So, had to install XP beside Windows 7 64bit... Windows 7 64bit was installed while in BIOS hdd was set as AHCI...
To install XP, I've to put it to IDE. Now if I put AHCI i can boot in win7, but not in XP(BSOD), if I put IDE can't boot in win7(BSOD), can in XP.
Downloaded AHCI driver for my MB (MSI P55-GD55) and can't install them in XP, says no system requirements.
What to do? Is there a way to boot with IDE to windows 7 64bit without reinstall?
For XP the SATA/AHCI drivers must be installed during the OS installation.
You copy the drivers to a USB stick (or floppy disk) before you start the installation, and have them ready.
When you first boot the installation disk, during the first couple of windows that come up you will see a message appear at the bottom of the screen prompting you to press F6 to load drivers. Follow the instructions for "Loading SCSI Devices".
After loading the drivers you will proceed with the XP installation as usual.
Well, I didn't have drivers so I did install on IDE... And I don't want to do XP installation again, neither Windows 7 installation.
I want both OS to work without reinstall, or on IDE or on AHCI...
You want a lot!
Given your parameters that leaves you with only one option: change the Windows 7 installation to use IDE mode and remove the AHCI drivers.
I know how to change from IDE to AHCI:
AHCI : Enable in Windows 7 / Vista
But I have never wanted or needed to go the other way. You might try a web search to see if anyone else has done this.
Try this:
In the above Tutorial I linked you to, the procedure is to change the DWORD value from 3 to 0 to enable AHCI mode in Windows 7.
You would do the exact same procedure, but change the 0 to 3.
I can not guarantee this will work to run Windows 7 in IDE mode.
Quote