A Virtual BIOS or UEFI refers to the emulated version of BIOS (Basic Input/Output System) or UEFI (Unified Extensible Firmware Interface) used within a virtual machine (VM). These virtual firmware interfaces serve the same basic purpose within a VM as their physical counterparts do in physical machines: to initialize and test system hardware components, and to load the OS or another bootloader from the boot device.

Here are some key points about virtual BIOS or UEFI:

  1. Emulation: In virtualization, the virtual BIOS or UEFI isn’t a separate chip as in physical hardware. Instead, it’s emulated by the hypervisor, giving the VM an environment that behaves as though it has its own BIOS or UEFI.
  2. Configuration: VMs often allow users to enter and modify settings in the virtual BIOS or UEFI, similar to how you might enter the BIOS or UEFI settings of a physical machine. This can be used to change boot order, enable or disable certain features, or perform other configuration tasks.
  3. Compatibility: Offering a virtual BIOS or UEFI ensures that standard operating systems can be installed on a VM in the same way they would be on physical hardware. This helps maintain compatibility and eases VM provisioning and management.
  4. Transition to UEFI: As with physical systems, there’s been a trend in virtualization platforms to move from traditional BIOS to UEFI due to its enhanced capabilities, such as faster boot times, improved security features (like Secure Boot), and support for larger disk drives (via GPT).
  5. Security Features: Virtual UEFI can support features like Secure Boot, which ensures that the OS loader is signed with a known certificate, adding a layer of security against malware or unauthorized OS modifications.
  6. Vendor Implementations: Virtualization platforms and hypervisors might have slight variations in how they implement and present virtual BIOS or UEFI options. For instance, VMware’s vSphere provides a virtual EFI firmware for VMs, while Microsoft’s Hyper-V also offers a virtual UEFI for its VMs.
  7. Performance: The virtual BIOS or UEFI doesn’t typically impact the performance of the VM once the OS is loaded. However, the boot-up time can vary based on the configuration and the specific firmware interface used.

In summary, the virtual BIOS or UEFI in a VM serves the same foundational role as in a physical machine, ensuring the correct initialization and booting process. As virtual environments aim to emulate real hardware to provide flexibility and portability, the inclusion of virtual BIOS or UEFI is a crucial component in that emulation.