According to OWC (via MacRumors), it seems that they have discovered that the new iMacs include four memory slots, with each slot supporting up to 16GB of RAM. This means that technically the iMacs could be stuffed with 4 x 16GB of RAM, resulting in a whopping 64GB of RAM in total.
At the moment the configuration options for the 27-inch iMacs only allow for a maximum of 32GB of RAM, which by itself does seem like overkill for most users, but if for whatever reason your work demands that you have as much RAM as humanly possible, then you will be pleased to learn that the computer will support it.
That being said, OWC will also be selling RAM kits for the iMac. They do not come cheap though and are priced at $1,195 for the 64GB kit. However if you don’t need that much RAM, OWC is also selling 16GB standalone modules at $329.99 each, 32GB kits with 2 x 16GB modules priced at $599, and 48GB kits with 2 x 16GB + 8GB x 2 at $729.