Gigabyte's Hybrid EFI

by Rod Smith, rodsmith@rodsbooks.com


Introduction

If you've read my other Web pages, you may be aware that I've taken an interest in the new Extensible Firmware Interface (EFI) and Unified EFI (UEFI) firmware, which supplements or replaces the older Basic Input/Output System (BIOS) firmware. I've used EFI or UEFI in a couple of computers, in VirtualBox, and as add-on products such as UEFI DUET, which enables you to run UEFI atop a standard BIOS-based computer. When my main computer's motherboard died suddenly, though, I ran across conflicting and confusing information about a particular product when I did my hasty research to find a replacement. Specifically, Gigabyte offers several motherboards with what it calls Hybrid EFI to enable support for hard disks over 2TiB in size. Since one of the motherboards I was considering for my necessarily rapid replacement was the Gigabyte GA-78LMT-S2P (rev. 4.0), which uses a Hybrid EFI, I wanted to know more, and ultimately decided to give it a try myself. Although Web forums in particular were filled with confusing information, a few news sites had more reliable information. (See the References section for links.)

Briefly, Hybrid EFI is a UEFI based on the open source TianoCore reference implementation. This implementation is also at the heart of UEFI DUET, which enables you to boot using EFI methods on BIOS-based computers. In fact, conceptually, Hybrid EFI is similar to using UEFI DUET, except that the EFI code is built into the firmware: Underneath the UEFI layer, Hybrid EFI uses an old-style BIOS—specifically, an Award BIOS version 6.00PG, at least in the case of the GA-78LMT-S2P I bought. Once an OS (or even a boot loader) has booted, the underlying BIOS becomes fairly unimportant. Contrary to the implication of many forum posts I found, Hybrid EFI is much more than just a way to get Windows to boot from a disk that's over 2TiB in size. To boot on such a disk, Windows needs to have a full EFI implementation, and Hybrid EFI delivers that. It also enables booting Linux or other OSes in EFI mode. You can install Linux, Windows, or other EFI-enabled x86-64 OSes in EFI mode even on disks smaller than 2TiB, if you so desire. I suspect that you can install in BIOS mode even on larger disks if your OS supports this, but I haven't tested this supposition.

Unfortunately, Gigabyte's implementation leaves much to be desired. Although OSes can see the firmware as a UEFI, and have access to the usual EFI features, the way it's bolted onto the older BIOS provides the user with few options. The most hyped and user-visible EFI feature, a GUI for setting firmware options, is lacking from Hybrid EFI. (A GUI isn't part of the EFI specification, and GUI BIOSes have been produced in the past, so the GUI is really a side-show in terms of EFI development. A GUI is a major marketing, but not a technical, feature of UEFI.) Furthermore, Hybrid EFI is a finicky implementation, which tends to flake out when presented with configurations that deviate even slightly from the optimum, as described in more detail shortly.

The Hair-Pulling Begins
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