Datasheet

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CHAPTER 1 VMware VSphere 4 OVerView
Recently, AMD and Intel have introduced newer processors that also support memory manage-
ment virtualization. You’ll learn more about this in the next section. Virtualization using these
second-generation hardware-assisted processors usually performs better than binary translation.
Consequently, with the release of vSphere, VMware ESX, and ESXi now default to hardware-
assisted virtualization out of the box, but you do have the choice to override this setting.
VMware vSphere also supports paravirtualized Linux guest operating systems—Linux kernels
that include Virtual Machine Interface (VMI) support—that are virtualization-aware. Because
the VMI standard is supported out of the box in newer Linux kernels, there is no need to main-
tain separate distributions of Linux specifically for virtualization.
Hardware-Assisted Memory Virtualization
Memory management in virtual machines is challenging compared to physical machines, espe-
cially when it comes to virtual memory address translation. In a physical machine, the operating
system uses page tables to translate memory addresses from an application’s “virtual” space into
the machine’s physical memory addresses. Similarly, in a virtual machine, guest virtual memory
addresses are translated to guest physical addresses using the guest OS’s page tables. However,
the guest OS does not have access to the physical machine memory; ESX controls the access to
the actual physical memory. ESX performs the final translation to machine physical memory
addresses by implementing a set of shadow page tables for each virtual machine. Creating/
maintaining the shadow page tables adds both CPU and memory overhead. This overhead can
be significant for virtual machines running several processes or using multiple virtual CPUs.
Both AMD and Intel have introduced hardware-assisted memory management capabilities to
alleviate this situation. Processors supporting hardware-assisted memory management implement
an additional level of page tables in hardware. These hardware page tables keep track of guest
Figure 1.2
VMware vSphere
virtualization
technology options
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