Depending on the guest operating system, when you use a custom configuration, the New Virtual Machine wizard prompts you to select the firmware type the virtual machine uses when it boots.

This option appears in the New Virtual Machine Wizard when the guest operating system is supported with the UEFI firmware type. Otherwise, the BIOS firmware type is selected by default.

Table 1. Firmware Type Options
Option Description
BIOS The virtual machine firmware uses BIOS when booting.
UEFI The virtual machine uses UEFI when booting.

If you select UEFI, depending on the guest operating system, you might have the option of enabling UEFI Secure Boot.

See Configure a Firmware Type.