Windows boot loader dual boot

If you have a modern computer where Windows 7 Setup halts at boot time when displaying OS logo, then you need to apply the patch for Windows 7 UEFI loader in FlashBoot Pro. This patch provides emulation of VGA BIOS (INT 10H) over UEFI GOP framebuffer, thus enabling installation and use of Windows 7 on the modern purely UEFI-based computers without CSM.

And if you have a dual-boot configuration of Windows 10/11 and Windows 7, you need to have two UEFI loaders simultaneously: a new one, capable of booting Windows 10/11 (with modern features, frequently updated by Windows Update); and older one, dedicated for booting Windows 7, patched by FlashBoot Pro for VGA BIOS emulation (thus, Windows Update preferrably should leave it alone).

This article explains in detail how to establish such a dual-boot configuration.

1. Problem statement

When there’s a single EFI System Partition, Windows 7 and Windows 10/11 have a conflict
over two file objects in that partition, that must be resolved somehow:

• UEFI bootloader (\EFI\Microsoft\Boot\bootmfgw.efi with .mui localizations): either
  patched for Windows 7 VGA emulation or with new features to boot Windows 10/11.
• Registry hive with Boot Configuration Data (\EFI\Microsoft\Boot\BCD with .LOG1 and
  .LOG2 integrity logs): is it for Windows 10/11 or for Windows 7, and if for both,
  then how to make multiple UEFI loaders (if there are multiple UEFI loaders in
  the single EFI System Partition) not to display boot menu with two options.

2. Simple workaround

If form factor of your device allows multiple internal storage devices (such as SSDs and HDDs),
e.g. if this is not a tablet, sealed down by a glue, then install Windows 7 and Windows 10/11
to a different physical storage devices (in any order, but please temporarily disconnect bootable
storage with first OS before installing second OS, so Setup of the second OS won’t find
EFI System Partition prepared by Setup of the first OS and won’t mess with it).

After the installation, you will have two EFI system partitions and so you can choose OS
(storage device) to boot from in the boot menu provided by UEFI firmware of your computer.

3. Solution for hard cases

If you must have single bootable physical storage device and so single EFI system partition
(because your tablet does not allow disassembly/teardown, or your laptop does not have a bay
for second storage device), then there’s a harder way (but it’s still possible):

1. Erase all partitions on that storage device, make sure it has GPT layout.
2. Reserve 500 Mb for EFI system partition (create data partition).
3. Install Windows 7 and let it create its own EFI System Partition (100 Mb) ahead of
   Windows Partition, and leave some unpartitioned space for Windows 10/11.
4. Format empty FAT32 filesystem in 500 Mb reserved data partition.
5. Install rEFInd bootloader
   to 500 Mb reserved data partition.
6. Change Type GUID for 100 Mb EFI system partition from
   C12A7328-F81F-11D2-BA4B-00A0C93EC93B (EFI system partition) to
   EBD0A0A2-B9E5-4433-87C0-68B6B72699C7 (basic data partition).
7. Change Type GUID for 500 Mb reserved data partition from
   EBD0A0A2-B9E5-4433-87C0-68B6B72699C7 (basic data partition) to
   C12A7328-F81F-11D2-BA4B-00A0C93EC93B (EFI system partition).
8. Reboot, make sure that rEFInd works, Windows 7 UEFI Loader is detected by rEFInd,
   and Windows 7 still boots OK.
9. Install Windows 10/11 from USB thumbdrive as usually. It will hijack 500 Mb EFI System
   Partition for itself, and insert its own UEFI loader ahead of rEFInd in the UEFI boot order,
   but otherwise it will work OK.
10. Restore previous boot order: rEFInd ahead of Windows 10/11 UEFI loader.
    Now rEFInd should detect both Windows 10/11 and Windows 7 and offer a choice
    between these operating systems. Windows 10/11 and its UEFI loader has full
    control over 500 Mb EFI System Partition, and Windows 7 UEFI loader is
    located in separate 100 Mb data partition (former EFI System Partition)
    but still works OK.

Then Windows 7 will have its own kinda-sorta EFI System Partition (actually,
it’s just bootable data partition), with its own separate UEFI loader and BCD hive,
and Windows 10/11 and its Setup and its Windows Update will leave this partition
and patched Windows 7 UEFI loader alone.

