UEFI Support in Windows 8

While Windows has had support for the UEFI (Unified Extensible Firmware Interface) prior to Windows 8, most consumer computers have continued to boot using BIOS Firmware.

This changes with Windows 8, as UEFI Firmware mode is now a Windows 8 client logo requirement. UEFI is also required to enable several features and inprovements, such as:

GUID Partition Table (GPT) Disk Partitioning - GPT Partitions enable larger partitions, and are supported by UEFI. For more details on GPT and advantages of the same  Click Here

Boot From Larger Drives - GPT and native 4K sector disk support in Windows 8 enables support for greater than 2.2TB Boot drives

Secure Boot - Signature checks on early boot components, protecting pre-boot manager components from tampering.
The three main actions related to Secure Boot are:
1.The firmware verifies all UEFI executables and the OS loader to be sure they are trusted.
2. Windows Boot Components verify the signature on each component to be loaded. Any non-trusted components will not be loaded and will   trigger remediation.
3. The signatures on all Boot Critical Drivers are checked as part of Secure Boot verification in WinLoad and by the Early Launch Anti-Malware drive.

Measured Boot - Measured Boot is another boot feature in Windows 8 that is also related to Anti-Malware software. Measured Boot gives the Anti-Malware software a detailed,reliable log of components that loaded prior to the ant-malware driver during startup. This log can be used by anti-malware software or an administrator in a business environment to validate whether there may be malware on the computer, or evidence of tampering with boot components.

Early Launch Anti-Malware - This provides the ability for an anti- malware driver to register as a trusted Boot Critical Driver. This makes it the first non- Microsoft, non-Platform specific code that will run on the computer. The anti-malware driver can then verify other drivers in turn before they are initialized.
Secure Boot helps prevent malware from running before the OS. Early Launch AV helps insure trusted anti-malware software is the first third party component run on each startup.

Trusted Boot - A combination of Secure Boot, Measure Boot, and Early Launch Anti-Malware that helps establish that the system is in a trusted state.

Boot on computer with no VGA Support - UEFI removes the need for VGA support, enabling Windows 8 to be installed on computers that do not use this legacy video technology.