When is it required to use 64Bit CPU’s to run vCenter Server?

A.
Never – vCenter wont run on a 64Bit CPU

B.
When you have 200 or less hosts

C.
When you have 200-300 hosts

D.
All the time

Explanation:
ESX and vCenter Server Installation Guide, ESX 4.0, vCenter Server 4.0, page 17. Table 2-5 summarizes the requirements for an extra-large deployment. vCenter Server must be hosted on a 64-bit Windows operating system for this configuration.
Table 2-5. Up to 300 Hosts and 3000 Powered-On Virtual Machines

Product CPU Memory Disk
vCenter Server 4 8GB 3GB
vSphere Client 1 500MB 1GB