3tb drive works in win7, win 10 no.

You also have to enable AHCI drivers in Windows 7 first following the procedure you dug up. Doing it only for Windows 10 will break your Windows 7.

I would suggest that you do it first with Windows 7 following the procedure you dug up - well dug :) - in post #17. I would think that after that the AHCI drivers will automatically get installed in Windows 10 when you boot into it. ( It may not happen viceversa) If not you can do that exercise in post#20.

In anycase have a back up of Windows 7 and all your data in that drive before you meddle .

proof all options greyed out. begs the question, if you got this disk, you would be stuck to make it function just using win10 builtin gui tool. disk part might work. i right clicked the 3tb disc.

well dang it. win10 still cant deal with it greyed out options.

i booted win7 and erased partition. booted win 10, this is what i still see. right click greyed out, so i am stuck.
it is getting too hard.

I made it work using diskpart, me, not anyone else`s ideas.
some of you did not believe me either.
How to use diskpart to format a drive to GPT

Ok, still there is a MAJOR problem. After I made the disk work in win10, I booted win7.
Win7 can not see the disk in file manager.

Goto disk management, immediately message pops up saying disc 1 needs to setup as GPT.
So I did, then had to format disk.

SO I CAN NOT RUN WIN10, as it can not see the disk if win7 formats it, and win7 can not see the disk if win10 formats it. BUG in windows or is it a feature!

Does anyone have a solution? is this because of AHCI versus raid? I can imagine going to the trouble of switching and it still wont work. There is an incompatibility exposed here, does ANYONE believe me? IMO, this is a bug in windows 10, if it can not show a partition created in win7.

As pointed out, your MBR for both 7 and 10 are on Disk 2. This only happens when you have a dual boot setup on a single drive. The later OS, in this case windows 10 becomes the primary OS and therefore has the MBR. Yet you say it wasn't but the proof is in your attachment.

You can try using MiniTool Partiton Wizard and see if you can move the MBR to the C drive.

Plankton said:

As pointed out, your MBR for both 7 and 10 are on Disk 2. This only happens when you have a dual boot setup on a single drive. The later OS, in this case windows 10 becomes the primary OS and therefore has the MBR. Yet you say it wasn't but the proof is in your attachment.

You can try using MiniTool Partiton Wizard and see if you can move the MBR to the C drive.

I never had both drives connected when I installed either os. Each was unplugged so only one drive was in the system during the install. Each drive can boot independently. Right now I select which os to start by selecting which drive to boot from when powering on by hitting escape key which gives me the boot menu in the bios.

What do people mean by it shows in my pic? The win10 drive only shows a solid partition?? The win7 shows multiple partitions?
I first installed win7, afterwards win10 with the win7 drive disconnected.

I am going to try converting to AHCI. I have the AMD chipset drivers, the AHCI driver is in the AHCI folder and has a 64bit win7 listed. If I can get win7 booting AHCI then win10 looks easy.

IF I disconnect disc2 with win7, and boot win10 drive, and then show diskmanager, will this prove anything? From what your saying you think this will be impossible?

extremely easyto mod win7, i just did it switched to ahci.
How do I change HDDs from IDe to ACHI without reinstalling Windows 7 - [Solved] - Motherboards

on the reboot, win7 redetected the sata controller, now on ahci. next is win10
setting to zero forces a reload of the sata driver.

To resolve this issue, enable the AHCI driver in the registry before you change the SATA mode of the boot drive. To do this, follow these steps:

Exit all Windows-based programs.
Click Start, type regedit in the Start Search box, and then press ENTER.
If you receive the User Account Control dialog box, click Continue.
Locate and then click the following registry subkey:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Msahci
In the right pane, right-click Start in the Name column, and then click Modify.
In the Value data box, type 0, and then click OK.
On the File menu, click Exit to close Registry Editor.

You did a good work finding an easy method to change it to AHCI by just modifying the registry.

What do people mean by it shows in my pic?

Plankton said:

As pointed out, your MBR for both 7 and 10 are on Disk 2. This only happens when you have a dual boot setup on a single drive. The later OS, in this case windows 10 becomes the primary OS and therefore has the MBR. Yet you say it wasn't but the proof is in your attachment.

You can try using MiniTool Partiton Wizard and see if you can move the MBR to the C drive.

OK! here is proof. I pulled win7 drive out. i set bios back to raid. I booted win10.

notice diskmanagement only shows one solid win10 partiton.