Instapaper developer Marco Arment said he had heard from "multiple sources" that "while an iMac update is indeed coming this fall, it will ".

Arment suggests that the size is one reason why the iMac will not have a Retina display.

As screen sizes get larger, the graphics card requirements also increase. For example, the 27in iMac currently has a resolution of 2,560 x 1,440 - the Retina display resolution on that model would need to be 5,120 x 2,880, although it has been suggested that to qualify for the 'Retina display' definition the resolution would only need to be 3,840 x 2,400 if Apple used 'pixel doubling'.

MacRumours suggests that an update to the iMac should happen soon if Apple is not in fact awaiting Retina displays, since the Ivy Bridge processors, improved graphics chips and USB 3.0 are available now. That report suggests that an iMac launch could happen in tandem with the launch of OS X Mountain Lion at the end of July.