Once again, Netflix has rewritten the rules — this time, of the online movie-rental game. The company has done away with expiration dates, copy protection and multi-megabyte downloads. That’s because you don’t actually download any of Netflix’s movies; instead, they “stream” in real time from the Internet to your computer. (This advantage comes with a key disadvantage: you must be connected to the Internet. Wireless hot spots at airports and hotels are fair game, but movies can’t be carried around on a laptop.)

Netflix has also done away with per-movie fees — in fact, there are no additional fees for watching movies online at all. Instead, the Netflix service is free if you’re already a Netflix DVD-by-mail subscriber. When you log in to Netflix.com, you see a new tab called Watch Now. It opens what looks like a duplicate set of the company’s usual excellent movie-finding and movie-recommending tools, except that you now see two buttons beneath each movie’s icon: Rent and Play.

(If you don’t see the Watch Now tab yet, it’s because Netflix is rolling out this service in phases to 250,000 customers at a time, to be completed by June. The idea is to avoid a technical meltdown. Your time will come.)

The first time you click Play, you’re sent a tiny software blob that takes under a minute to install, and doesn’t require restarting your browser or PC. After that, when you click Play, the movie loads for a few seconds and then begins playing, right there in your Web browser. That’s it: one click. No special program, no confirmation boxes, no credit card charges, no copy-protection hassles. The movie just begins to play — full-screen, if you wish. You can jump to any spot in the movie, although the movie takes a few seconds to “catch up” each time you use the scroll bar.

Even more startling: Your movie watching is measured by time, not by individual movie title or by individual viewing.

Image A Netflix screen that lets members watch movies instantly on their PCs. The rollout is scheduled to be complete by June.

The hours of movie watching you get each month depends on which DVD-by-mail plan you have. You get one hour of online movies per dollar of your monthly fee. So if you pay $6 a month (for the one-DVD-at-a-time plan), you can watch six hours of movies online; if you pay $18 (for the three-DVD plan), you can gorge yourself on 18 hours of online movies. And so on.