Thanks to www.engadget.com at WWDC
10:36AM "Second one, this is a biggie. Something we call the Retina Display. What’s that? In any display there are pixels. We dramtically increased the pixel density, Four times the amount."
10:37AM "Why is that important? Let’s say we want to draw the letter A — as you can see, we can get far more precision. And we play all sorts of tricks." He’s showing anti aliasing.
10:37AM "Because we have four times as many pixels, we get really, really sharp text. Now the retina display as 326 pixels per inch." Wow.