4. Other dual-boot considerations

Please be aware that in dual-boot configurations of Windows 10/11 and Windows 7, CheckDisk
may kick in on every reboot of Windows 7. This is totally unrelated to the aforementioned
UEFI boot shenanigans, and happens on CSM/Legacy systems too. Why it happens and what can
be done about it, please
read in the separate article (in short: a small registry tweak in Windows 10/11 is necessary
to make it use old format of NTFS log compatible with Windows 7 and its CheckDisk).

5. Questions and answers

Q: How to change Type GUIDs for partitions?

A: Most convenient way is to use
Emergency Boot Kit,
see User Guide
for Partition Manager: pages 36, 37, 39 and 40 demonstate this process step-by-step.
If you do not have a paid version of Emergency Boot Kit, you can do this for free in a
live Linux distribution like SLAX: run lsblk command to list
all block devices, then run fdisk -l /dev/sda,
fdisk -l /dev/sdb, fdisk -l /dev/mmcblk1
etc (substitute your block device name after /dev as necessary)
to determine which Linux block device is your main internal bootable storage device,
then run fdisk -l /dev/(chosen_device_name) to start
editing partition table, then p subcommand to print partition
table, thent subcommand to change partitition type, then
1 for «EFI system» type or 11
for «basic data» type, then w subcommand to write
altered partition table to the disk. Alternatively, q subcommand
exits fdisk program without saving altered partition table to the disk.

Q: How to change UEFI boot order?

A: Most convenient way is via the UEFI firmware setup utility, but that depends on
UEFI firmware vendor (consult user manual for your motherboard or laptop). Also there is
a vendor-neutral method of changing UEFI boot order: using efibootmgr
tool in live Linux distribution like SLAX. When run without parameters,
efibootmgr displays current boot order (list of comma-separated
numbers) and a table below (which explains a meaning of each number: for example, an OS name,
or PXE network boot device name, or rEFInd boot loader name or whatever). Then you can run
efibootmgr —bootorder XXXX,YYYY,ZZZZ,… with reordered list
of the same comma-separated numbers. In such way boot order will be changed by
efibootmgr and written into the UEFI configuration
variables in the NVRAM.

This is an article detailing different methods of Arch/Windows coexistence.

Important information

Windows UEFI vs BIOS limitations

Microsoft imposes limitations on which firmware boot mode and partitioning style can be supported based on the version of Windows used:

Note: The following points only list configurations supported by the Windows Setup even though Windows itself may still work on these unsupported configurations. A good example of this is Windows 11 which still works on a BIOS/MBR configuration once the Windows Setup check is bypassed.

• Windows 8/8.1 and 10 x86 32-bit support booting in IA32 UEFI mode from GPT disk only, OR in BIOS mode from MBR disk only. They do not support x86_64 UEFI boot from GPT/MBR disk, x86_64 UEFI boot from MBR disk, or BIOS boot from GPT disk. On market, the only systems known to ship with IA32 (U)EFI are some old Intel Macs (pre-2010 models?) and Intel Atom System-on-Chip (Clover trail and Bay Trail) Windows Tablets, which boot ONLY in IA32 UEFI mode and ONLY from GPT disk.
• Windows 8/8.1 and 10 x86_64 versions support booting in x86_64 UEFI mode from GPT disk only, OR in BIOS mode from MBR disk only. They do not support IA32 UEFI boot, x86_64 UEFI boot from MBR disk, or BIOS boot from GPT disk.
• Windows 11 only supports x86_64 and a boot in UEFI mode from GPT disk.

In case of pre-installed Systems:

• All systems pre-installed with Windows XP, Vista or 7 32-bit, irrespective of Service Pack level, bitness, edition (SKU) or presence of UEFI support in firmware, boot in BIOS/MBR mode by default.
• MOST of the systems pre-installed with Windows 7 x86_64, irrespective of Service Pack level, bitness or edition (SKU), boot in BIOS/MBR mode by default. Very few late systems pre-installed with Windows 7 are known to boot in x86_64 UEFI/GPT mode by default.
• ALL systems pre-installed with Windows 8/8.1, 10 and 11 boot in UEFI/GPT mode. Up to Windows 10, the firmware bitness matches the bitness of Windows, ie. x86_64 Windows boot in x86_64 UEFI mode and 32-bit Windows boot in IA32 UEFI mode.

An easy way to detect the boot mode of Windows is to do the following[1]:

• Boot into Windows
• Press Win+R keys to start the Run dialog
• In the Run dialog type msinfo32 and press Enter
• In the System Information windows, select System Summary on the left and check the value of BIOS mode item on the right
• If the value is UEFI, Windows boots in UEFI/GPT mode. If the value is Legacy, Windows boots in BIOS/MBR mode.

