But the reverse is not true.

Walter Mossberg at WSJ wrote, just before the Wal-Mart decision,

I never saw any significant quality difference between the two high-definition formats, I never recommended one over the other. But most of the major studios have defected to Blu-ray, so industry experts believe HD DVD is likely to recede as a movie format, though it may find a market as a data format for computers. However, the companies backing HD DVD haven't given up, so the battle isn't formally over.

Meanwhile, I have found that, for everyone but videophiles, "upscaling" DVD players are effective at making most regular DVDs look better on high-definition TV sets. And name-brand models can be found for as little as $45, which is less than Blu-ray players are likely to commonly cost for quite awhile.

Blu-ray disc players at Amazon start around $200. (They play your old DVDs.) Blu-ray movies are more expensive than DVDs (16.99 vs. $12.99 at Amazon for Indiana Jones and the Crystal Skull, for instance).

All hardware becomes obsolete, and at some point you'll want to upgrade, if you're still using hard media at all. Eventually, prices will drop and newer titles will be hard to find in the older format. But not yet.

Grinch Kyle Buckley at tech-help site Nillabyte (Blu-ray Is Overrated):

When you watch a movie being played from a Blu-ray disc and a DVD side-by-side, you will definitely notice that Blu-ray has a much sharper image. However, the added lines of resolution in Blu-ray are hardly worth upgrading your entertainment system. The number of movies available in Blu-ray format, although growing, is still pretty small....

Background: Reuters reported in February (Wal-Mart picks Blu-ray in HD DVD disaster),

Wal-Mart, the world's largest retailer, announced the move as a phase-out at 4,000 U.S. Wal-Mart and Sam's Club stores by June, saying it was responding to consumer preference.

Wal-mart's on-staff movie and gaming blogger put the future of HD DVD in stark terms.

"So ... if you bought the HD player like me, I'd retire it to the bedroom, kid's playroom, or give it to your parents to play their John Wayne standard def movies, and make space for a BD (Blu-ray disc) player for your awesome Hi Def experience," Wal-Mart blogger Susan Chronister wrote in a posting.

Consumer electronics chain Best Buy Co Inc and online video rental company Netflix Inc defected to the Blu-ray camp earlier in the week.