In any case, Snow Leopard truly is an optimized version of Leopard. It starts up faster (72 seconds on a MacBook Air, versus 100 seconds in Leopard). It opens programs faster (Web browser, 3 seconds; calendar, 5 seconds; iTunes, 7 seconds), and the second time you open the same program, the time is halved.

“Optimized” doesn’t just mean faster; it also means smaller. Incredibly, Snow Leopard is only half the size of its predecessor; following the speedy installation (15 minutes), you wind up with 7 gigabytes more free space on your hard drive. That, ladies and gents, is a first.

Unfortunately, Snow Leopard runs only on Macs with Intel chips  that is, Macs sold since 2006. If you have an older Mac, you’re stuck with Leopard forever.

(Techie note: Popular conception has it that the space savings comes from removing all the code required by those earlier chips. But that’s not true, according to Apple. Yes, that code is gone, but new 64-bit code, described below, easily replaces it. No, Apple says that the savings comes from “tightening up the screws,” compressing chunks of the system software and eliminating a huge stash of printer drivers. Now the system downloads printer drivers as needed, on demand.)

As it turns out, Apple programmers could not leave well enough alone. They disobeyed the original “no new features” mantra. As they pored through all the bits of Mac OS X, they kept stopping and fixing little things that had always bugged them, or coming up with neat little ways to make things better. So:

The Mac now adjusts its own clock when you travel, just like a cellphone. The menu bar can now show the date, not just the day of the week. The menu of nearby wireless hot spots now shows the signal strength for each. When you’re running Windows on your Mac, you can now open the files on the Macintosh “side” without having to restart. Icons can now be 512 pixels (several inches) square, turning any desktop window into a light table for photos.