In general, Windows forces type of partitioning depending on the firmware mode used, i.e. if Windows is booted in UEFI mode, it can be installed only to a GPT disk. If Windows is booted in Legacy BIOS mode, it can be installed only to an MBR disk. This is a limitation enforced by Windows Setup, and as of April 2014 there is no officially (Microsoft) supported way of installing Windows in UEFI/MBR or BIOS/GPT configuration. Thus Windows only supports either UEFI/GPT boot or BIOS/MBR configuration.

Tip: Windows 10 version 1703 and newer supports converting from BIOS/MBR to UEFI/GPT using MBR2GPT.EXE.

Such a limitation is not enforced by the Linux kernel, but can depend on which boot loader is used and/or how the boot loader is configured. The Windows limitation should be considered if the user wishes to boot Windows and Linux from the same disk, since installation procedure of boot loader depends on the firmware type and disk partitioning configuration. In case where Windows and Linux dual boot from the same disk, it is advisable to follow the method used by Windows, ie. either go for UEFI/GPT boot or BIOS/MBR boot. See https://support.microsoft.com/kb/2581408 for more information.

Boot loader UEFI vs BIOS limitations

Most of the Linux boot loaders installed for one firmware type cannot launch or chainload boot loaders of the other firmware type. That is, if Arch is installed in UEFI/GPT or UEFI/MBR mode in one disk and Windows is installed in BIOS/MBR mode in another disk, the UEFI boot loader used by Arch cannot chainload the BIOS installed Windows in the other disk. Similarly if Arch is installed in BIOS/MBR or BIOS/GPT mode in one disk and Windows is installed in UEFI/GPT in another disk , the BIOS boot loader used by Arch cannot chainload UEFI installed Windows in the other disk.

The only exceptions to this are GRUB in Apple Macs in which GRUB in UEFI mode can boot BIOS installed OS via appleloader command (does not work in non-Apple systems), and rEFInd which technically supports booting legacy BIOS OS from UEFI systems, but does not always work in non-Apple UEFI systems as per its author Rod Smith.

However if Arch is installed in BIOS/GPT in one disk and Windows is installed in BIOS/MBR mode in another disk, then the BIOS boot loader used by Arch can boot the Windows in the other disk, if the boot loader itself has the ability to chainload from another disk.

Note: To dual-boot with Windows on same disk, Arch should follow the same firmware boot mode and partitioning combination used by the Windows installation.

Windows Setup creates a 100 MiB EFI system partition (except for Advanced Format 4K native drives where it creates a 300 MiB ESP), so multiple kernel usage is limited. Workarounds include:

• If you are installing Windows from scratch, you can dictate the size of the EFI system partition during installation. See #The EFI system partition created by Windows Setup is too small
• Mount ESP to /efi and use a boot loader that has file system drivers and is capable of launching kernels that reside on other partitions.
• Reduce the size of the Windows partition and replace the existing ESP with a new, larger one.
• Backup and delete unneeded fonts in esp/EFI/Microsoft/Boot/Fonts/ [2].
• Backup and delete unneeded language directories in esp/EFI/Microsoft/Boot/ (e.g. to only keep en-US).
• Use a higher, but slower, compression for the initramfs images making sure to decompress the loadable kernel modules and firmware. E.g.

COMPRESSION="xz"
COMPRESSION_OPTIONS=(-9e)
MODULES_DECOMPRESS="yes"

UEFI Secure Boot

All pre-installed Windows 8/8.1, 10 and 11 systems by default boot in UEFI/GPT mode and have UEFI Secure Boot enabled by default. This is mandated by Microsoft for all OEM pre-installed systems.

Arch Linux install media does not support Secure Boot yet. See Secure Boot#Booting an installation medium.

It is advisable to disable UEFI Secure Boot in the firmware setup manually before attempting to boot Arch Linux. Windows 8/8.1, 10 and 11 SHOULD continue to boot fine even if Secure boot is disabled. The only issue with regards to disabling UEFI Secure Boot support is that it requires physical access to the system to disable secure boot option in the firmware setup, as Microsoft has explicitly forbidden presence of any method to remotely or programmatically (from within OS) disable secure boot in all Windows 8/8.1 and above pre-installed systems

Fast Startup and hibernation

There are two OSs that can be hibernated, you can hibernate Windows and boot Linux (or another OS), or you can hibernate Linux and boot Windows, or hibernate both OSs.

