Apple's line of newly updated 5K Retina 27-inch iMacs with Skylake will support up to 64GB of RAM, an upgrade from the previous-generation 27-inch Retina iMacs that would only support a maximum of 32GB of RAM



From MacRumors:

According to OWC, The current 27-inch Retina iMac includes four memory slots that support up to 16GB of memory per slot for a total of 64GB. Image via OWC Build-to-order options for the 27-inch Retina iMacs only allow it to be purchased from Apple with a maximum of 32GB RAM, but OWC will offer 16GB modules in 48GB and 64GB configurations for the new iMac. OWC plans to start selling its new 48 and 64GB kits tomorrow, but pricing is not yet available.

  New 27-Inch iMac Supports Up to 64GB of RAM, OWC Offering Upgrade Kits