iPhone 4's Retina display explained | Phones | iPhone Central | Macworld: To put it simply, Apple’s figurative Retina display is an LCD that boasts a super high pixel density by squeezing a 960-by-640-pixel resolution into 3.5 inches—a pixel density of 326 pixels per inch (ppi).
The Retina display has four times the number of pixels as previous iPhones; its screen size is unchanged, resulting in double the pixel density. When compared to the now $99 iPhone 3GS, which has a 163ppi screen with a 480-by-320 resolution, it’s easy to imagine just how this new screen will shine.
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