Warning: Data loss can occur if Windows hibernates and you dual boot into another OS and make changes to files on a filesystem (such as NTFS) that can be read and written to by Windows and Linux, and that has been mounted by Windows [3]. Similarly, data loss can occur if Linux hibernates, and you dual boot into another OS etc. Windows may hibernate even when you press shutdown, see section #Windows settings.

For the same reason, if you share one EFI system partition between Windows and Linux, then the EFI system partition may be damaged if you hibernate (or shutdown with Fast Startup enabled) Windows and then start Linux, or hibernate Linux and then start Windows.

ntfs-3g added a safe-guard to prevent read-write mounting of hibernated NTFS filesystems, but the NTFS driver within the Linux kernel has no such safeguard.

Windows cannot read filesystems such as ext4 by default that are commonly used for Linux. These filesystems do not have to be considered, unless you install a Windows driver for them.

Windows settings

Fast Startup is a feature in Windows 8 and above that hibernates the computer rather than actually shutting it down to speed up boot times.

There are multiple options regarding the Windows settings for Fast Startup and hibernation that are covered in the next sections.

• disable Fast Startup and disable hibernation
• disable Fast Startup and enable hibernation
• enable Fast Startup and enable hibernation

The procedure of disabling Fast Startup is described in the tutorials for Windows 8, Windows 10 and Windows 11. In any case if you disable a setting, make sure to disable the setting and then shut down Windows, before installing Linux; note that rebooting is not sufficient.

Disable Fast Startup and disable hibernation

This is the safest option, and recommended if you are unsure about the issue, as it requires the least amount of user awareness when rebooting from one OS into the other. You may share the same EFI system partition between Windows and Linux.

In a Windows command-line shell with administrator privileges:

> powercfg /H off

Disable Fast Startup and enable hibernation

This option requires user awareness when rebooting from one OS into the other.
If you want to start Linux while Windows is hibernated, which is a common use case, then

• you must use a separate EFI system partition (ESP) for Windows and Linux, and ensure that Windows does not mount the ESP used for Linux. As there can only be one ESP per drive, the ESP used for Linux must be located on a separate drive than the ESP used for Windows. In this case Windows and Linux can still be installed on the same drive in different partitions, if you place the ESP used by linux on another drive than the Linux root partition.
• you can not read-write mount any filesystem in Linux, that is mounted by Windows while Windows is hibernated. You should be extremely careful about this, and also consider Automount behaviour.
• If you shut down Windows fully, rather than hibernating, then you can read-write mount the filesystem.

Note: You can avoid this issue for a drive by mounting a drive as an external drive in Windows and ejecting the drive in Windows before hibernating.

Enable Fast Startup and enable hibernation

The same considerations apply as in case «Disable Fast Startup and enable hibernation», but since Windows can not be shut down fully, only hibernated, you can never read-write mount any filesystem that was mounted by Windows while Windows is hibernated.

Note: Windows updates may re-enable Fast Startup, as reported in [4]^{[dead link 2024-07-30 ⓘ]}.

Windows filenames limitations

Windows is limited to filepaths being shorter than 260 characters.

Windows also puts certain characters off limits in filenames for reasons that run all the way back to DOS:

• < (less than)
• > (greater than)
• : (colon)
• " (double quote)
• / (forward slash)
• \ (backslash)
• | (vertical bar or pipe)
• ? (question mark)
• * (asterisk)

These are limitations of Windows and not NTFS: any other OS using the NTFS partition will be fine. Windows will fail to detect these files and running chkdsk will most likely cause them to be deleted. This can lead to potential data-loss.

NTFS-3G applies Windows restrictions to new file names through the windows_names option: ntfs-3g(8) § Windows_Filename_Compatibility (see fstab).

Installation

The recommended way to set up a Linux/Windows dual booting system is to first install Windows, only using part of the disk for its partitions. When you have finished the Windows setup, boot into the Linux install environment where you can create and resize partitions for Linux while leaving the existing Windows partitions untouched. The Windows installation will create the EFI system partition which can be used by your Linux boot loader. If you are installing Windows from scratch, do note that the EFI System partition created by Windows Setup will be too small for most use cases. See #The EFI system partition created by Windows Setup is too small.

Windows before Linux

BIOS systems

Using a Linux boot loader

You may use any multi-boot supporting BIOS boot loader.

Using the Windows Vista/7/8/8.1 boot loader

This section explains how to:

• install a linux boot loader on a partition instead of the MBR;
• copy this boot loader to a partition readable by the Windows boot loader;
• use the windows boot loader to start said copy of the linux boot loader.

