For more than a decade ago, OS X has been the name for Apples computer systems.
Daily usage patterns are specific to each product and are a mixture of actual and modeled customer use data.
Apple could announce this change in June at its World Wide Developer Conference (WWDC).
Now, over the last two years Apple has been moving towards a more unified naming scheme.
Some of Apples newer products have very clear branding.
Hence, MacOS sounds like a logical advancement of the operating system terminology.
In fact, Apple till the late 90s used to use the name MacOS way back.
It was the name of the operating system since its inception in the 80s.
source: www.techworm.net
