(U)EFI is the next generation of BIOS. When you install ESXi 5.0 on VMware Workstation 8, it just uses a regular BIOS. It is however possible to use EFI instead of BIOS. The vSphere Installation and Setup guide states that you shouldn’t change the boot type from BIOS to EFI on an already installed ESXi host. It does work however in VMware Workstation. But for production systems, just stick to t