The most obvious change is to the iMac screen. Both the 21.5- and 27-inch screens are made with high definition video in mind. Like on many HDTVs, the black border around the new iMac's screen reaches out to the very edge; the aluminum border that surrounded the screen in the previous iMac is gone. This gives the effect of the screen being bigger than it really is. To the chagrin of many, there is no matte screen option. Glossy is your only choice.

While the 21.5-inch iMac isn't much bigger than the previous 20-inch iMac on paper, sitting side-by-side, the 21.5-inch iMac seems . The 27-inch iMac is gloriously big, but one editor said it might even be too big as a desktop Mac.

The iMac now uses an all-aluminum case, whereas the previous iMac has a black plastic back. If you look very closely, you can see a seam between the lower aluminum front panel and the side of the case. The power button is flush with the back panel and is also aluminum, so it feels like the rest of the back. If you're reaching around the back from the front of the iMac, it's not as easy to find as the power button on the old iMac, which had a concave button that had a different texture than the back panel.

Apple says that the iMac screens are LED-backlit widescreen TFT active-matrix LCDs with in-plane switching technology, and can display millions of colors at all resolutions. In the past, Apple has used 6-bit displays on its 20-inch iMacs and 8-bit displays on its larger-sized iMacs. Apple doesn't specify the bit depth on its ; I'm waiting to hear back from Apple about this.

In-plane switching is supposed to help flat-panel displays maintain image quality at any angle, and this seems to help with the new iMacs. I didn't notice any color shifting or loss of image quality when viewing at extreme angles. On the previous iMacs, there was a noticeable color shift-on the old 20-inch iMac, it didn't take much of an angle to see the color shifting.