Biographical Sketch: Dan Greiner is a Senior Scientist and Master Inventor with IBM's Systems and Technology Group where he has worked for the past ten years developing architecture for System Z. He is currently the editor of the z/Architecture Principles of Operation. Prior to IBM, Dan worked for 22 years at Amdahl Corporation in a variety of customer support, marketing, firmware engineering, and management positions. He has been involved with mainframe computers for over 40 years.