I've seen this question asked in various places with only partial answers, so I'm aiming to provide something like a complete guide to boot schemes ;)

First of all, some background information you will need:

• BIOS booting usually requires MBR partitioning, although some bootloaders support other partitioning schemes, like GPT.
• UEFI boot usually requires bitness of the OS matches the bitness of the firmware - and the vast majority of UEFI-based machines have 64-bit firmware.

scenarios when you need to use the BIOS

• you are installing an older OS that does not support UEFI booting (such as Windows Vista SP1 or earlier), or
• you need to install an OS with a different bitness than the firmware (i.e. 32-bit OS on a machine with 64-bit UEFI, or vice versa)

note that the OS is nominally require UEFI can often be forced to boot on BIOS-based machines using a specially designed bootloader 1 . For example, this is the case with OS X - as any Hackintosh enthusiast can tell you.

if you plan to dual boot and install a second OS...

while difficult, it is possible to convert between MBR and GPT schemes and reinstall the bootloader for a different mode.

It is also possible to boot one OS via UEFI, the other via BIOS. Sometimes you won't have a choice, like if you already have a 64-bit UEFI-based Windows installation and want to install 32-bit Linux along with it. Or some old and/or exotic OS that doesn't support UEFI. But think twice, are you really necessary to do this.

So the bottom line: just stick to the boot scheme you already have on your machine if you don't have that choice. It is almost always in the right direction.

how do i know which boot scheme my machine is using?

the rule is:

• if it's a Mac, it uses UEFI; some early Intel based models used EFI32, all models since 2008 use standard 64-bit UEFI.
• if it is a branded computer shipped with Windows 8 or later, it uses UEFI; Microsoft requires Secure Boot (which requires UEFI) to be enabled by default on all computers that conform to the Windows logo specification starting with Windows 8.
• if it's a PC shipped with Windows XP or earlier, it uses the BIOS.

with PCs that shipped with Windows Vista or 7, or with Linux, as well as DIY PCs or those sold by small local businesses, you can never be sure just by sight. There are several ways to determine the boot mode in this case:

• you can examine the partition table. If it's a GPT disk and has an "EFI system partition" (usually before the main OS volume), it boots in UEFI mode. Otherwise it is BIOS mode.
• you can enter the BIOS/UEFI setup program and find the boot priority settings. If it displays entries that say EFI or UEFI, and/or they somewhat describe the operating system (such as "Windows Boot Manager" or "Ubuntu"), it boots in UEFI mode. If it only shows the drive model number at best, it's BIOS mode.

if you are installing the first OS on a new machine or intend to clean up the hard drive...

first of all, check if you have a choice. Enter the BIOS/UEFI setup program and look for options like "boot mode" which can be switched between "UEFI", "Legacy", "UEFI+Legacy", something like that. It can also be called something like "Enable UEFI Boot" or "Enable Legacy Boot", or mention the term CSM. if there is no such option in your firmware you are out of luck and should stick with what you have- on older machines that will be in BIOS mode; there are also some newer machines (like the Microsoft Surface line) that only support UEFI mode. If you're still not sure what you have - search for "secure boot" in settings - if it's mentioned anywhere, it's UEFI.

If you have a choice... Consider the benefits of both modes.

advantages of UEFI

• faster boot and better power management. 2 This is especially true for Windows - depending on various factors, fastboot UEFI can even be twice as fast as legacy boot. With Linux, the difference will be less, but still present. This is because a BIOS-booted OS needs to reinitialize some hardware that may have already been initialized, the OS source code needs to be loaded in very slow legacy modes, etc. With Linux, you can also get rid of GRUB completely ( or equivalent) and load the kernel directly from the firmware, which can also speed things up a bit. Also, things like rebooting, sleeping, hibernating, etc. can sometimes partially or completely bypass POST , further improving the overall speed of downloads and force operations.
depending on your use case, this may be more of a hassle than an advantage (but most hardware allows you to turn it off), and its actual security merit is limited - but still, having additional signature verification at the firmware level can provide additional protection against rootkits . Just don't assume that your system is secure just because it uses secure boot, it's too erroneous to make such assumptions.
• improved support for large disks. The MBR partitioning scheme does not support disks larger than 2 TiB. You can still boot from such large drives in the BIOS using hybrid partition tables and an extra bootloader partition (which most OSes create by default anyway), but this is better supported in UEFI. Also, GPT doesn't have that 4-partition MBR limitation, freeing you from nonsense like "extended partitions". There's almost nothing you can't do on top of MBR with patchwork - but it's supported elegantly and natively without the need for patchwork ;)
• native multi-boot. UEFI allows you to initially announce that there is more than one operating system drive on the same hard drive - you can then choose between them from the firmware user interface, without the need for an additional bootloader. While this isn't always the most convenient option for multibooting, it should reduce issues like updating the OS or overwriting the bootloader with antivirus software, etc.
• best software control. some UEFI settings (in particular, boot order) can be changed by the OS in a standard way. This allows you to order things like "shutdown and reboot from CD" (or "boot another OS" in the case above) from the operating system, without having to enter the firmware user interface.

