We haven’t even seen the first retina display iPad yet, but just as Apple’s been baking double-sized assets for an iPad HD into iOS since iOS 4, OS X Lion lays down some groundwork for the first Retina Display iMacs and MacBooks.
The support comes by way of code to push pixels in “HiDPI” mode, or “High Dots Per Inch” mode. It’s not on default, but if you’ve downloaded Xcode for Lion, you can enable it in the Quartz Debug Application found in the Developer Directory.
There’s not a lot to see so far: in fact, all it will do is allow you to access resolutions that are half the maximum resolution your monitor is capable of. But that’s exactly what’s interesting about HiDPI mode, because according to MacRumors, it proves that Apple will take an identical approach to making Macs ready for Retina Displays as they have with the iPhone: namely, Apple will multiply the resolution of existing iMac and MacBook displays by two (quadrupling the number of pixels) so as to make sure that OS X’s UI elements scale up nicely.
While this is interesting (and pretty much proves that the iPad HD will have a 2048 x 1656 Retina Display, and not any more esoteric resolution), Retina Display Macs are likely at least a few years off. New display technology starts off as only being affordable in smaller screen sizes, creeping out to larger displays over time. That’s why the iPhone and iPod Touch lines were the first to get Retina Displays. If Apple hasn’t even managed to deliver a 9.7-inch Retina Display suitable for the iPad yet, we’ve got a few years to wait before we get a 27-inch Retina Display attached to our iMacs.