Apple has just announced a brand-new Retina 27-inch iMac. Apple is spreading Retina displays across the lineup, with the iMac leading that charge. This is the highest resolution screen in the world, according to Apple, with 14.7 million pixels. This is a 5K display — more than seven times the pixels of a HDTV. The screen builds on the technology Apple built on the iPhone and iPad, but to a whole new scale.