Installing Windows 11 in Legacy (MBR) Mode using DISM

Lex24

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I have successfully installed Windows 11 (v21996.1) on the new computer with SSD with MBR partition table. The installation was performed from the command line using install.wim file and dism command. The machine is new and supports both UEFI and Legacy boot, but I like to have each version of Windows installed on a single partition and also like the simplicity of the Legacy mode. Initially I tried to tweak the BIOS settings and then run the standard installation, but it always ended up in some "incompatibility" error. Using dism solves all those problems. Here is step-by-step summary.

1) Partition the drive with a third party tool. I use GParted, but any other modern partitioning utility should be ok.

2) Extract install.wim file from the ISO (it is located in \sources directory) and save it on a flash drive or on one of the logical partitions created in p.1) above.

3) Boot to Win 11 installation media and run the dism command, following the instructions starting from p. 2.1 here:


4) Make the OS partition active

diskpart
list disk
list vol
select disk x
select vol y
active
list vol

Active flag (*) will be shown in the left column.

5) Install the BCD (Boot Configuration Data) using bcdboot command (p. 2.9 at the link above):

G:\Windows\System32\bcdboot G:\Windows /s G:

Parameter /s might not be required on some systems (especially when installing the first instance of Windows) but it won't do any harm to use it all the time.

6) Update Master Boot Record and Partition Boot Sector

bootsect /nt60 G: /mbr

Replace drive letter G: as needed (it is the OS partition). If /mbr is skipped only Partition Boot Sector will get updated.


-------------
Hardware

ASUS UEFI/BIOS v311 x64
- Fast Boot - disabled
- Secure Boot - disabled (OS Type = Other OS)
- CSM - enabled
- Boot Device Control - Legacy OPROM only
- Boot from Storage Devices - Legacy only
- Boot from PCI-E/PCI Expansion Devices - Legacy only

500 GB M.2 NVMe SSD - 3 primary + 3 logical NTFS partitions
500 GB SATA3 HD - disabled from BIOS (3 primary + 2 logical NTFS partitions)

CPU - Intel Core i5-9400
Chipset - B360
 
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rpo

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I have successfully installed Windows 11 (v21996.1) on the new hardware with MBR partition table. The installation was performed from the command line using install.wim file and dism command. The machine is new and supports both UEFI and Legacy boot, but I like to have each version of Windows installed on a single partition and also like the simplicity of the Legacy mode. Initially I tried to tweak the BIOS settings and then run the standard installation, but it always ended up in some "incompatibility" error. Using dism solves all those problems. However, there is one issue which remains unresolved: MBR installed by Windows seems to be defective and a third party bootloader must be used to chainload the OS (see p.6 below for details). Here is step-by-step summary.

1) Partition the drive with a third party tool. I use GParted, but any other modern partitioning utility should be ok.

2) Extract install.wim file from the ISO (it is located in \sources directory) and save it on a flash drive or on one of the logical partitions created in p.1) above.

3) Boot to Win 11 installation media and run the dism command, following the instructions starting from p. 2.1 here:


4) Install the BCD (Boot Configuration Data) using bcdboot command (p. 2.9 at the link above).

5) Make the OS partition active

diskpart
list disk
list vol
select disk x
select vol y
active
list vol

Active flag (*) will be shown in the left column.

6) Workaround for Missing MBR

At this point the OS won't boot, at least on my system. A quick look at the hex dump in the Linux terminal shows that there is no MBR code written to the disk:

sudo hd -n 512 /dev/nvme0n1

Running the following command from Win 11 installation media will install MBR code but the OS still won't boot:

bootrec /fixmbr

The temporary workaround is to use another bootloader (Grub4Dos, Grub2, Syslinux) to chainload Windows 11. Here is an example of menu.lst in Grub4Dos which resolves the issue (assuming the OS is installed on the first partition of the first disk):

title Windows 11
chainloader (hd0,0)/bootmgr



-------------
Hardware

ASUS UEFI/BIOS v311 x64
- Fast Boot - disabled
- Secure Boot - disabled (OS Type = Other OS)
- CSM - enabled
- Boot Device Control - Legacy OPROM only
- Boot from Storage Devices - Legacy only
- Boot from PCI-E/PCI Expansion Devices - Legacy only

500 GB M.2 NVMe SSD - 3 primary + 3 logical NTFS partitions
500 GB SATA3 HD - disabled from BIOS (3 primary + 2 logical NTFS partitions)

CPU - Intel Core i5-9400
Chipset - B360
To fix Windows boot problem, create a Macrium Reflect rescue USB disk, boot from that disk and fix your issue.
 

