Volatile is cv qualifier. Even though Dan Saks has already described in few articles volatile keyword as a promise, still there's more to find out !
Here's more to this topic:
Introduction to the Volatile Keyword [eetimes.com]
Basics explained as a usage by Nogel Jones.
What does volatile mean [blog.regehr.org]
I suggest reading this one which explains volatile with code examples.
Volatiles Are Miscompiled [http://www.cs.utah.edu/~regehr]
Secret life of volatile [codingrelic.geekhold.com]