The scanner also tells me that the amount of memory needed is 397.40MB. I guess 1280MB RAM is good for more than three full pages (3.22 pages), while with 256MB RAM only more than a half of page ...

The Max RAM Upgrade Kit from iFixit includes a pair of 16GB DDR4 2400MHz RAM SO-DIMM modules that are compatible with the new iMac desktops, bringing the memory up to 32GB.