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docs/refind/bootmode.html

href="mailto:rodsmith@rodsbooks.com">rodsmith@rodsbooks.com</a></p>

<p>Originally written: 3/14/2012; last Web page update:

11/12/2018, referencing rEFInd 0.11.4</p>

2/12/2020, referencing rEFInd 0.11.5</p>

<p>This Web page is provided free of charge and with no annoying outside ads; however, I did take time to prepare it, and Web hosting does cost money. If you find this Web page useful, please consider making a small donation to help keep this site up and running. Thanks!</p>

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<p>Before you invest time in downloading and trying to install rEFInd, you may want to verify that you can actually use the program at all. rEFInd is useful only on EFI-based computers, not older BIOS-based computers. In fact, most EFI-based <i>x</i>86-64 computers provide a Compatibility Support Module (CSM), which is essentially a BIOS emulation mode. Some EFI implementations are in fact built atop a conventional BIOS, and retain BIOS's boot abilities via this underlying code. Thus, it's possible that you're currently booting a modern EFI-capable computer in BIOS mode.</p>

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<h4 class="tight">Contents</h4>

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<p>Unfortunately, determining which mode you're using can be tricky; the clues are subtle or hidden in ways that require specialized knowledge to extract. This page will help you figure it out. I first present general information on identifying your hardware's capabilities. I then describe ways to identify your current boot mode in both Linux and Windows.</p>

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<h2>Identifying Your Hardware's Capabilities</h2>

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<p>Let's get the easy case out of the way: If you have a Macintosh with an Intel CPU, it's got EFI capabilities, and you'll be able to use rEFInd. Earlier Macs with PowerPC CPUs use OpenFirmware, and rEFInd can't be used with them. If your computer shipped new with Windows 8 or later, it almost certainly supports EFI; Microsoft requires that computers that bear a Windows 8 (or later) logo support EFI, and boot in EFI mode. Most x86 and x86-64 computers released after late 2011 support EFI, although there are some laggards, particularly among server-class machines. Almost everything sold new since about 2014 is based on a decent EFI implementation.</p>

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<p>For everything else, it can be harder to tell. Your best bet is to locate a PDF version of your computer's or motherboard's manual and search it for the string <i>EFI</i>. Checking your firmware's options via the firmware setup utility (typically access by pressing Del, F2, F10, or F12 at boot time) is also worth doing, but you'll need to check every option yourself. Most EFI-enabled PCs include at least one reference to an option you can set; however, manuals and firmware setup tools often don't make a big deal of this feature, particularly on boards with relatively primitive EFI support. For instance, the manual for a Gigabyte GA-78LMT-S2P motherboard includes the following paragraph, on p. 28:</p>

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<p>A casual reader might easily overlook this option, or misinterpret it to mean that the feature is much less important than it is. In fact, this particular motherboard offers very poor control over its EFI vs. BIOS booting features. (See <a href="http://www.rodsbooks.com/gb-hybrid-efi/">my Web page on this EFI implementation</a> for details.)</p>

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<p>A casual reader might easily overlook this option, or misinterpret it to mean that the feature is much less important than it is. In fact, this particular motherboard offers very poor control over its EFI vs. BIOS booting features. (See <a href="https://www.rodsbooks.com/gb-hybrid-efi/">my Web page on this EFI implementation</a> for details.)</p>

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<p>Some manuals omit even mention of EFI, and instead refer to "legacy boot" or some similar term, referring to BIOS-style booting. The firmware for my ASUS P8H77-I motherboard uses the technical term <i>CSM,</i> which of course will be baffling to the uninitiated. (I referred to it earlier. It's the <i>Compatibility Support Module</i>—in other words, the BIOS support code.) Such references may imply that the firmware supports EFI booting if the "legacy boot" mode is disabled or restricted in some way.</p>

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<p>Understated EFI features often indicate a slapdash approach to EFI. Such systems sometimes implement EFI as a layer atop a conventional BIOS. More modern EFIs, though, completely replace the BIOS. Some manufacturers, such as ASUS and its sibling ASRock, are now actively promoting their more advanced EFI implementations. Such products often come with flashy new GUIs in their firmware.</p>

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<p>Positive identification of EFI support in your firmware does <i>not</i> guarantee that your current OSes are booting in EFI mode. (Mac OS X booting on a Mac is an exception to this rule, though.) For that, you'll need to run some tests in your running OSes.</p>

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<p>Positive identification of EFI support in your firmware does <i>not</i> guarantee that your current OSes are booting in EFI mode. (MacOS booting on a Mac is an exception to this rule, though.) For that, you'll need to run some tests in your running OSes.</p>

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<h2>Identifying Your Linux Boot Mode</h2>

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<p>An important caveat with this method is that you must examine your boot disk. It's possible to use GPT on a data disk even on a BIOS-based computer, or to use an MBR data disk even on an EFI-based computer. Thus, if you examine the wrong disk, you can be led to an incorrect conclusion about your computer's boot mode.</p>

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<p>Another caveat relates to the use of a <a href="http://www.rodsbooks.com/gdisk/hybrid.html">hybrid MBR,</a> which is a variant on a GPT disk that's most often used on Macs to permit booting Windows in BIOS mode and OS X in EFI mode. Most Windows tools will identify a hybrid MBR disk as an MBR disk, but most non-Windows tools will identify it as a GPT disk. Of course, as hybrid MBRs are generally used to enable dual-booting Windows and OS X, and as OS X boots in EFI mode, you should be able to install rEFInd from OS X to help manage such a dual-boot configuration.</p>

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<p>Another caveat relates to the use of a <a href="https://www.rodsbooks.com/gdisk/hybrid.html">hybrid MBR,</a> which is a variant on a GPT disk that's most often used on Macs to permit booting Windows in BIOS mode and macOS in EFI mode. Most Windows tools will identify a hybrid MBR disk as an MBR disk, but most non-Windows tools will identify it as a GPT disk. Of course, as hybrid MBRs are generally used to enable dual-booting Windows and macOS, and as macOS boots in EFI mode, you should be able to install rEFInd from macOS to help manage such a dual-boot configuration.</p>

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<p>This document is licensed under the terms of the <a href="FDL-1.3.txt">GNU Free Documentation License (FDL), version 1.3.</a></p>

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<p><a href="using.html">Learn how to use rEFInd</a></p>

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<p><a href="http://www.rodsbooks.com/">Return</a> to my main Web page.</p>

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<p><a href="https://www.rodsbooks.com/">Return</a> to my main Web page.</p>

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