Now most PCs now ship with Windows 7 installed on a drive thats in AHCI mode.
Usually because there can be some potential speed benefit.
But occasionally, an ignorant technician will install W7 with the drive set to IDE mode.
I recently needed to take an existing installation of Windows 7, and in an attempt to improve performance, I wanted to change the drive mode from IDE to AHCI.
I know W7 has native support for AHCI, but before jumping across, I decided to do some research first.
It turns out that W7 actually doesn’t automatically switch to AHCI mode once the hard drive has AHCI enabled in the BIOS.
The first step is to actually go into regedit, then look for:
HKLMsystemCurrentControlSetservicesMsahcistart
HKLMsystemCurrentControlSetservicesIastorvstart
Change the start value to: 0 (ie zero)
write down the original value… just in case.
Close regedit, then restart the PC.
While restarting, enter the PC BIOS, and change the HDD setting from IDE to AHCI
W7 will then start using the drive in AHCI mode.