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SIW2

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It installs fine using bios/mbr.

An alternative to the Apply method:

It skips the checks if these are added to boot.wim image 2 system hive

win11-labconfig.jpg


Code:
Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\whatever-you-named-the-loaded-system-hive\Setup\LabConfig]
"BypassTPMCheck" = dword: 00000001
"BypassSecureBootCheck" = dword: 00000001
 
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johnlgalt

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I'll be referring to this thread when I start bringing the older machines into the fold....
 

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Lex24

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@rpo

bootsect {/nt60|/nt52} {SYS|ALL|<DriveLetter>:} [/force] [/mbr]

Thanks, this is the solution I was looking for. I have edited my original post and added the following command:

bootsect /nt60 G: /mbr

I initially expected that running bcdboot command will also update Master Boot Record and Partition Boot Record as needed, but clearly this is not the case.
 
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TomJones

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Would it not be easier to use Winpass11 ? I've recently completed an upgrade to Windows 11 Insider Preview on an old AMD Phenom II based machine that uses MBR. The whole process to bypass the checks was quick and easy even if the actual upgrade was quire slow.
 

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Lex24

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Would it not be easier to use Winpass11?

1) The method described in the first post does not require any third party executables or scripts.

2) It offers the choice where to place the boot files. They can be placed on the same partition as all the remaining OS files, or on a separate partition:


# Boot and OS files are on a single partition "G"

bcdboot G:\Windows

# Boot files are on partition "F" and OS files are on partition "G"

bcdboot G:\Windows /s F:
 
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cereberus

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Frankly, it is not good practicd to install W11 as mbr in only one partition. UEFI is more secure, is not restricted to number of primary partitions. Legacy MBR that has the bcd files in same partition as the C drive was superseded by have a separate partition for the boot files way back in W7.

The only two reasons for have bcd files on same partition are

1) to save one primary partition - not an issue with UEFI

2) if you installed w10 on an external usb flash drive, you could only do it this way as historically W10 would only support 1 primary partition on (most) usb flash drives. However W10 has now supported multiple partitions on usb flash drives for several years, so even this restriction no longer applies.

There is no sound technical reason for using mbr in any form for W10/11 unless pc is only mbr compatible and most of these pcs are about a decade old and not really suitable for W11 anyway.
 

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Lex24

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Cereberus:

There is no sound technical reason for using MBR in any form for W10/11 ...

The primary reason I have decided to keep using MBR is partition "true hiding". The only boot managers that support "true hiding" I am aware of are Boot-US and Grub4Dos, and neither supports UEFI.

The currently booted instance of Windows will see "true hidden" partition (with another instance of Windows) as unknown file system, so there is no chance it will interfere with it (which could happen any time either by design or by accident if the partition is hidden the regular way or not hidden at all). For those familiar with MBR and PBR structure, hexadecimal notation, magic bytes and all that I'm providing a few links at the end of the post. From the perspective of the end user "true hiding" looks as follows.

Boot menu (system with 6 primary partitions on 2 disks):


After the boot-up GParted in Linux identifies true hidden partitions as "unknown file system":



Windows 10 installer gets fooled into thinking that true hidden partitions are filled up (while in fact they are both empty):


Windows 11 DiskPart can't see those partitions:



-----------------------
More information


Boot-US (commercial application):



Grub4Dos (open source, modern Chenall's versions)



Version 0.4.6a 2020-03-04 is considered stable:


Some code examples can be found in the last few posts here:


Adapting that code for "Grub4Dos for UEFI" should be possible, but dealing with multiple partitions assigned to each instance of Windows on UEFI system definitely makes the whole process of true hiding and unhiding much more complicated compared to MBR system with a single partition. In case anyone would like to try they could probably get some help here:

 
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jimbo45

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I have successfully installed Windows 11 (v21996.1) on the new computer with SSD with MBR partition table. The installation was performed from the command line using install.wim file and dism command. The machine is new and supports both UEFI and Legacy boot, but I like to have each version of Windows installed on a single partition and also like the simplicity of the Legacy mode. Initially I tried to tweak the BIOS settings and then run the standard installation, but it always ended up in some "incompatibility" error. Using dism solves all those problems. Here is step-by-step summary.

1) Partition the drive with a third party tool. I use GParted, but any other modern partitioning utility should be ok.

