Apple has today announced a new version of its iMac with a stunning 5K Retina display - that's a resolution of 5120 x 2880. That's seven times as many pixels as an HD TV, and 67 percent more pixels than 4K displays. The new iMac is still 5mm despite the new display, plus it uses 30 percent less energy than the previous model. Apple is using a chip to control the display as well as a material called Oxide TF and a low-power backlight. Pricing will start at $2,499.