# Windows 10 - On EFI systems, Windows can only be installed to GP disks.



## sew333 (Oct 12, 2012)

Hello. So i have a question about disk format while installing Windows 10 from bootable pendrive. 
So 2 months ago i bought new SSD DISK Samsung 250 GB Evo . After plugging i run Windows 10 install from pendrive. Then of course i formatted disk without any warning and installed Windows 10 fine.
But........... 
Short time ago i decide to format disk again and install Windows 10 again from bootable usb. But this time during format i get message: "Windows 10 cannot be installed to this disk. The selected disk has an MBR partition table. On EFI systems, Windows can only be installed to GP disks." Of course i convert disk to GPT and Windows 10 installed fine. 
But why i get that message on second format when on first format not? 
I dont change anything in BIOS despite of devices booting. 


My disk is Samsung Evo 250 GB SSD , Asus Sabertooth Z97 Mark 2


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## Masterchiefxx17 (Feb 27, 2010)

Was Windows 7 or 8 previously installed?

It may have been that you had MBR selected as the format type.


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## sew333 (Oct 12, 2012)

No at first install i install fresh WIndows 10 Pro. Not upgrade. Then of course i formatted disk without any warning and installed Windows 10 fine. Short time ago i decide to format disk again and install Windows 10 again from bootable usb. But this time during format i get message: "Windows 10 cannot be installed to this disk. The selected disk has an MBR partition table. On EFI systems, Windows can only be installed to GP disks." Of course i convert disk to GPT and Windows 10 installed fine.
But why i get that message on second format when on first format not? 
On both times i choose the same UEFI KINGSTON USB.


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## Stancestans (Apr 26, 2009)

There's no way the first installation was an UEFI setup. That wouldn't work with an MBR disk and there's no way the disk changed from GPT to MBR without deleting all partitions.


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## sew333 (Oct 12, 2012)

So how is this possible then on my first install ( first format on my new ssd ) i installed to MBR partition at default. I choose bootable UEFI KINGSTON USB in UEFI. At second format it give me msg:""Windows 10 cannot be installed to this disk. The selected disk has an MBR partition table. On EFI systems, Windows can only be installed to GP disks."" LOL i cant understand this  On second format i choose the same UEFI KINGSTON USB in UEFI. I dont change anything in bios despite of booting.


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## Stancestans (Apr 26, 2009)

sew333 said:


> So how is this possible then on my first install ( first format on my new ssd ) i installed to MBR partition at default. I choose bootable UEFI KINGSTON USB in UEFI. At second format it give me msg:""Windows 10 cannot be installed to this disk. The selected disk has an MBR partition table. On EFI systems, Windows can only be installed to GP disks."" LOL i cant understand this  On second format i choose the same UEFI KINGSTON USB in UEFI. I dont change anything in bios despite of booting.


Rest assured that the first installation did not run in UEFI. Legacy boot (CSM) was/is enabled in BIOS, and Windows setup loaded in that mode, regardless of what you selected or think you selected.


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## sew333 (Oct 12, 2012)

Ah ok then. It was legacy then not doubt. But now i have 2 boot options with my ssd: SSD SAMSUNG 250 GB and Boot Manager SSD SAMSUNG 250 GB. 
Which from they are with GPT, boot manager?


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## Stancestans (Apr 26, 2009)

sew333 said:


> Ah ok then. It was legacy then not doubt. But now i have 2 boot options with my ssd: SSD SAMSUNG 250 GB and Boot Manager SSD SAMSUNG 250 GB.
> Which from they are with GPT, boot manager?


I believe that query has been responded to in your other thread. Read that article I linked to get you started on the boot process as handled by UEFI and BIOS firmware, then you can look deeper into UEFI if you are so interested in it.


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## sew333 (Oct 12, 2012)

One more thing. After i when i bought my disk i plug him of course.
After when i plug him i choose in bios boot from my : "UEFI USB KINGSTON" to install Windows 10. During install i formatted disk without  any warning and message, and installed Windows 10 fine. Question is. So first time it was have MBR or GPT? I dont had warning about GP partition. I just formatted without any warning and message.