Note: Some documents state that the partition being loaded by the Windows boot loader must be a primary partition but usage of an extended partition has been documented as working.

• When installing the boot loader, install it on your /boot partition rather than the MBR. For details on doing this with GRUB, see GRUB/Tips and tricks#Install to partition or partitionless disk, for Syslinux, see the note at Syslinux#Manually, for LILO see LILO#Install to partition or partitionless disk.

• Make a copy of the VBR:

  dd if=/dev/disk of=/path/to/linux.bin bs=512 count=1

  where /dev/disk is the path of the partition on which your boot loader is installed and /path/to/ is the mounted filesystem on which you want the copy to be readable by the Windows boot loader.

• On Windows, the linux.bin file should now be accessible. Run cmd with administrator privileges (navigate to Start > All Programs > Accessories, right-click on Command Prompt and select Run as administrator):

  bcdedit /create /d "Linux" /application BOOTSECTOR

  BCDEdit will return a UUID for this entry. This will be referred to as UUID in the remaining steps.

  bcdedit /set UUID device partition=c: (or the drive letter on which linux.bin is kept)
  bcdedit /set UUID path \path\to\linux.bin
  bcdedit /displayorder UUID /addlast
  bcdedit /timeout 30

On reboot, both Windows and Linux should now show up in the Windows boot loader.

Note: On some hardware, the Windows boot loader is used to start another OS with a second power button (e.g. Dell Precision M4500).

For more details, see https://www.iceflatline.com/2009/09/how-to-dual-boot-windows-7-and-linux-using-bcdedit/

UEFI systems

If you already have Windows installed, it will already have created some partitions on a GPT-formatted disk:

• a Windows Recovery Environment partition, generally of size 499 MiB,
• an EFI system partition with a FAT32 filesystem, containing the Windows Boot Manager,
• a Microsoft Reserved Partition, generally of size 128 MiB,
• a Microsoft basic data partition with a NTFS filesystem, which corresponds to C:,
• potentially system recovery and backup partitions and/or secondary data partitions (corresponding often to D: and above).

Using the Disk Management utility in Windows, check how the partitions are labelled and which type gets reported. The Reserved Partition may not be visible in the Disk Management utility in which case it can be identified using diskpart in windows cmd. This will help you understand which partitions are essential to Windows, and which others you might repurpose. The Windows Disk Management utility can also be used to shrink Windows (NTFS) partitions to free up disk space for additional partitions for Linux.

Warning: The first 4 partitions in the above list are essential, do not delete them.

You can then proceed with partitioning, depending on your needs. The boot loader needs to support chainloading other EFI applications to dual boot Windows and Linux. An additional EFI system partition should not be created, as it may prevent Windows from booting.

Note: It only appears when Linux is installed on the second hard disk and a new EFI system partition is created on the second hard disk.

Simply mount the existing partition.

Computers that come with newer versions of Windows often have Secure Boot enabled. You will need to take extra steps to either disable Secure Boot or to make your installation media compatible with secure boot (see above and in the linked page).

Linux before Windows

Even though the recommended way to set up a Linux/Windows dual booting system is to first install Windows, it can be done the other way around. In contrast to installing Windows before Linux, you will have to set aside a partition for Windows, say 40GB or larger, in advance. Or have some unpartitioned disk space, or create and resize partitions for Windows from within the Linux installation, before launching the Windows installation.

UEFI firmware

Windows will use the already existing EFI system partition.
Follows an outline, assuming Secure Boot is disabled in the firmware.

1. Boot into windows installation. Watch to let it use only the intended partition, but otherwise let it do its work as if there is no Linux installation.
2. Follow the #Fast Startup and hibernation section.
3. Fix the ability to load Linux at start up, perhaps by following #Cannot boot Linux after installing Windows. It was already mentioned in #UEFI systems that some Linux boot managers will autodetect Windows Boot Manager. Even though newer Windows installations have an advanced restart option, from which you can boot into Linux, it is advised to have other means to boot into Linux, such as an arch installation media or a live CD.

Windows 10 with GRUB

The following assumes GRUB is used as a boot loader (although the process is likely similar for other boot loaders) and that Windows 10 will be installed on a GPT block device with an existing EFI system partition (see the «System partition» section in the Microsoft documentation for more information).

Create with program gdisk on the block device the following three new partitions. See [5] for more precise partition sizes.

Create NTFS file systems on the new Microsoft basic data and Windows RE (recovery) partitions using the mkntfs program from package ntfs-3g.

