I have assumed that you know what virtualization is and now want to explore Oracle's version of virtualization. Still we feel that a quick introduction and a brief history of virtualization can never hurt. It is very hard to compact the past 50 years of IT achievements about virtualization, but I will attempt to cover it (very) briefly.
To take a look at x86 virtualization—a concept that often confuses a lot of IT Managers (even today) when they are confronted by consultants, vendors, or even internal staff, we have to go back to the 60's when IBM first introduced "Time sharing". Time sharing is basically sharing resources of expensive machines among several users, something we also call multi-tasking. Back then the machines were so expensive that it was necessary to come up with something creative. Fast forwarding 50 years we have come a full circle with the re-introduction of virtualization—only this time it has come to dominate the x86 servers. This was done, or should we say initiated, by VMware, which went on to create this huge ecosystem around it. Then came Xen, an Open Source project that began its subtle penetration into the ASP space and hosting providers, and which was later to be acquired by Citrix. Microsoft, not to be left behind in the process, carried on to acquire Connectrix, and after conducting several rebranding exercises on its hypervisor, later introduced Hyper-V.
Oracle worked on Xen's Open Source technology and introduced its Xen-flavored virtualization software as well. The list is quite exhaustive as the virtualization market has become rather huge. You might even say that in the drive to battle the oversubscription monster, the mushroom effect of all of the start-ups has created the over-subscription dilemma for themselves.
The introduction of virtualization is definitely the most significant event in the history of IT. It can drive down the costs dramatically and provides several open and public platforms to general public in the form of "public clouds". VMware, Microsoft, and several other firms are constantly fighting for the "private cloud" space where the mother-of-all virtualization, IBM, is also fighting. There has been a huge data center build-up across the world where all IT firms are battling to spread their wings and go after the Cloud Computing space.