eBook: The Green Data Center - Energy-Efficient Computing in the 21st Century, Chapter 2, 2009 Update
Ordinary rack servers are responsible for the bulk of the IT energy crisis--both in terms of the number of units in place and the amount of energy they waste.
This document explains about servers which present the most important opportunity and energy-efficient power supply which is the most important aspect of improving servers.
These technologies reduce energy usage per server, and virtualization and other usage scenarios can help reduce the number of servers in data centers. Implementing these approaches in concert can yield substantial energy savings and potentially cut server energy consumption in half.