How to simulate a retina display (HiDPI mode) in Mac OS X 10.8 Mountain Lion on a non-retina display?

Question

How can you simulate a retina display (HiDPI mode) in Mac OS X 10.8 Mountain Lion on a non-retina display?

Answer 1

If your monitor supports it, it may also be worth setting the DisplayPort version to 1.1 instead of 1.2.

I have a late 2010 Mac Air with a Samsung S27D850 display and had all sorts of intermittent resolution switching issues until I made that change.