Quoting from the Egenera official announcement:
Egenera Inc., a leader in utility computing, today announced that it has been granted a patent for server failover technology by the United States Patent and Trademark Office. Egenera has received U.S. patent number 6,971,044 for software that enables high availability of Egenera servers in a virtualized environment. This technology has been a key contributor to the Egenera BladeFrame system’s value proposition since the product was launched in 2001.
Egenera’s failover approach offers customers quantifiable benefits over traditional schemes, which generally require a one-to-one ratio of production to backup machines. By enabling primary-to-failover ratios as high as 23 to one, the Egenera BladeFrame system consolidates servers, lowers datacenter costs, increases utilization and provides unprecedented flexibility in the allocation of processing resources…