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## Stancestans (Apr 26, 2009)

sew333 said:


> One more thing. After i when i bought my disk i plug him of course.
> After when i plug him i choose in bios boot from my : "UEFI USB KINGSTON" to install Windows 10. During install i formatted disk without any warning and message, and installed Windows 10 fine. Question is. So first time it was have MBR or GPT? I dont had warning about GP partition. I just formatted without any warning and message.


First time it was partitioned in MBR (by Windows setup running in legacy mode), that's why the second setup (in UEFI mode) threw that error. UEFI requires a GPT disk and won't have it any other way.


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## sew333 (Oct 12, 2012)

My mobo is with UEFI firmware. I read that MBR can be conflicting with UEFI on my mobo. Is that true? I had automatic repair during 1 boot of Windows 10. At second boot after restart it booted fine. Something like bios issue.


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## _nobody_ (Jan 1, 2016)

sew333 said:


> My mobo is with UEFI firmware. I read that MBR can be conflicting with UEFI on my mobo. Is that true? I had automatic repair during 1 boot of Windows 10. At second boot after restart it booted fine. Something like bios issue.


OK. :whistling:

Did not want to interfere in/with this discussion. But finally, I decided to jump in. 

SEW,

Please, read this very carefully. I am not ping-pong person, but about this... I guess, I am true professional (BIOS/boot-loaders wise).

So, let me spell out for you (and for others, who like to know more) couple of rules here.

Boot/BSP (Boot Support Package). It is BIOS dependant, In modern BIOSes (which are EFI 2.3+ compliant) you have all of 'em set to be UEFI OS compliant (almost always 64 bit, since the rule of thumb is: all 64 bit BIOSes are UEFI compliant BIOSes, but there are 32 bit UEFI instances as well). 

UEFI compliant OSes: All WIN 8+, all Linuxes distros (last 4 years)... U name them!
Legacy OSes: WIN7 and derivatives, WIN XP, WIN Vista and as such. :whistling:

*[1] LEGACY:* Once you installed legacy mechanisms the following happened. Ur BIOS does boot to something called Master Boot Record (MBR) on Ur HDD/SSD (very first 512B sector - Cylinder 0, track 0, sector 0).

For this to happen, you must have your UEFI BIOS set (in CMOS options), GFX to be set as legacy mode (vBIOS option), with something called Compatibility Support Mode (CSM) mode ON. Then, while you are installing your OS, BIOS will create MBR on your HDD, and you can then bring all OSes (even UEFI compliant) in this mode.

*[2] UEFI:* (MOST desirable for WIN10, if you ask me, the ONLY viable option): U must set CSM mode OFF, and better to set your GFX to NON legacy mode (UEFI mode), if such option exists!

Then, you'll have the following: your UEFI compatible BIOS will understand logical geometry of your HDD/SSD, and will create boot directory, from where you can boot your WIN10 bootloader.
_______

Usually, you will be NOT able to enter 2.3.1 (latest 2.40) EFI BIOS shell (forbidden by BIOS vendors), but if you are proficient enought, you can hack into it (I always do hacking to understand, what is under the hood)! :grin:

_nobody_


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## Stancestans (Apr 26, 2009)

sew333 said:


> My mobo is with UEFI firmware. I read that MBR can be conflicting with UEFI on my mobo. Is that true? I had automatic repair during 1 boot of Windows 10. At second boot after restart it booted fine. Something like bios issue.


Not at all. UEFI firmware can emulate BIOS functionality (CSM/Legacy) and work with MBR disks just fine. However, you should be consistent with whether you want to use UEFI or legacy. Mixing them is not a good idea, so if you decide to use legacy mode + MBR you will encounter boot problems if you later switch to UEFI (without legacy support).


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## sew333 (Oct 12, 2012)

I had only 2 boot options in UEFI to choose1 SSD SAMSUNG 250 GB ( MBR )and UEFI KINGSTON USB. And after i chang boot from UEFI KINGSTON USB to P1 SSD SAMSUNG 250 GB automatic repair happens only at 1 boot of Windows 10. Then after i click restart from automatic repair screen i was boot to Windows 10 fine. So can you explain me why? Is this because UEFI conflict with MBR? Or that doesnt matter?

