Win 11 Key Backward Compatible?

Leo625 · May 14, 2022

Hi All:
I am getting ready to put Win 11 on here so went to the store and bought 11 Pro. Now I learn it will only work with GPT. I can certainly make my system GPT but prefer not to. Can I use this key to install another Windows 10 Pro on this machine for dual boot?
Thanks for the advise.

Leo625

AddRAM · May 14, 2022

Not true, it can be installed on a MBR disk.
Lotsa tutorials here.
Not sure about the key, but someone will be along soon to answer that question.

hsehestedt · May 14, 2022

Windows 10 and 11 keys are interchangeable, so you can install 10 with it. As noted, you can use MBR fine with Win 11.

Out of curiosity, why the opposition to GPT? It's a superior scheme. :)

hsehestedt · May 14, 2022

One more note - someone correct me if I am wrong - but if you plan to dual boot, I don't think you even need a second key. Since it is the same machine, it should detect that Windows has been previously activated on that machine and activate automatically via a digital license. Have not tried that myself, but that is my guess as to what would happen. I'm sure that someone else will either confirm that or correct me if I am wrong.

jaree1961 · May 14, 2022

hsehestedt said:
One more note - someone correct me if I am wrong - but if you plan to dual boot, I don't think you even need a second key. Since it is the same machine, it should detect that Windows has been previously activated on that machine and activate automatically via a digital license. Have not tried that myself, but that is my guess as to what would happen. I'm sure that someone else will either confirm that or correct me if I am wrong.

@hsehestedt is correct. Tried it myself and YES it works flawlessly

Wynona · May 14, 2022

hsehestedt said:
One more note - someone correct me if I am wrong - but if you plan to dual boot, I don't think you even need a second key. Since it is the same machine, it should detect that Windows has been previously activated on that machine and activate automatically via a digital license. Have not tried that myself, but that is my guess as to what would happen. I'm sure that someone else will either confirm that or correct me if I am wrong.

I bought this machine with Windows 10 Pro, did a clean install of 10 Pro, then added Windows 11 Home (in error). Since my students all have Home anyway, I'll stick with Home for now. I didn't buy a copy of Windows 11.

spapakons · May 16, 2022

You can bypass compatibility check and install on MBR or even a very old system without UEFI (only Legacy BIOS), as long as it has a 64-bit CPU capable of running at least Windows 8 64-bit. No need to repeat anything here, just read the relevant threads at the Installation section. The official Microsoft ISO supports all versions, including Windows 11 Home and Pro. If you are asked for version, select Pro. You can use your key to activate. If you are not asked (because a Windows 8 key or later is detected in the UEFI Firmware and used automatically) and you get Windows 11 Home, you can then change the key to upgrade to Pro.

hsehestedt · May 16, 2022

spapakons said:
If you are asked for version, select Pro. You can use your key to activate. If you are not asked (because a Windows 8 key or later is detected in the UEFI Firmware and used automatically) and you get Windows 11 Home, you can then change the key to upgrade to Pro.

Just thought that I would add a related note here. If you are installing from a flash / thumb drive and you run into this situation that @spapakons notes above, where Windows setup does not ask what edition to install, simply do this:

Open notepad and type in these two lines:

[Channel]
Retail

Save the file as ei.cfg (make sure that there is no .txt extension at the end).
Drop that file into the \Sources folder of your Windows installation disk.

Windows setup will now offer you a choice of editions to install (Home, Pro, Education, etc.).

Of course, I'm making the assumption that you are using Windows media that includes all those editions, such as when you download an ISO image from Microsoft or you use the Windows Media Creation Tool.

cereberus · May 16, 2022

Trying to dual boot with mbr is really limiting if both OSs are on same drive. You can only have 4 primary partitions, so if on same drive, you would have the system partition, W11 partition, W10 partition, and that just leave 1 primary partition for general use.

It makes no sense to use legact mbt anymore.

Winuser · May 16, 2022

Leo625 said:
Hi All:
I am getting ready to put Win 11 on here so went to the store and bought 11 Pro. Now I learn it will only work with GPT. I can certainly make my system GPT but prefer not to. Can I use this key to install another Windows 10 Pro on this machine for dual boot?
Thanks for the advise.

Leo625

If your computer was already running Windows 10 Pro, you didn't need to buy Windows 11. You could have download an ISO from MS and upgraded to Windows 11 for free.

Bree · May 16, 2022

Leo625 said:
I am getting ready to put Win 11 on here so went to the store and bought 11 Pro. Now I learn it will only work with GPT. I can certainly make my system GPT but prefer not to. Can I use this key to install another Windows 10 Pro on this machine for dual boot?
Thanks for the advise.

Welcome to Eleven Forum Leo625

Microsoft's keys do not distinguish between Windows 10 or 11, all keys are now referred to by Microsoft as being for Windows 10/11. See for example the wording used in the Microsoft Store:

The same applies to the digtal licence. If your PC is already activated with a digital licence for Windows 10, then you can clean install the same edition of Windows 11 on it without providing a key and it will actvate from the existing digital licence for that PC. Alternatively you could upgrade you installed Windows 10 to Windows 11 for free.

The bottom line is that if you have an activated Windows 10 Pro on your PC now, then you can install Windows 11 Pro for free. You can save the key you bought and use it on a new build.

spapakons · May 17, 2022

cereberus said:
Trying to dual boot with mbr is really limiting if both OSs are on same drive. You can only have 4 primary partitions, so if on same drive, you would have the system partition, W11 partition, W10 partition, and that just leave 1 primary partition for general use.

