Direct Execution Mode vs. Virtualization Mode

ESX has 2 execution modes: Direct Execution Mode & Virtualization Mode. Direct Execution Mode is much more efficient because it has direct access to the host hardware, thus it is the most preferred method of instruction execution. Virtualization Mode is used when Direct Execution Mode is not possible, primarily when an instruction needs access to CPU Ring 0. The VMkernel handles each of these requests, thus it's slower.
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