Added Time, Clocks, and the Ordering of Events in a Distributed System 

Time, Clocks, and the Ordering of Events in a Distributed System 

Leslie Lamport 
Massachusetts Computer Associates, Inc. 

Linked from: http://research.microsoft.com/en-us/um/people/lamport/pubs/time-clocks.pdf

Communications the ACM 
July 1978 
of Volume 21 
Number 7