Apple's OS X operating system is based upon the widely-used Unix operating system. It is a multitasking, multiuser computer operating system that originates from AT&T Unix and developed in the 1970s at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and others. My first acquaintance with Unix dates from the mid-70s, about a decade before the development of OS X. This edition addresses all versions of OS X up to and including Mountain Lion. I am not aware of later editions of this book covering Mavericks or Yosemite operating systems. O'Reilly is another excellent publisher of computer text books. The author, David Taylor, is well known for his books on the OS X operating system.