Advanced Host Controller Interface (AHCI) is the native work mode for SATA drives. It's been in the Linux kernel since version 2.6.19. Enabling AHCI has two main benefits: support for hot pluggable SATA drives (just like USB) and Native Command Queuing (NCQ).
SATA drives are usually configured as legacy Parallel ATA by the BIOS and the OS. Follow these two steps to enable AHCI:
Add the AHCI module to the kernel image
We do this by editing /etc/mkinitcpio.conf and adding ahci to the MODULES array:
Then we rebuild the kernel image, so that it includes our module:
mkinitcpio -p kernel26
Configure from BIOS
This depends from one motherboard to another. Enter the BIOS and search for something like:
Enable SATA as: IDE/AHCI
SATA: PATA Emulation/Native/Enhanced
Choose AHCI or Native, save your settings and exit the BIOS. Consult your motherboard manual if you don't know which of the modes is AHCI since the naming can vary.