Analyzing the iMac 5K Retina display: How do you get 5K @ 60Hz from a last-gen GPU? (updated)

Last week, Apple announced a new 27-inch iMac that packs an impressive 5K Retina display. Aswe’ve already detailed, these new 5K displays are thinner, cheaper, draw less power thanks to a more-efficient LED backlight, and, perhaps most importantly, Apple is selling the whole 27-inch iMac system at a mind-blowing price of $2500. That’s the same price tag on Dell’s 5K monitor.

Updated November 4: Sadly, it’s time for a mea culpa. On October 24 we mistakenly identified the iMac with 5K Retina display as having a 30Hz panel. The 27-inch iMac does indeed output 5K @ 60Hz — and to hit those kinds of frequencies, Apple used its own customized timing controller, rather than DisplayPort 1.2 (which can’t drive 5K @ 60Hz). More on that can be found further down the story.