Most computer manufacturers now support a faster hard drive communication mode known as AHCI. You'll often see it as an option in your BIOS settings. The problem is, your Windows 7 computer won't boot if you just change the setting in the BIOS.
The reason is so simple. Windows 7 has a specific driver for an AHCI enabled BIOS. That driver is not activated by default if the BIOS setting was not enabled when Windows 7 was originally installed. Say what??
So this means you can switch an existing Windows 7 install from IDE mode to AHCI mode in the SATA configuration. You just have to do it in a specific order.
Download and install your manufacturer-specific AHCI drivers for Windows 7
Read this Microsoft KB article and run the Fix It For Me or make the appropriate registry change
Reboot your PC and go into BIOS setup. Switch the SATA controller mode to AHCI.
Reboot again and watch Windows 7 load just fine.
....and a whole lot faster.