What is EFI (or UEFI) firmware?

EFI (Extensible Firmware Interface) is a specification for a new generation of system firmware. An implementation of EFI, stored in ROM or Flash RAM, provides the first instructions used by the CPU to initialize hardware and pass control to an operating system or boot loader. It is intended as an extensible successor to the PC BIOS, which has been extended and enhanced in a relatively unstructured way since its introduction. The EFI specification is portable, and implementations may be capable of running on platforms other than PCs.

Originally called Extensible Firmware Interface (EFI), the more recent specification is known as Unified Extensible Firmware Interface (UEFI), and the two names are used interchangeably.  (I tend to use the name "EFI" for anything that was produced or defined before the name change, and "UEFI" for anything since the name change.)

How do I start using EFI firmware?

You must make this choice before installing the OS.

On VMware Workstation, go into VM > Settings > Options > Advanced, and check Boot with EFI instead of BIOS.

Thanks for picture VMware.com

On VMware Fusion, EFI firmware is automatically selected for Mac OS guests.  You do not need to do anything.

On ESXi using the vSphere Web Client, go into Edit Settings > VM Options > Boot Options, and choose under the Firmware section.

On ESXi using the vSphere Client, go into Edit Settings > Options > Boot Options, and choose under the Firmware section.

On any of our products with EFI support, you can also manually edit the virtual machine's configuration file to add the line

   firmware = "efi"

to configure a virtual machine for EFI.  The above user-interfaces do exactly that for you.  You can use this method if you want to play around with EFI in configurations that we don't officially support (such as Linux on EFI in Fusion 7), but of course things might very well break.