The following is a brief overview (per VMware) of how virtualization of the CPU, memory, disk, and network works: CPU virtualization Each virtual machine appears to run on its own CPU, or set of CPUs, fully isolated from other virtual machines, with its own registers, translation look-aside buffer, and other control structures. Most instructions are directly executed on the physical CPU, allowing compute-intensive workloads to run at near-native speed. Privileged instructions are performed safely by the patented and patent-pending technology in the virtualization layer. Memory virtualization Although a contiguous memory space is visible to each virtual machine, the physical memory allocated may not be contiguous. Instead, noncontiguous physical pages are remapped efficiently and presented to each virtual machine. Some of the physical memory of a virtual machine may in fact be mapped to shared pages or to pages that are unmapped or swapped out. This virtual memory management is performed by ESX Server without the knowledge of the guest operating system and without interfering with its memory management subsystem. Disk virtualization Support of disk devices in ESX Server is an example of the product's hardware independence. Each virtual disk is presented as a SCSI drive connected to a SCSI adapter. This device is the only disk storage controller used by the guest operating system, despite the wide variety of SCSI, RAID and Fibre Channel adapters that might actually be used in the system. This abstraction makes virtual machines at once more robust and transportable. There is no need to worry about the variety of potentially destabilizing drivers that may need to be installed on guest operating systems, and the file that encapsulates a virtual disk is identical no matter what underlying controller or disk drive is used. VMware ESX Server can be used effectively with storage area networks (SANs). ESX Server supports QLogic and Emulex host bus adapters, which allow an ESX Server computer to be connected to a SAN and to see the disk arrays on the SAN. Network virtualization You may define up to four virtual network cards within each virtual machine. Every virtual network card has its own MAC address and may have its own IP address (or multiple addresses) as well. Virtual network interfaces from multiple virtual machines may be connected to a virtual switch. Each virtual switch may be configured as a purely virtual network with no connection to a physical LAN, or it may be bridged to a physical LAN via one or more of the physical NICs on the host machine. | 