Reboot the system into a Windows 10 installation media. When prompted to install select the custom install option and install Windows on the Microsoft basic data partition created earlier. This should also install Microsoft EFI files in the EFI system partition.

After installation (set up of and logging into Windows not required), reboot into Linux and generate a GRUB configuration for the Windows boot manager to be available in the GRUB menu on next boot.

Troubleshooting

Couldn’t create a new partition or locate an existing one

See #Windows UEFI vs BIOS limitations.

Cannot boot Linux after installing Windows

See Unified Extensible Firmware Interface#Windows changes boot order.

Restoring a Windows boot record

By convention (and for ease of installation), Windows is usually installed on the first partition and installs its partition table and reference to its boot loader to the first sector of that partition. If you accidentally install a boot loader like GRUB to the Windows partition or damage the boot record in some other way, you will need to use a utility to repair it. Microsoft includes a boot sector fix utility FIXBOOT and an MBR fix utility called FIXMBR on their recovery discs, or sometimes on their install discs. Using this method, you can fix the reference on the boot sector of the first partition to the boot loader file and fix the reference on the MBR to the first partition, respectively. After doing this you will have to reinstall GRUB to the MBR as was originally intended (that is, the GRUB boot loader can be assigned to chainload the Windows boot loader).

If you wish to revert back to using Windows, you can use the FIXBOOT command which chains from the MBR to the boot sector of the first partition to restore normal, automatic loading of the Windows operating system.

Of note, there is a Linux utility called ms-sys^AUR that can install MBR’s. However, this utility is only currently capable of writing new MBRs (all OS’s and file systems supported) and boot sectors (a.k.a. boot record; equivalent to using FIXBOOT) for FAT file systems. Most LiveCDs do not have this utility by default, so it will need to be installed first, or you can look at a rescue CD that does have it, such as Parted Magic.

First, write the partition info (table) again by:

# ms-sys --partition /dev/sda1

Next, write a Windows 2000/XP/2003 MBR:

# ms-sys --mbr /dev/sda  # Read options for different versions

Then, write the new boot sector (boot record):

# ms-sys -(1-6)          # Read options to discover the correct FAT record type

ms-sys can also write Windows 98, ME, Vista, and 7 MBRs as well, see ms-sys -h.

Restoring an accidentally deleted EFI system partition

If you have a GPT-partitioned disk and erased (e.g. with mkfs.fat -F32 /dev/sdx) the EFI system partition, you will notice that Windows Boot Manager will either disappear from your boot options, or selecting it will send you back to the UEFI.

To remedy it, boot with a Windows installation media, press Shift+F10 to open the console (or click NEXT > Repair Computer > Troubleshoot… > Advanced > Command Prompt), then start the diskpart utility:

X:\Sources> diskpart
DISKPART> list disk

Select the appropriate hard drive by typing:

DISKPART> select disk number

Make sure that there is a partition of type system (the EFI system partition):

DISKPART> list partition

Select this partition:

DISKPART> select partition number

and assign a temporary drive letter to it:

DISKPART> assign letter=G:

DiskPart successfully assigned the drive letter or mount point.

To make sure that drive letter is correctly assigned:

DISKPART> list vol

 Volume ###  Ltr  Label        Fs     Type        Size     Status     Info
 ----------  ---  -----------  -----  ----------  -------  ---------  --------
 Volume 0     E                       DVD-ROM         0 B  No Media
 Volume 1     C                NTFS   Partition    195 GB  Healthy    Boot
 Volume 2         WINRE        NTFS   Partition    400 MB  Healthy    Hidden
 Volume 3     G                FAT32  Partition    499 MB  Healthy    System

Close diskpart:

DISKPART> exit

Navigate to C:\ (or what your system drive letter is):

X:\Sources> cd /d C:\

Next is the «magic» command, which recreate the BCD store (with /s for the mount point, /f for firmware type, optionally add /v for verbose):

C:\> bcdboot C:\Windows /s G: /f UEFI

Tip: If it hangs up after a minute, hit Ctrl+c. This happens sometimes, but you will get a message like boot files successfully created and it will have worked just fine.

You should now have Windows Boot Manager working as a boot option, and thus have access to Windows. Just make sure to never format your EFI system partition again!

Note: Remove the drive letter G assigned to the EFI system partition to keep it from showing up in My Computer.

See [6], [7] and [8].