It makes no sense to use legact mbt anymore.

If you dual boot, you need no more than 4 primary partitions. If you want to triple boot, you should use two or more disks. MBR is used to avoid wasting precious disk space for the extra partitions of GPT. Even better, you can create only a single NTFS partition taking the whole disk space and install Windows 11 without any hidden system partition. This in practice gives you a little more space than the 500MB of the hidden partition, since the data are aligned differently. When we are talking about small SSDs of 120GB or even smaller (tablets and old netbooks with only 32GB or 64GB space) any MB you save counts. Other than that I never noticed any gain in performance when using GPT to justify adopting it. Never seen any difference in compatibility either, assuming you have properly installed all drivers. There is nothing for me to justify using GPT instead of MBR, unless forced by the hardware (such as UEFI only system, Legacy not available, or using an NVMe SSD disk that can boot only in UEFI mode).

hsehestedt · May 17, 2022

This is not an attempt to discourage use of MBR, just some additional data points so that you have a more complee picture of the differences between MBR and GPT.

You may not notice any real differences in your daily usage, but there are technical aspects of GPT that make it greatly superior to MBR. Included among these:

Supports 128 partitions rather than 4 (technically, it's pretty much unlimited, the 128 partition limit is imposed by Windows, not GPT)
HDDs greater than 2TB are supported
Uses CRC for integrity checking
Contains backup copies of GPT partition and header info
Allows faster boot times

The CRC and backup copies allow for automatic repair of boot data. With MBR steps must be taken manually to attempt repairs.

While Win 11 can use MBR, this is technically unsupported.

NavyLCDR · May 17, 2022

spapakons said:
If you dual boot, you need no more than 4 primary partitions. If you want to triple boot, you should use two or more disks. MBR is used to avoid wasting precious disk space for the extra partitions of GPT. Even better, you can create only a single NTFS partition taking the whole disk space and install Windows 11 without any hidden system partition. This in practice gives you a little more space than the 500MB of the hidden partition, since the data are aligned differently. When we are talking about small SSDs of 120GB or even smaller (tablets and old netbooks with only 32GB or 64GB space) any MB you save counts. Other than that I never noticed any gain in performance when using GPT to justify adopting it. Never seen any difference in compatibility either, assuming you have properly installed all drivers. There is nothing for me to justify using GPT instead of MBR, unless forced by the hardware (such as UEFI only system, Legacy not available, or using an NVMe SSD disk that can boot only in UEFI mode).

So, I did an experiment. I created 2 Virtual Drives both 128 GB in size. The first was partitioned with MBR and 1 primary partition, marked as active. I applied a Windows 10 image to it. Then made it bootable with the BCDBOOT command for BIOS booting only.

The second was partitioned with GPT, 1 EFI system partition (100 MB), 1 MSR partition (16 MB), and the rest 1 primary partition. I applied the exact same Windows 10 image to it, and then made it bootable with the BCDBOOT command, system files saved to the EFI system partition, for UEFI booting only.

After all that, the OS partition on the GPT disk had 112.64 MB less free space than the OS partition on the MBR disk.

spapakons · May 17, 2022

You took into account only the OS partition. If you add the other small partitions, you lose over 1GB of space. I would use GPT only if the hardware forced me, as explained in my previous reply, or to create a single partition larger than 2TB on a hard disk larger than 2TB.

NavyLCDR · May 17, 2022

spapakons said:
You took into account only the OS partition. If you add the other small partitions, you lose over 1GB of space. I would use GPT only if the hardware forced me, as explained in my previous reply, or to create a single partition larger than 2TB on a hard disk larger than 2TB.

Nope. We will have to agree to disagree. Two exact same bootable installations of Windows 10, the loss due to GPT partitions is 112.64 MB, not 1 GB+.

hsehestedt · May 17, 2022

spapakons said:
You took into account only the OS partition. If you add the other small partitions, you lose over 1GB of space. I would use GPT only if the hardware forced me, as explained in my previous reply, or to create a single partition larger than 2TB on a hard disk larger than 2TB.

I'll let NavyLCDR respond, but I think he took the other partitions into account. He very clearly notes the MSR and EFI system partitions.

Again, not trying to push you to GPT, just want you to have accurate facts on hand so that your decisions can be based upon fact rather than fiction

.

cereberus · May 17, 2022

NavyLCDR said:
Nope. I'm afraid you are mistaken

Yep only difference really between an mbr install and an efi install is difference in size of mbr system partition and efi (50 MB as efi slightly larger by default) plus msr partition (16 MB) plus a slight difference in size of other two partitions.

So your 112 MB difference is about right, nothing like 1GB. If there is that much difference, I suspect reason is one install has a recovery partition, and other does not.

AddRAM · May 17, 2022

Most likely.

NavyLCDR · May 17, 2022

hsehestedt said:
I'll let NavyLCDR respond, but I think he took the other partitions into account. He very clearly notes the MSR and EFI system partitions.

Again, not trying to push you to GPT, just want you to have accurate facts on hand so that your decisions can be based upon fact rather than fiction :).

You are correct. I did take the other partitions into account. Here is Disk 4 and 5 (my experiment disks) in Minitool PW:

You lose 116 MB of disk space for the added partitions, but you gain a few MB of disk space back into the OS partition because the boot files (BCD) are in the EFI System Partition rather than in the OS partition itself.

Win 11 Key Backward Compatible?

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