Quoting from InfoWorld
As server hardware continues to go through its refresh process, more and more people are going to start migrating their servers over to the more powerful x64 platforms. The need to migrate to a 64-bit platform will become further accelerated as software manufacturers begin releasing 64-bit only versions of their applications. So the question becomes, can server virtualization help me with this transition from a 32-bit to a 64-bit environment? The answer, unfortunately, is not cut and dry.
64-bit computing seems like the logical next step for server virtualization because of virtualization's resource hog-like nature, consuming as much processing power and memory as the virtual machines were configured to use. And since an x64 architecture typically offers a much higher CPU performance rating as well as an increased memory capacity, it seems like a marriage made in heaven.
But (there's always a but), this is where the "not so cut and dry" part comes into play. You would think that you should be able to go out and purchase an x64 system, install the operating system and virtualization platform, and then begin creating 64-bit virtual machines. Not so.
The first problem lies with the host operating system. Make sure that the host operating system you select is compatible with the x64 platform that you plan on purchasing. VMware ESX Server uses its own custom kernel as the host operating system, and therefore installs on bare metal. VMware offers a hardware compatibility guide to make sure that your hardware is compliant and supported with ESX Server. When installing VMware Server or Microsoft Virtual Server 2005, you must first install a base operating system such as Microsoft Windows Server 2003 x64 Edition. It is important to make sure that your x64 architecture is supported by the Windows operating system. It becomes important to do a little research here and not just assume.
Once you get beyond the host operating system problems, you must then contend with the limitations that surround virtualization and their guest operating systems. While most of the virtualization platforms offer some type of support for 64-bit computing, it is certainly a mixed bag.
The current market leader, VMware, offers some type of support for 64-bit computing on all of its platforms. However, if you want to run a 64-bit guest operating system, it does have limitations on supported processors.
AMD
Opteron, revision E or later
Athlon 64, revision D or later
Turion 64, revision E or later
Sempron 64, revision D or later
Intel
Intel EM64T VT-capable processors
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