The EFI system partition created by Windows Setup is too small

By default, Windows Setup creates a 100 MiB EFI system partition (except for Advanced Format 4K native drives where it creates a 300 MiB ESP). This is generally too small to fit everything you need. You can replace the existing EFI system partition with a new, larger one.

If you are installing Windows from scratch, you can dictate the size of the EFI system partition during installation[9]:

1. Select your installation target and make sure it has no partitions.
2. Click New and then the Apply buttons. The Windows installer will then generate the expected partitions (allocating nearly everything to its primary partition) and just 100MB to the EFI.
3. Use the UI to delete the System, MSR, and Primary partitions. Leave the Recovery partition (if present) alone.
4. Press Shift+F10 to open the Command Prompt.
5. Type diskpart.exe and press Enter to open the disk partitioning tool.
6. Type list disk and press Enter to list your disks. Find the one you intend to modify and note its disk number.
7. Type select disk disk_number with the disk number to modify.
8. Type create partition efi size=size with the desired size of the ESP in Mebibytes (MiB), and press Enter. See the note at EFI system partition#Create the partition for the recommended sizes.
9. Type format quick fs=fat32 label=System and press Enter to format the ESP
10. Type exit and press Enter to exit the disk partitioning tool and exit followed by Enter again.

Once Windows is installed, you can resize the primary partition down within Windows and then reboot and go about your usual Arch install, filling the space you just created.

Alternatively, you can use the Arch install media to create a single EFI system partition of your preferred size before you install Windows on the drive. Windows Setup will use the EFI system partition you made instead of creating its own.

Unable to install Windows Cumulative Update on BIOS system

On BIOS systems, Windows cumulative updates may fail with the error We couldn’t complete the updates. Undoing changes. Don’t turn off your computer. In such case, while in Windows, you need to set the Windows partition as active.

C:\> diskpart
DISKPART> list disk
DISKPART> select disk number
DISKPART> list partition
DISKPART> select partition number
DISKPART> active
DISKPART> exit

After successfully installing the Windows update, mark back your Linux partition as active, using the commands above.

Note: Setting a partition as active in the diskpart tool in Windows has the same effect as setting the boot flag in GParted.

Time standard

• Recommended: Set both Arch Linux and Windows to use UTC, following System time#UTC in Microsoft Windows. Some versions of Windows revert the hardware clock back to localtime if they are set to synchronize the time online. This issue appears to be fixed in Windows 10.
• Not recommended: Set Arch Linux to localtime and disable all time synchronization daemons. This will let Windows take care of hardware clock corrections and you will need to remember to boot into Windows at least two times a year (in Spring and Autumn) when DST kicks in. So please do not ask on the forums why the clock is one hour behind or ahead if you usually go for days or weeks without booting into Windows.

Bluetooth pairing

When it comes to pairing Bluetooth devices with both the Linux and Windows installation, both systems have the same MAC address, but will use different link keys generated during the pairing process. This results in the device being unable to connect to one installation, after it has been paired with the other. To allow a device to connect to either installation without re-pairing, follow Bluetooth#Dual boot pairing.

See also

• Booting Windows from a desktop shortcut
• One-time boot into Windows partition from desktop shortcut
• Windows 7/8/8.1/10 ISO to Flash Drive burning utility for Linux (MBR/GPT, BIOS/UEFI, FAT32/NTFS)

Can we dual-boot Windows 10 and Windows 11? Yes, we can! And dual-booting Windows 10 and Windows 11 can be quite helpful if you need to work with both operating systems. It’s also a good choice if you want to see what Windows 11 is all about, but you don’t want to let go of your old Windows 10 setup. Whatever your reasons are, in this article, we’re going to guide you through the steps of installing Windows 10 and Windows 11 in a dual-boot configuration. So, if you want to know all the details on how to dual boot Windows 11 with Windows 10 on the same computer, read on:

NOTE: For the purpose of this tutorial, we’re going to show you how to dual boot Windows 10 and Windows 11 when you first install Windows 10, and afterward, you install Windows 11. However, keep in mind that the other way around is also possible (install Windows 11 first and Windows 10 second), and the steps are exactly the same.

1. Install Windows 10

The first step to dual-boot Windows 10 and Windows 11 is to have Windows 10 installed on your PC. If you’re already running Windows 10, skip to the next step of this guide. Otherwise, if you have a new computer with no operating system on it or you simply want to start from zero for a completely clean experience, first install Windows 10. We’ve covered all the necessary steps in detail in this separate tutorial: How to install Windows 10 from DVD, ISO, or USB. In short, what you need to do is create a Windows 10 installation USB memory stick or DVD, boot from it, and follow the instructions of the Windows 10 setup wizard.

