Pretty much all modern motherboards give the user the choice of ACHI or IDE mode for the SATA interface. For Windows XP, the IDE mode had the advantage of not requiring drivers to install, but at a cost of the features AHCI has to offer, such as NCQ and power management.
Native Command Queuing (NCQ) is generally used by traditional hard disks to allow them to plan how to carry out the read/write operations to minimise seek-times. As SSDs don’t have moving parts, some SSDs use NCQ to combining write operations together to improve write performance. AHCI also offers other features such as Hot-swap, port-multiplier and RAID.
So how much of a benefit does AHCI offer and is the extra over-head involved over IDE operations worth it? PC Perspective and Benchmark Reviews takes a look, with some in-depth tests on Benchmark Reviews:
Aside from inconsistencies in HDTune, when testing only single-threaded performance, IDE may perform marginally better than AHCI. The physical interface may be identical, but AHCI adds some additional instructions / overhead to the protocol, which slightly detract from the bandwidth available for data transfers. This slight performance hit is nullified by the performance gains seen when the attached device can utilize parallel IO (through the use of NCQ).
Source: PC Perspective
It’s quite interesting to see from the Benchmark Review’s results that depending on the benchmarks, some drives give better results with AHCI, while a few others do better with IDE. When it comes to performance, most users will probably not notice the difference apart from in benchmarks, but if one is using a laptop or is interested in AHCI specific features such as RAID, they will quickly notice if they’re not using the right mode.
Even though AHCI is the most logical mode to use in most situations, the IDE mode comes in very handy when it comes to running bootable tools such as BartPE or a bootable virus checker, since many bootable CDs can only access hard disks using the legacy IDE mode.