It looked like this:


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## Stancestans (Apr 26, 2009)

sew333 said:


> I had only 2 boot options in UEFI to choose1 SSD SAMSUNG 250 GB ( MBR )and UEFI KINGSTON USB. And after i chang boot from UEFI KINGSTON USB to P1 SSD SAMSUNG 250 GB automatic repair happens only at 1 boot of Windows 10. Then after i click restart from automatic repair screen i was boot to Windows 10 fine. So can you explain me why? Is this because UEFI conflict with MBR? Or that doesnt matter?
> 
> It looked like this:


UEFI bootloaders register themselves with UEFI firmware (this info is stored in a configurable boot manager). When you had the thumb drive as the first UEFI boot device, the UEFI bootloader on it must have been registered in the default UEFI boot manager of the firmware. When you changed the boot device to the ssd, startup repair ran to register the bootloader on the ssd with the default boot manager of the firmware. UEFI implementation is not the same in all systems.

I am not an expert in UEFI or system firmware and I don't intend to be one. I only learn what I need to know in order to work with it AS IS. If you wanna play with different firmware configurations and how they work with operating systems and handle boot processes, that's your business. I linked an introductory article that should get you started with your quest to know more, plus you can look up UEFI, GPT, BIOS, MBR, CSM, bootloaders, boot managers and all of that stuff if you want. Educating you on these subjects is not the intended purpose of TSF. If in the course of seeking help you pick up something new, well and good, but teaching you these stuff is not our prerogative. I believe your original problem has been addressed and there's no reason why this matter should be discussed any further. Your system is running fine, but you seem hell bent on trying to prove that UEFI works the way it isn't designed to. That should be a subject of debate elsewhere, not on this (sub)forum.


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## sew333 (Oct 12, 2012)

Stancestans said:


> Not at all. UEFI firmware can emulate BIOS functionality (CSM/Legacy) and work with MBR disks just fine. However, you should be consistent with whether you want to use UEFI or legacy. Mixing them is not a good idea, so if you decide to use legacy mode + MBR you will encounter boot problems if you later switch to UEFI (without legacy support).


But for some reason Windows 10 was starting Automatic Repair during 1 boot. When i click restart on Automatic Repair screen , then Windows booted fine in second time. So there must be some reason. Maybe because partiion was on MBR? Or this is not reason?

You said:"UEFI firmware can emulate BIOS functionality (CSM/Legacy) and work with MBR disks just fine."

Also somebody said to me this:"UEFI booting requires a GPT disk. This is why Windows has to fix itself and only boots in 2nd cycle - as you keep trying to boot UEFI to an MBR disk." 



What you think?


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## Stancestans (Apr 26, 2009)

sew333 said:


> But for some reason Windows 10 was starting Automatic Repair during 1 boot. When i click restart on Automatic Repair screen , then Windows booted fine in second time. So there must be some reason. Maybe because partiion was on MBR? Or this is not reason?
> 
> You said:"UEFI firmware can emulate BIOS functionality (CSM/Legacy) and work with MBR disks just fine."


The first installation of Windows 10 was run in legacy mode, and Windows setup partitioned your drive in MBR style. Your UEFI firmware handled booting from an MBR disk just fine, because it had CSM/legacy support enabled. This CSM enabled your firmware to behave like a legacy BIOS firmware to boot your system from an MBR disk. Your UEFI firmware thus emulated the old/legacy BIOS funtionality.


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## sew333 (Oct 12, 2012)

Stancestans said:


> The first installation of Windows 10 was run in legacy mode, and Windows setup partitioned your drive in MBR style. Your UEFI firmware handled booting from an MBR disk just fine, because it had CSM/legacy support enabled. This CSM enabled your firmware to behave like a legacy BIOS firmware to boot your system from an MBR disk. Your UEFI firmware thus emulated the old/legacy BIOS funtionality.


Ok ok i understand. After i change boot priority from UEFI USB KINGSTON to P1 SAMSUNG EVO 250 GB, why it started booting first time with Automatic Repair and after restart ( 2 boot ) it booted fine. Is this related bios and that partitions that he was need 2 boots?
Somebody said to me this:"
"UEFI booting requires a GPT disk. This is why Windows has to fix itself and only boots in 2nd cycle - as you keep trying to boot UEFI to an MBR disk."


Can you explain me please? This is last question and this is very important.


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## Stancestans (Apr 26, 2009)

sew333 said:


> Ok ok i understand. After i change boot priority from UEFI USB KINGSTON to P1 SAMSUNG EVO 250 GB, why it started booting first time with Automatic Repair and after restart ( 2 boot ) it booted fine. Is this related bios and that partitions that he was need 2 boots?


