With VI3 you could run on either 32-bit or 64-bit server hardware but vSphere requires 64-bit hardware because the VMkernel and Service Console are now 64-bit. I did a tip a while ago for searchvmware.com that talks about this in detail and shows how you can test your hardware to see if the CPU supports 64-bit and has some of the other CPU features that vSphere needs for certain features. To briefly summarize that tip:
- Long mode is required to be able to install vSphere, it will not install without it.
- To be able to run 64-bit VM’s on vSphere either the AMD-V or Intel-VT feature is required. Without it you can still run vSphere but are limited to using 32-bit VM’s.
- For the Fault Tolerance feature to work you need specific processors that support Lockstep technology, you can read this KB article to find out which ones have this feature.
Here are some links to various information that can help you better understand all this:
- VMware vSphere: Got 64-bit hardware?
- Processors and guest operating systems that support VMware Fault Tolerance (KB Article)
- VMware Fault Tolerance: What it is and how it works
- Lord of the virtual rings: Why hardware matters to your VMs
- An Introduction to 64-bit Computing and x86-64
- Understanding the Microprocessor
- Platforms and Tools for the AMD Athlon 64 Processor
- Hardware and firmware requirements for 64bit guest operating systems (KB Article)
- VMware and CPU Virtualization Technology