Apple went pixel-happy with its largest iMac on Thursday, announcing Retina Display upgrade to the 27-inch all-in-one computer.

Apple is calling the new screen a "Retina 5K Display," and says it's the world's highest resolution computer display at 5120-by-2880 pixels. (By comparison, 4K displays pack a 4096-by-2160 resolution.) Compared to existing iMacs, the new model has four times as many pixels, but uses 30 percent less energy and EnergyStar 6.1 compliant.

Aside from the higher resolution screen, Apple is boosting the iMac's tech specs. At the baseline, there's a 3.5 Ghz quad-core Intel Core i5 processor, an AMD R9 290x Radeon graphics card, 8 GB of RAM and a 1 TB Fusion Drive. Users can also opt for a 4.0 Ghz Intel Core i7 chip and AMD R9 295x Radeon graphics.

The new machine does command a higher price of $2,499, compared to $1,799 for the non-Retina 27-inch iMac, which is sticking around. The new iMac starts shipping today.