AHCI mode

AHCI mode was not enabled when I formatted and setup Windows on my latest system build. What is the performance advantage to having AHCI mode enabled on a system? Is there a way to enable it after setting up the system with it disabled?

 

According to the data, AHCI does provide increased performance of SATAII devices with "Native Command Queueing" NCQ in a multi-drive ( ala RAID ) scenarios. However, the only way to enable it for Windows, is before you install Windows. Since it represents a fundamental departure from the way the "bus" mechanics work, it is required to be enabled in the "BIOS/CMOS" and it also requires special motherboard drivers to be installed ( usually from floppy disk or slip-streamed Windows CD) at the time of the Windows install. If Windows is installed, before AHCI is enabled, there is currently no way to make Windows compatible.
Edit: if you own Vista there is a registry hack - see Microsoft's solution.

 

So, is it worth it to reformat/reinstall windows with AHCI mode enabled?

 

From a personal point of view, I wouldn't re-install Windows to get the AHCI. If you have Vista installed, then the registry tweak is the way to do it. If you don't own Vista, or if you don't run a web server, then the downsides of using AHCI, will outweigh any theoretical performance gains you might get. For instance, with AHCI, any of your SATA DVD/CD drives will not work at boot time. Only ATA/IDE optical drives will be recognized outside/ahead of Windows loading. The added overhead of drivers, and allocated ram, only begins to pay off when massive amounts of disk access are called for - often referred to as "command queueing". For desktop performance, I'd prefer to use a RAID 0 stripe set across two identical drives. This is tried and true technology that even old "Windows" gets along with. If you have a pair of 7200(or 10K) RPM SATAs hooked up in RAID 0, you'll have extraordinary performance without the requirement of "heavy system demands" to see that performance. With AHCI you'll barely notice anything at all - but with RAID 0 it's instant gratification. You will notice a performance boost - a big one. So, for me, re-loading Windows for RAID 0 = yes; for ACHI = no.