A VM BIOS (virtual machine basic input/output system) is the set of instructions that controls the booting process of a virtual machine.
As an emulation of a physical computer, most virtual machines require a BIOS to control booting and input/output operations. While a VM BIOS is similar to a BIOS on a physical computer or server, its functionality is often more limited compared to the BIOS of a physical machine. In fact, in most cases the only available setting accessible from a VM BIOS is the boot order. This could be useful if, for example, an administrator wanted to boot a VM image from a DVD, USB drive or other media.
Each hypervisor has a different process for accessing and editing VM BIOS. In Microsoft Hyper-V, administrators can access VM BIOS settings with the Hyper-V Manager. VMware VM BIOS settings can be adjusted through vSphere. Different VM versions or formats also have different VM BIOS settings. For example, in addition to adjusting boot order, BIOS settings for a Hyper-V Generation 2 VM offer a secure boot option, which is a feature that prevents unauthorized code from running on boot up.
Many of the BIOS settings traditionally available on physical machines are passed from the host machine to the VMs. For example, VMs inherit date and time settings from their physical host via virtualization utilities, such as Hyper-V Integration Services and VMware Tools.