updated 03:49 pm EDT, Tue May 20, 2014
May help to support 4K on MacBook Pro
A subtler change with OS X 10.9.3 is an increase in the available VRAM for newer Macs, reports note. Certain machines -- including the 2013 Retina MacBook Pro, and 2013 and 2014 MacBook Airs -- now have access to 1,536MB of VRAM (1.5GB) instead of 1,024. The difference can be spotted by going to OS X's System Information pane.
Apple hasn't specified a reason for the improvement, and in fact it's completely undocumented. It may however suggest how Apple brought expanded 4K support to the Retina MacBook Pro, which isn't as powerful as the other 4K-capable Mac, the 2013 Mac Pro. That might not explain the improvement on the MacBook Air, unless Apple has identified 2013 models as a baseline.