理解全虚拟化，半虚拟化和硬件辅助

In 1998, VMware figured out how to virtualize the x86 platform, once thought to be impossible, and created the market for x86 virtualization. The solution was a combination of binary translation and direct execution on the processor that allowed multiple guest OSes to run in full isolation on the same computer with readily affordable virtualization overhead. The savings that tens of thousands of companies have generated from the deployment of this technology is further driving the rapid adoption of virtualized computing from the desktop to the data center. As new vendors enter the space and attempt to differentiate their products, many are creating confusion with their marketing claims and terminology. For example, while hardware assist is a valuable technique that will mature and expand the envelope of workloads that can be virtualized, paravirtualization is not an entirely new technology that offers an “order of magnitude” greater performance. While this is a complex and rapidly evolving space, the technologies employed can be readily explained to help companies understand their options and choose a path forward. This white paper attempts to clarify the various techniques used to virtualize x86 hardware, the strengths and weaknesses of each, and VMware’s community approach to develop and employ the most effective of the emerging virtualization techniques. Figure 1 provides a summary timeline of x86 virtualization technologies from VMware’s binary translation to the recent application of kernel paravirtualization and hardware-assisted virtualization.