it seems there's misinformation both in this thread & around the net.

iastorV is the AHCI driver with RAID capabilities, without the V you get AHCI but no RAID.

bill / intel are in cahoots to make our life difficult by rendering systems non-bootable if all this doesn't jive between bios/the current install. here's what you need to do - quoting someone from tomshardware - and can vouch, this works:

Go into the registry using regedit and change each of the "start" values in the registry keys below from 3 to 0 and this will allow you to change between the different modes by just changing the option in your bios each time you reboot.

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\pciide
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\msahci
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\iaStorV
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\iaStor