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Laptop design has always been about compromise.

Though they've come a long way in the past few years, laptops have never been able to offer the features available in desktop computers, and certainly not at comparable prices. In order to squeeze an entire computer into a portable shell (and have it be power-efficient enough to run on a battery for hours at a timef), computer-makers have to throw features overboard. And the smaller and lighter the laptop, the more compromise there needs to be.

The MacBook Air , Apple's latest Intel-based laptop, is the lightest, thinnest laptop Apple has ever constructed, and according to Apple, it's the thinnest laptop ever made. And in many ways, the story of this laptop is the story of a series of compromises, all made in order to fit an entire Mac in a three-pound package that's three-quarters of an inch thick at its thickest point.

A Silver MacBook

The look of the MacBook Air is an interesting hybrid of Apple's other two laptops. It's got the shiny aluminum shell of the MacBook Pro , along with a backlit keyboard the likes of which has never been seen before in a small Apple laptop. (However, the MacBook Air is far more attractive than the MacBook Pro, thanks to the curved edges that make it look like the offspring of a MacBook Pro and an iPod nano.)

In all other ways, though, the Air is closest to the MacBook: in two of its three dimensions, it's almost identical to the MacBook, differing only in thickness. (And it's a big difference--the MacBook is 1.08 inches thick, while the Air is 0.76 inches thick at its hinge, tapering to 0.16 inches at its front edge.)

The MacBook Air's keyboard, backlighting excepted, is the same square-keycapped design featured on the MacBook. And its 13.3-inch, 1,280-by-800 pixel display is identical in size to the one found on the MacBook.

However, the Air's screen is notably different because of what's lighting it from behind: a light-emitting diode (LED). The LED backlighting is extremely bright, but what's more impressive is that it immediately snaps on to its full brightness. The MacBook, in contrast, starts out somewhat dim and gradually increases in brightness.

Like the MacBook Pro, the MacBook Air takes advantage of a tiny light sensor, located behind a set of microperforations just to the left of its iSight camera, to automatically adjust the brightness of the display and to control the keyboard's backlighting. (If you turn off the lights, the screen dims rapidly and the keyboard lights up. Those who prefer to manually control their screen's brightness can turn off this feature in the Displays preference pane.)

Despite its diminutive size, the MacBook Air doesn't feel fragile. I wouldn't recommend trying to break it over your knee; the keyboard feels solid, as does the Air's entire bottom half. I noticed a bit of flexion on the top of the laptop--the portion behind its screen--but even there the MacBook Air felt sturdy. There's no way to tell how this laptop will fare in high-stress situations, but it certainly feels durable.