BIOS advantages

• an easier download process. simpler as in simpler by design - not necessarily simpler for modern hardware (which is why it's slower). with UEFI it is always possible to sequentially boot only removable media– bootloader entries for OS on internal disks are stored on the motherboard. That's why on a UEFI-based machine, when replacing a hard drive or moving drives between machines, you'll need a recovery environment on removable media (or an EFI shell in firmware, which is sometimes available on DIY-market motherboards but almost non-existent on branded machines) to restore the internal bootloader configuration for the new drive. In contrast, the BIOS simply loads the first sector of the drive, making it easy to clone and move hard drives between machines (assuming there are no driver issues, of course).
• more flexible OS options. versions of Windows older than Vista SP1 cannot boot via UEFI. Likewise for older Linux distributions. Also, it's generally not possible to boot an OS with a different bitness than firmware - and the vast majority of UEFI-based systems are 64-bit, meaning no 32-bit OSes for legacy boot. On the contrary, almost everything can be loaded through the BIOS. one
• less mistakes. UEFI implementations quite often have subtle but fatal flaws and bugs that can cause the motherboard to brick by deleting the firmware configuration or loading the wrong driver. By contrast, the BIOS has been around since 1981, and at least the way it interacts with the OS hasn't changed much in that time. In modern usage, this is a very thin layer that is only used at boot time, and is also mostly unidirectional, with the OS having almost no access to what's left inside the BIOS. This means that it is much more difficult to fatally break things.

bottom line

my advice would be to boot via legacy bios if you:

• actually setting up VM-UEFI on VM hypervisors tends to be limited and experimental; BIOS boot is much better supported
• need to boot a 32-bit OS on a 64-bit machine
• there is a firmware, as you know, especially buggy
• frequently swap or move hard drives between machines

otherwise, it's better to go with UEFI. It's faster, safer and comes with better functionality.

footnotes

1. you can even install a UEFI environment over BIOS. The TianoCore duo builds to do something on purpose, but such a setup is generally impractical for real setups. If you don't have a BIOS-only machine and you're installing an experimental OS that can't be booted in any other way than via a UEFI bootloader - you don't want to do that.
2. some early UEFI firmware may have a "bolt-on" UEFI bootloader on top of the BIOS-based firmware. In such rare cases, the BIOS may boot faster, but this is not representative of most hardware.

In the BIOS and UEFI of modern motherboards and laptops, you can find a setting called USB Legacy, which is most often located in the "Advanced" sections of the firmware interface. Today we want to talk about why this setting exists and what it is responsible for.

Almost all computers have had built-in ports for the USB bus for many years, which is used to connect most peripheral devices. Most often, these are keyboards, mice and external drives - it is for their correct operation in BIOS that the option in question is intended.

The latest BIOS variants, known as UEFI, support a graphical interface to make it easier to work with the firmware. This interface actively uses the mouse, as opposed to purely keyboard control in the "regular" BIOS. The USB protocol has known restrictions on low-level access, so without activating the USB Legacy parameter, mice that are connected to this connector will not work in UEFI. The same applies to USB keyboards.

The situation is similar with flash drives, but there is one important nuance. Boot drives with Windows 8 and newer usually work without enabling Legacy mode, while media with Windows 7 written or some distributions on the Linux kernel may not be recognized. The fact is that to record the "seven" (or older Microsoft systems) or Linux-based distributions, a partition table is used, which is not supported by modern UEFI out of the box, which is why the USB Legacy parameter must be activated.

Enable USB Legacy

It is not a problem to activate the USB operating mode in BIOS for legacy systems, and further we will describe the procedure for the main firmware options. It goes without saying that the first step is to enter the BIOS interface - for this you will need to restart the computer and press a certain key during the boot process of the machine.

Phoenix Award BIOS

AMI BIOS

Note! The modes are mutually exclusive: UEFI flash drives will not work with Legacy active!

Other BIOS Options
In less common variants of firmware interfaces, you should focus on the possible location of the described option - section "Advanced" or "USB ports".

It is also worth bearing in mind that in some cases USB Legacy support in the BIOS of a desktop computer or laptop may simply not be there - usually this can be found in some server solutions, OEM boards or products from second-tier vendors.

Conclusion

We found out what USB Legacy Support is, defined the purpose of this option, and looked at methods for enabling it in common BIOS or UEFI options.

