The last significant update Apple iMac line of candy bars happened at the end of 2009. However, the new «unibody-aimags" is not very different from previous members of the series, available back to 2007. Much more important change was the transition to a new type of screen: 21.5 "and 27.0" instead of 20.0 "and 24.0". Also installed were extremely LCD matrix IPS-type LED-backlit.
As such, the iMac has experienced the change of generations of processors with Core 2 Duo up to today's Core i5/i7, based on the architecture Sandy Bridge. However, if we look closely, you will notice some additional changes in the latest Apple iMac. Perhaps the most obvious - is to add support for interfaces Thunderbolt. However, there are others, too, is very important. In sum, they accumulate so much that one might think about the next "jump", which Apple does about once every two years.