Legacy Boot is greyed out in BIOS [Fixed]

UEFI and Legacy are the two modes of BIOS. The UEFI mode of BIOS has several advantages over the Legacy BIOS mode. That’s why the Legacy BIOS mode has become less popular after the introduction of UEFI. Some of the advantages of UEFI include a faster booting process, support for the hard drives larger than 2 TB, secure boot, etc. The Legacy BIOS mode does not support secure boot. Hence, the computers with UEFI BIOS mode are more secure than those with Legacy BIOS mode. If your BIOS supports both Legacy and UEFI modes, you can switch between these two modes. But some users are unable to switch back to the Legacy BIOS mode after enabling the UEFI BIOS mode. When they tried to do so, they found the Legacy Boot is greyed out in BIOS. In this article, we will see why the Legacy Boot is greyed out in BIOS and what can be done to fix this problem.

Legacy Boot is greyed out in BIOS

There are multiple reasons why the Legacy Boot is greyed out in your system BIOS. The following suggestions will help you fix the problem. Before you proceed, if you are using Intel NUC products, you should check on its official website whether your model supports Legacy BIOS mode or not.

Disable Secure Boot
Change your chipset SATA mode
Disable Platform Trusted Technology (PTT)
Disable Modern Standby mode

Let’s see all these fixes in detail.

1] Disable Secure Boot

The most common reason why Legacy Boot is greyed out or why you are not able to switch from UEFI to Legacy is Secure Boot. Secure Boot is one of the features of UEFI (Unified Extensible Firmware Interface). Secure Boot ensures that the user’s system boots only by using the software trusted by OEM (Original Equipment Manufacturer). When you turn on your PC, the firmware checks for the valid signature of each piece of the boot software and the drivers. This prevents malware from taking control of your computer during the boot process.

Secure Boot is one of the requirements of UEFI. You cannot switch from Legacy BIOS mode to UEFI BIOS mode until you enable Secure Boot on your system. But if you want to switch back to the Legacy mode from UEFI, Secure Boot should be disabled on your device. Legacy Boot is not allowed if the Secure Boot is enabled on your device. If the Legacy Boot is greyed out in your system BIOS, disable Secure Boot. After doing that, you should be able to switch back to the Legacy BIOS mode.

2] Change your chipset SATA mode

If after disabling the Secure Boot, the Legacy Boot option is still greyed out, the thing that is preventing you from enabling the Legacy BIOS mode is your chipset SATA mode. If the SATA mode is set to Intel RST, you will no longer be able to switch from UEFI to Legacy BIOS mode. To resolve this issue, you have to switch your chipset SATA mode from Intel RST to RAID (if you want to use RAID) or AHCI (if you do not plan to use RAID). Before you proceed, we recommend you backup all your data on an external hard disk.

To switch your chipset SATA mode from Intel RST to RAID or AHCI without reinstalling Windows or losing data, you have to enter Safe Mode. Before doing so, make sure that you remember your Windows password, else you will not be able to enter normal mode from the Safe mode. We also recommend you disable BitLocker if you have enabled it. Also, save your BitLocker recovery key elsewhere or write it on paper. After performing the below-listed steps, you can re-enable BitLocker.

Follow the steps below:

Open Command Prompt as an administrator. Now, copy the following command and paste it into the Command Prompt. To paste it, simply right-click anywhere in the Command Prompt window. After that, hit Enter.

bcdedit /set {current} safeboot minimal

When you receive the “The operation completed successfully” message in Command Prompt, close the Command Prompt and restart your computer and enter in your system BIOS.

Now, change the SATA Controller mode from Intel RST to RAID or AHCI. Save the changes and exit the BIOS setup. Windows will automatically start in the Safe mode. Open Command Prompt as an administrator, copy the following command, and paste it into the Command Prompt. After that, hit Enter.

bcdedit /deletevalue {current} safeboot

When you see the message “The operation completed successfully,” close the Command prompt and restart your computer. Windows will boot in normal mode automatically.

The above process will enable the RAID or AHCI drivers in Windows. Now, you should be able to change the BIOS mode from UEFI to Legacy.

