Hardware Requirements For 64-Bit Guest Operating Systems

 VMware's virtual machine monitor has traditionally used segmentation to provide isolation between the guest operating system and the virtual machine monitor. This is necessary because the guest operating system and virtual machine monitor share the linear address space.

AMD
Segmentation support is missing from the initial AMD64 processors (that is, revision C and earlier) while running in long mode. As a result, AMD64 processors prior to revision D do not have an efficient mechanism for isolating the virtual machine monitor from 64-bit guest operating systems.

A limited form of segmentation was reintroduced in long mode, in revision D AMD64 processors. As a result, AMD64 processors must be revision D or later to run 64-bit guest operating systems.

Note: Because AMD Opteron and Turion processors do not ship in revision D, AMD Opteron and Turion 64 processors must be revision E or later to run 64-bit guest operating systems.

Intel
Intel EM64T CPUs do not have segmentation support in long mode. If the Intel EM64T CPU is VT-capable, it comes with hardware virtualization support (Intel's Vanderpool Technology). This hardware virtualization support allows Workstation and VMware Server to work around the lack of segmentation, making it possible to run 64-bit guest operating systems on Intel EM64T VT-capable CPUs.

32-Bit CPUs
Please note that Workstation and VMware Server require a 64-bit CPU to run a 64-bit guest operating system. While it is theoretically possible to emulate a 64-bit instruction set on 32-bit hardware, doing so most likely results in unacceptable performance degradation.

VMware distributes a free utility that can be used to determine whether or not your CPU is suitable for running 64-bit guest operating systems. You can download this utility from the VMware Web site at www.vmware.com/download/ws/#utilities. VMware Server includes this utility in its product distribution, so you don't need to download an additional tool.

Workstation 5.5 and VMware Server 1.0 support virtual machines with 64-bit guest operating systems only on host machines that have one of the supported 64-bit processors:

• AMD Athlon 64, revision D or later
• AMD Opteron, revision E or later
• AMD Turion 64, revision E or later
• AMD Sempron, 64-bit-capable revision D or later (experimental support)
• Intel EM64T VT-capable processors (experimental support)


Need a short answer for the question "Why Intel-VT/AMD-V for 64 Bit guests"? Here we go.

Running 64-bit binary translation requires "segment truncation" support. Modern OSes don't even use segments anymore, so both AMD and Intel removed segments from their x86-64 specs. Turns out VMware's binary translation technology does use segments ... AMD added limited (but good enough) support early on (RevC Opterons did not have it, RevD and later do) specifically for VMware; Intel does not support the segment truncation feature, so on Intel VT is necessary instead.

Either VT/SVM or segment truncation can be used to protect the VMM from being overwritten by the Guest OS, but at least one of these technologies is required. (We have internal builds that run without protection, but they are used for benchmarks only and are unsafe for real-world use).