You could say that Windows Vista comes in five editions. You could say that it comes in eight (if you count the overseas versions).

You could also multiply all that, because most Vista versions are also available in either 32-bit or 64-bit editions. (Vista Ultimate comes with both versions in the box; the Business or Home versions come with the 32-bit version, with a toll-free number that lets you order the 64-bit version at no charge.)

Which leaves only one question: What does it all mean? Aren't more bits always better?

Not necessarily.

In theory, there are two advantages to a 64-bit computer running a 64-bit operating system. First, you can install a lot more memory. The most memory you can install on a 32-bit computer is 4 gigabytes of RAM; on a 64-bit computer, the maximum shoots up to 128 gigabytes. (That's for the Business, Enterprise, and Ultimate editions of Vista; it's 8 GB for Home Basic, and 16 GB for Home Premium.)

Second, certain people in certain rarefied professionssay, Photoshop, digital video, and rocket-science houndsrely on specialized 64-bit programs to get their work done faster. And 64-bit programs require 64-bit computers and operating systems to match.

OK, suppose that you do, in fact, have a computer with a 64-bit processor, like an Intel Core 2 Duo or AMD Athlon 64 FX. Even then, you might not want to run the 64-bit version of Vista.

First of all, the 32-bit version runs just great on 64-bit computers; there's no performance penalty.

Second, 64-bit is uncharted territory for most people. 64-bit processors and operating systems have long been used for database servers and other machines that must move large amounts of data quickly. But 64-bit Windows hasn't had much experience running day-to-day productivity programs or video games. If you decide to use 64-bit Vista as your desktop operating system, you're becoming a volunteer tester to give the whole 64-bit Windows notion a shake-down.

Plenty of people say they've gone 64-bit for months with no problems, but an equal number say they have trouble finding stable device drivers for 64-bit Windows. That kind of split is usually a sign that your mileage may vary.

So if you're curious and brave, give the 64-bit version a try. But be prepared to spend some time in the Microsoft Communities Web sites finding answers to issues that come upand paving the way for the rest of the world to run 64-bit Vista without incident.