Summary

Advice: Once the Secure Boot feature is disabled and Legacy Mode is enabled on computers with less than 2 terabyte hard drives, the UEFI partition can be completely removed at will (for example, if you no longer need to use Windows 8). This can be done with an application like Gparted).

Compatibility Mode Legacy Mode is an option that usually allows you to install and run operating systems that do not support UEFI. This applies to Windows 7 and earlier, as well as many smaller Linux distributions. By disabling UEFI, the computer will boot directly from the BIOS.

Although Manjaro supports UEFI out of the box, unless compatibility mode has been enabled, the friendly graphical boot screen provided in the installation instructions will not appear. Instead, a clumsy menu will appear. This menu is for UEFI.

Step 1: Access BIOS settings

Advice: There is no need to follow complex and confusing instructions developed by Windows 8 to access your BIOS or UEFI. You can also click on the images below to enlarge them..

UEFI is an add-on to your computer's BIOS. Thus, you need to go to the BIOS settings in order to disable the secure boot option in UEFI. To do this, press one of the function keys (F) - usually - immediately after turning on or rebooting the system. Key usually provides access directly to the UEFI system itself.

Once you get to the UEFI menu, an image similar to this will appear on the screen.

However, as shown, it is still possible to access the BIOS from here, in this case by pressing the .

When going to BIOS settings, a window similar to this will open.

Step 2: Accessing Download Settings

Getting into the BIOS settings, you will be able to use the arrow keys<влево>And<вправо>navigate through tabs (usually Main, Security, System Configuration And exit). Arrow keys can be used<вверх>or<вниз>to highlight and select the settings placed under each tab.

1. Navigate with arrows<влево> / <вправо>to the tab System Configuration.

2. A line will open Boot Options. Select it with arrows<вверх> / <вниз>.

3. With it highlighted, press<ввод>to get to her settings.

Step 3: Activate Legacy Mode

Attention: Again, if your hard drive is larger than 2 TB / 2000 GB, you should not enable Compatibility Mode. If Compatibility Mode is already disabled, then your BIOS may try to automatically enable it, enabling Secure Boot along the way.

While in Boot Options, you will see the settings Legacy Support / Mode.

1. Highlight an option Legacy Support / Mode using arrows<вверх> / <вниз>on keyboard.

2. With it highlighted, press<ввод>to enter the menu.

3. As you can see in the photo, a new menu will appear where you can select "Disabled" or "Enabled". Highlight Enabled clicking on the arrows<вверх> / <вниз>, then press<ввод>.

Hello dear readers! Today we will talk about one topic that is difficult at first glance, which will sound like this: UEFI Boot - what is it and how to disable UEFI in BIOS.

Of course, for a simple user, all these names and abbreviations do not mean anything, but nevertheless, when buying modern desktop computers and laptops, you will still come face to face with these concepts.

Yes, friends, this is the same settings section on a blue background, which you can enter at the very beginning when you turn on the computer. Here's a picture to refresh your memory:

Many more enthusiasts tried to play with the voltage and frequency of the main processor here in order to increase the power of their machine. So, the BIOS microprogram was replaced by another, more modern one.

And as you already understood, it is called UEFI. Among the new innovations, it can be noted support for high screen resolutions, very large disks and work with the mouse.

If you read all the lines above and did not understand anything at all, then watch a short video to reinforce the topic:

So, it should definitely be said that a full-fledged UEFI system is not yet implemented in all modern computers. But some of its new features, hitherto unseen, have been successfully implemented in the old BIOS shell.

And one of them, the so-called UEFI Boot (full name Secure Boot). The meaning of its work is to prevent the substitution of the system boot source, thereby reducing the use of unlicensed software.

That is, it turns out such a picture that now we will not be able to boot, for example, from a flash drive or a third-party disk. Indeed, in this situation, they simply will not be in the list of available devices:

But in fact, this problem can be solved very easily. To do this, you need to make a couple of settings and that's it. So let's get to work. So, enough of the theory.

And in order to disable UEFI functions in BIOS, you must immediately enter it. As mentioned above, for this you need to press a certain key combination immediately after turning on the computer.

Thus, we have disabled the main UEFI protection function from third-party bootloaders. Then you should go to the "Boot" section and set the parameters as in the screenshot below:

After that, we should have a list of available devices. Now by changing their position in the list, you can manipulate the download sources. Again, using the author's example, this can be done with a keyboard shortcut Fn+F5/F6:

Well, after all the parameters entered, it remains only to save the changes. This is done in the "Exit" menu by selecting the "Exit Saving Changes" item:

That's all, my friends, now you know for sure the answer to the question: UEFI Boot - what is it and how to disable UEFI in BIOS. If you still have questions, feel free to ask them in the comments.

Well, if you suddenly want to learn much about the UEFI BIOS, then watch a short video where this topic is covered more widely.