Ondrej Holzman Twenty-seven-inch iMac with 5K Retina display it's been here for almost a year. In October, according to the latest information, a display with a higher resolution should also arrive in the smaller, 21,5-inch iMac.
Mark Gurman of 9to5Mac citing sources inside Apple reports, that the upgraded iMac will arrive at the end of October together with the new operating system OS X El Capitan. The 21,5-inch iMac, currently offered with a resolution of 1920x1080, will get a resolution of 4096x2304.
The appearance of the smaller iMac should not change, but we can expect new processors (however, the question is whether already the new Skylake series) and, according to analyst Ming-Chi Kuo, also the use of phosphor materials to significantly improve color saturation.
The new 21,5-inch iMac with a 4K display is due to go on sale in November and will most likely be more expensive than the current models. They cost from 33 to 990 crowns. However, Apple will probably continue to offer iMacs with a lower resolution, similar to the 46-inch version. The difference between a large iMac with and without Retina is currently six thousand crowns.
Logically, I think it is better not to give high resolution to 21″. Simply, if you want 4/5K, then buy a 27″ top model, otherwise HD will be enough..
What's logical about that?
theoretically, it is better even on a higher diagonal, but if smartphones already have 2560x1440p, it would not be bad to have a 4k display on a PC, because the Sony Xperia Z5 already has a 4K 5,5" display with a resolution of 3840x2160p