2002 the year Live Migration was born

In 2002, a group of professors from three universities designed and implemented the NomadBIOS paravirtualized hypervisor, and were the first to show how a VM running a production-class operating system could be migrated between two hosts with almost imperceptible downtime, less than 100 ms. Such functionality, now commonly referred to as "Live Migration", has since become a hallmark of VM systems, and is supported in products from VMware, Citrix, Oracle, and planned in a future product announced by Microsoft. When you are interested in the background of this VMotion technique, you should really take a look at this PDF.