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Installing Windows 10

2. Prepare a partition for Windows 11

When you have Windows 10 up and running on your computer, the next step you must take to dual boot with Windows 11 is to prepare a partition for the latter. There are two ways to do that:

• Shrink your Windows 10 partition, if the drive containing it is large enough to hold both operating systems
• Ensure that you have another partition or drive with enough free space on it, available to install Windows 11 on it

Let’s see how both methods work:

2.1. Shrink your Windows 10 partition

If you want to use the same partition on which Windows 10 is installed, you need to shrink it in order to have enough space to create a new partition for Windows 11. In case you don’t know how to do that, this tutorial explains everything in detail: 2 ways to resize a partition in Windows (all versions). However, if time is of the essence, here’s the condensed explanation of the steps you should take:

Open Disk Management — right-click on the Start button and select Disk Management from the WinX menu. Then, right-click on your Windows 10 partition and choose Shrink Volume from the contextual menu.

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Shrink volume reduces the size of the Windows 10 partition

In the Shrink C: dialog box, enter the number of megabytes you want to shrink the Windows 10 partition by. Make sure that you choose a value that’s large enough for Windows 11, which requires at least 64GB (65,536MB) of free space. Once done, press the Shrink button.

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Specifying the size to shrink the Windows 10 partition

After the shrinking is done, it’s time to create a new partition for Windows 11. Right-click on the Unallocated space on your drive and select New Simple Volume from the context menu.

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Creating a new partition for Windows 11

Follow the wizard’s steps and, when you get to the Format Partition settings, make sure you choose NTFS.

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Format the Windows 11 partition using NTFS

TIP: For more help, read this guide: 2 ways to create a partition in Windows (all versions).

Once you’ve created the partition for Windows 11, follow the instructions from the third chapter of this guide.

2.2. Choose another empty drive or partition on your PC

You may want to install Windows 10 and Windows 11 in dual-boot on different drives, or you already have a partition on your PC that you want to use for Windows 11. In this case, make sure that you don’t have any data on it. If you do, move the files you want to keep to another storage unit before installing Windows 11 or you risk losing them. Then, move on to the next step:

3. Install Windows 11

Now comes one of the essential steps of dual-booting Windows 10 with Windows 11: actually installing Windows 11. If you don’t already have a Windows 11 installation media, create one now, and use it to boot your Windows 10 computer. For instructions on how to do that, follow the steps from this guide: How to install Windows 11 from USB, DVD, or ISO.

After you boot your PC using the Windows 11 installation media, follow the wizard’s steps like you normally would, right until you get to the “Where do you want to install Windows?” question. When you get there, be very careful to select the partition you’ve prepared for Windows 11, as explained in the second step of this guide. Then, press Next and continue installing Windows 11 and configuring it as you like.

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Selecting the Windows 11 partition

4. Dual boot Windows 10 and Windows 11

Once you finish installing Windows 11, your computer is ready to dual-boot. Whenever you start or restart your PC, you’ll be asked what operating system you want to boot into: Windows 10 or Windows 11.

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The boot loader allows you to dual boot Windows 10 and Windows 11

Congratulations! You’re now dual-booting Windows 10 and Windows 11! 🙂

Additional configuration: How to set the default operating system for dual boot (Windows 10 or Windows 11)

Finally, there’s one more thing you might want to do for your dual-boot configuration: choose the default operating system and, maybe, the timeout of the “Choose an operating system” boot loader screen. That is because, after the standard 30 seconds, the boot loader automatically starts the default operating system. To set these as you want, open the System Configuration tool: search for msconfig and press the System Configuration result.

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Opening System Configuration

In the System Configuration window, select the Boot tab, and you should see Windows 10 and Windows 11 listed as dual-boot options. Click or tap the one you want as default and, if it’s not already the default choice, press the Set as default button.

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Set the default operating system

If you want to increase or decrease the display time of the boot loader, enter the number of seconds you prefer in the Timeout field on the right.

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Choose the timeout for the boot loader

Press OK to save your changes and close System Configuration. Then, reboot your computer to see how you like them.

Why did you want to dual boot Windows 10 and Windows 11?

Now you know how to dual boot Windows 11 with Windows 10. Before you close this page, please indulge our curiosity. Why did you want to learn how to do that? Why do you need both operating systems on the same PC? Let us know your reasons and whether everything worked well in the comments section below.