Everything you need to know about Retina display, Apple's super high-density screen with pixels so small you can barely see them
Retina display is a marketing term used by Apple to indicate a screen density of around 300ppi. At that size, pixels are so small they tend to disappear, making text look sharper and graphics crisp and clean. The first Retina display device was the iPhone 4, which had a 960x640 screen at 3.5-inches, making it 326ppi. The iPod touch followed shortly thereafter. The next was the iPad 3, which had a 2048x1536 screen at 9.7-inches, making it 264ppi. (Because larger screens are generally held further away, a lower density was passable). The Mac went Retina with the 2012 MacBook Pro, and the iPad mini with the Retina iPad mini in 2013.
iMacs, Thunderbolt Displays, and MacBook Airs remain on the Retina want list.