What do the "ATA/IDE Configuration" options in ASUS motherboard BIOS?
You can tell by looking in your OS' device list. If the device is attached to an IDE channel, it's not running in AHCI mode.
Enhanced/SATA allows you to map SATA devices to IDE, so operating systems without AHCI support can still make use of the disks. SATA+PATA usually means that SATA is mapped to primary IDE, while PATA is mapped to secondary IDE (in different possible combinations, eg. physical primary master/slave to logical secondary master/slave, or physical primary/secondary master to logical secondary master/slave).
- Choose Enhanced mode / PATA if you have an IDE device you'd like to support
- Choose Compatible mode if you have an IDE device and enhanced mode doesn't work with your OS
- Choose Enhanced mode with SATA if you have SATA devices that your OS can't find (plain SATA if you have no IDE devices attached, SATA+PATA if you have SATA and IDE)
- Choose Disabled if you have no IDE devices and SATA devices work properly in AHCI mode
It's also possible that the chipset on your board does not support AHCI, Intel is somewhat sadistic about that (they even have different revisions of the same chip, with the same name, with AHCI enabled and disabled!). And even if the chipset supports AHCI, the BIOS can disable it!
In either case, the SATA ports will always be provided with an "IDE" interface, and this configuration option above is only relevant in rare cornercases (very old operating system that supports only 4 IDE devices in total), where you have to "stuff together" IDE and SATA to let the OS access all devices through 2 IDE controllers ("primary" and "secondary").