The smaller iMac gets a 4K display, all the 27-inch models have 5K
 

Apple's big fall keynote happened more than a month ago, so it's a bit late for Tim Cook to be saying "one more thing." Sure enough, though, the company just unveiled a refreshed line of iMacs, including a 21.5-inch model with an optional 4K (4,096...

http://www.engadget.com/2015/10/13/4k-imac/