3] Disable Platform Trusted Technology (PTT)

If Intel PTT (Platform Trusted Technology) is enabled on your system, you will find the Legacy Boot option greyed out in your system BIOS. Check if your BIOS supports Intel PTT technology or not. Enter into your system BIOS and navigate to the Security tab or section. If your system supports PTT technology, you will see it there. If PTT is enabled, disable it. After disabling PTT, you should be able to turn on the Legacy BIOS mode.

4] Disable Modern Standby mode

If Modern Standby mode is enabled on your system, you cannot switch to Legacy BIOS mode. Modern Standby is a modern power mode in Windows computers. In Modern Standby mode, the screen of your system turns off after some time of inactivity but the background processes remain active. This power mode has both advantages and disadvantages. For example, if a background task is active, Windows will not go to sleep until the task gets completed, but it will drain a lot of battery.

According to Microsoft, disabling the Modern Standby mode via system BIOS settings will not take effect until you reinstall Windows. But there is one more way by which you can disable the Modern Standby mode. This method has worked for many users and we will explain this method below. Before you proceed, it is better to check if your system supports Modern Standby mode and which power mode is active on your system. If the Legacy Standby mode (S3 mode) is already activated on your system, you need not perform the below steps. If your system is in Modern Standby mode, you will see the “Standby (S0 Low Power Idle) Network Connected” message in the Command Prompt.

Follow the instructions written below:

Open the Run command box by pressing the Win + R keys. Type regedit and click OK. Click Yes in the UAC prompt. This will open the Registry Editor.

Copy the following path, paste it into the address bar of the Registry Editor, and hit Enter.

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Power

Make sure that you have selected the Power key on the left side. Check if the PlatformAoAcOverride value exists on the right side or not. If not, you have to create it manually. For this, right-click on the empty space on the right side and go to “New > DWORD (32-bit) Value.” Right-click on the newly created value and select Rename. Name it as PlatformAoAcOverride and click OK.

Now, double-click on the newly created PlatformAoAcOverride value. It should show 0 in its Value Data. If not, enter 0 and click OK. Restart your computer to apply changes.

If you do not want to edit the Registry, you can follow the method described below to disable the Modern Standby mode on your Windows PC.

Disable Modern Standby mode via Command Prompt

If you have already disabled the Modern Standby mode via the Registry Editor, you need not do it again via the Command Prompt. Go through the following instructions to disable Modern Standby mode via Command Prompt:

Open Command Prompt as an administrator. Now, copy the following command and paste it into the Command Prompt. After that, hit Enter.

reg add HKLM\System\CurrentControlSet\Control\Power /v PlatformAoAcOverride /t REG_DWORD /d 0

Wait till the above command is executed successfully. After that, the Modern Standby mode will be disabled. After disabling the Modern Standby mode, you should be able to switch to the Legacy Boot mode in your BIOS.

Read: Fix Boot Device Not Found error in Windows 11/10.

How do I enable Legacy Boot in BIOS?

An option to change the Boot mode in BIOS is available under the BOOT tab or section. Enter your system BIOS and navigate to the BOOT tab. Now, highlight the UEFI/BIOS Boot mode option by using the arrow keys and press Enter to view the UEFI and Legacy options. After that, highlight the Legacy option using the arrow keys and hit Enter. Now, press the F10 key to save changes and exit BIOS.

You may find the option to change BIOS mode greyed out. This usually happens if:

The Secure Boot is enabled on your system.
Your chipset SATA mode is set to Intel RST.
The Platform Trusted Technology (PTT) is enabled on your system.
The Modern Standby mode is enabled on your system.

To resolve this issue, you have to disable the Secure Boot, disable the PTT, change the power mode from Modern Standby to Legacy Standby, and switch your chipset SATA mode from Intel RST to RAID or AHCI.

Hope this helps.

How do I fix Legacy Boot not supported?

You will get the “Legacy boot not supported” message if your hard disk partition is set to GPT. UEFI BIOS mode uses the GPT partition, whereas Legacy mode uses the MBR partition. Therefore, if your hard disk has a GPT partition style, you will not be able to enable Legacy Boot mode. To resolve this issue, convert the GPT partition style into MBR.