ABOVE IS WRONG, See w8 (w7 example was wrong)http://support.microsoft.com/kb/2751461/en-us
This is due to changes in Windows 8 PnP in which Boot Start Drivers are not installed by default.
add to all lists. and ways.
1: do a system save restore point, with date in name. you will thank me later. grin.. and before flipping the registry setting to AHCI
I just did this to a w8 installed to SSD , on a M5a78Lmlx-plus mobo, with fresh bios flash. All other posts, everywhere show w7 solution for w8 and all failed to work, the above, works for w8 (MS KB)
the boot of w8 is 2x faster. in AHCI.
hope this helps others.