2) Extract install.wim file from the ISO (it is located in \sources directory) and save it on a flash drive or on one of the logical partitions created in p.1) above.

3) Boot to Win 11 installation media and run the dism command, following the instructions starting from p. 2.1 here:


4) Make the OS partition active

diskpart
list disk
list vol
select disk x
select vol y
active
list vol

Active flag (*) will be shown in the left column.

5) Install the BCD (Boot Configuration Data) using bcdboot command (p. 2.9 at the link above).

6) Update Master Boot Record and Partition Boot Record

bootsect /nt60 G: /mbr

Replace drive letter G: as needed (it is the OS partition).


-------------
Hardware

ASUS UEFI/BIOS v311 x64
- Fast Boot - disabled
- Secure Boot - disabled (OS Type = Other OS)
- CSM - enabled
- Boot Device Control - Legacy OPROM only
- Boot from Storage Devices - Legacy only
- Boot from PCI-E/PCI Expansion Devices - Legacy only

500 GB M.2 NVMe SSD - 3 primary + 3 logical NTFS partitions
500 GB SATA3 HD - disabled from BIOS (3 primary + 2 logical NTFS partitions)

CPU - Intel Core i5-9400
Chipset - B360
Hi there
Some isos now have install.esd instead of wim - presumably for space saving / booting problems on some machines from isos bigger than approx 4.7GB. So I'd modify your instructions to extract iso contents as before - then convert the eds to an install.wim.

However I think on an MBR type of machine you'll have a problem with booting an ISO if it spills over the 4.7 GB limit in any case.

As for MBR / vs GPT the main reason these days (although if your boot disk just contains only the OS might not be so relevant) is that MBR disks can only have 4 primary partitions (max) - and logical partitions of any sort are an absolute nightmare. GPT formatted disks don't have partition number limits. I believe though most MBR computers can access GPT disks - they just can't boot from them. You might also be lucky enough to have CSM on the older computer which allows GPT to boot on an MBR BIOS.

I think also some isos of W11 now don't have that particular parameter /mbr in the bootsect command - a possible get around if that's the case is to use the one from a W10 setup or possibly try the Macrium free stand alone recovery "Fix Windows boot problems" - but create the recovery using the PE option not the RE option in the popup.

Cheers
jimbo
 

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Lex24

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However I think on an MBR type of machine you'll have a problem with booting an ISO if it spills over the 4.7 GB limit in any case.

I am not aware of any such limitation. Please provide the link to the source of your information. Just to be sure, I have booted the following two ISOs using Ventoy USB flash drive (it is formatted in exFAT file system by default so the size limit of a single file is 16 EiB [Exbibyte]):

5.4 GiB - Win10_21H1_English_x64.iso

9.3 GiB - CentOS-Stream-8-x86_64-20210528-dvd1.iso

... MBR disks can only have 4 primary partitions (max) - and logical partitions of any sort are an absolute nightmare.
There is no nightmare. First you create one, two or three primary partitions, then one extended partition, and finally create logical partitions inside the extended one. There is no strict limit, it depends on the system, a hundred is easy on any XP era computer or newer.

I believe though most MBR computers can access GPT disks.
Hybrid MBR, tricky stuff, I have never tried it myself:


I think also some isos of W11 now don't have that particular parameter /mbr in the bootsect command - a possible get around if that's the case is to use the one from a W10 setup

Win11 Build 21996.1 has bootsect with /mbr. If some new build doesn't have it then just use the latest build that does.
 

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NavyLCDR

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On an old legacy BIOS system, GPT disks are accessed via a driver in Windows, not via a driver in BIOS. That's the difference.
 

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cereberus

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Per earlier posts that discuss logical partitions, on older MBR systems, rather than using logical partitions, I simply use virtual hard drives instead.
 

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  • Operating System
    Windows 10 Pro + others in VHDs
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    ASUS Vivobook 14
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    I7
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    Yep, Laptop has one.
    Memory
    16 GB
    Graphics Card(s)
    Integrated Intel Iris XE
    Sound Card
    Realtek built in
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    N/A
    Screen Resolution
    1920x1080
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    1 TB Optane NVME SSD, 1 TB NVME SSD
    PSU
    Yep, got one
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    Yep, got one
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    Stella Artois
    Keyboard
    Built in
    Mouse
    Bluetooth , wired
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    72 Mb/s :-(
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    Edge mostly
    Antivirus
    Defender
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