It's related to how your UEFI firmware registers the boot device(s) in its default boot manager.



> Somebody said to me this:"
> "UEFI booting requires a GPT disk. This is why Windows has to fix itself and only boots in 2nd cycle - as you keep trying to boot UEFI to an MBR disk."
> 
> 
> Can you explain me please? This is last question and this is very important.


UEFI requires a GPT disk and UEFI compliant OS, but it will also boot from MBR disks if it has CSM enabled. If your UEFI system happens to NOT have CSM/legacy support, then a GPT disk is a must.


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## sew333 (Oct 12, 2012)

So why windows needed to fix itself and boots in 2nd cycle ( in 1 cycle Automati c Repair ) 

? It can be related to BOOT UEFI / PARTITION sheme? Or cause is elsewhere?


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## Stancestans (Apr 26, 2009)

sew333 said:


> So why windows needed to fix itself and boots in 2nd cycle ( in 1 cycle Automati c Repair )
> 
> ? It can be related to BOOT UEFI / PARTITION sheme? Or cause is elsewhere?


Because the boot device has changed and is different from what the UEFI default boot manager had in its configurable parameters. There have been cases of UEFI systems not booting after the USB drive that was used to install UEFI compliant OS is unplugged, even though the OS resided in a separate fixed hard drive. I'll say it for the last time, it's about the UEFI boot manager registering a default boot configuration, which includes the drives and bootloader(s) on them.

If the UEFI firmware fails to successfully initiate the boot process using its default boot manager's parameters and it reports that failure to the operating system's bootloader, it may trigger loading of the recovery environment in an attempt to correct the cause of the boot failure (startup repair). "Failure" in this case doesn't necessarily mean actual failure, but it can also mean inconsistency in what the UEFI boot manager has in its parameters compared to the current hardware environment. In other words, the recovery environment may load instead of the OS, in anticipation of boot failure, following the removal of boot media that was present when the UEFI boot manager was initially configured.

If after everything that I've said you somehow still don't get it, I advice you seek further enlightenment elsewhere. This is starting to feel like a dingy lecture room. I'm noticing a pattern of recurring questions, similar to some other member's whose thread was closed because of the same. I'm not sure if you are the same person as that member, but it doesn't really matter because I'll be requesting that this thread be closed if you do not cease asking the same thing over and over. I'm sure it's been mentioned among the forum rules which I'd like to believe you have read.


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## sew333 (Oct 12, 2012)

Ok thx for explanation. I will read this when i back from work. Anyway thank you for interest and help


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## sew333 (Oct 12, 2012)

Stancestans said:


> Because the boot device has changed and is different from what the UEFI default boot manager had in its configurable parameters. There have been cases of UEFI systems not booting after the USB drive that was used to install UEFI compliant OS is unplugged, even though the OS resided in a separate fixed hard drive. I'll say it for the last time, it's about the UEFI boot manager registering a default boot configuration, which includes the drives and bootloader(s) on them.
> 
> If the UEFI firmware fails to successfully initiate the boot process using its default boot manager's parameters and it reports that failure to the operating system's bootloader, it may trigger loading of the recovery environment in an attempt to correct the cause of the boot failure (startup repair). "Failure" in this case doesn't necessarily mean actual failure, but it can also mean inconsistency in what the UEFI boot manager has in its parameters compared to the current hardware environment. In other words, the recovery environment may load instead of the OS, in anticipation of boot failure, following the removal of boot media that was present when the UEFI boot manager was initially configured.
> 
> If after everything that I've said you somehow still don't get it, I advice you seek further enlightenment elsewhere. This is starting to feel like a dingy lecture room. I'm noticing a pattern of recurring questions, similar to some other member's whose thread was closed because of the same. I'm not sure if you are the same person as that member, but it doesn't really matter because I'll be requesting that this thread be closed if you do not cease asking the same thing over and over. I'm sure it's been mentioned among the forum rules which I'd like to believe you have read.


But this is not hardware failure/issue? You said:""Failure" in this case doesn't necessarily mean actual failure, but it can also mean inconsistency in what the UEFI boot manager has in its parameters compared to the current hardware environment."


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## Deejay100six (Nov 24, 2007)

Thread closed.


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