The server defaults to 64-bit MMIO (Memory Mapped I/O). This allows additional PCIe memory address space to be mapped above the standard 32-bit 4 GB of space for PCIe cards that include option ROMs. However, VMware ESXi is incompatible with MMIO space above the standard 4 GB. Therefore, before you install VMware ESXi, you must set the 64 Bit Resources Allocation property to Disabled in the BIOS Setup Utility.
Attempting to install VMware ESXi without disabling the 64 Bit Resources Allocation property might cause the installation to fail or the PCIe cards in the system to function improperly.
To disable this property, see the following procedure: