(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 the guide and reinstall the host using EFI instead of BIOS on your hardware server.

Now, your normal Virtualized vSphere host in VMware Workstation uses a BIOS.  Notice this in the startup screen when you boot the VM:

Power down your Virtual ESXi host.  Go to the location where the vmx file is stored and edit it with your favorite editor.

Add the line firmware = “efi” somewhere in the vmx file.

Close and save the vmx file.  Power On the ESXi host.  You’ll notice the progress bar at the bottom during the boot is gone:

If you look into the vmware.log you can also see some references that he’s using EFI now:

Et voila, your ESXi hosts are now booting from EFI instead of BIOS!

Tip: if you press ESC during the boot, you can configure some EFI parameters.  Play with it and learn to know if since EFI will replace BIOS gradually!