AHCI (Advanced Host Controller Interface) is present on newer Intel chipsets such as 975X (ICH7), P965 (ICH8), and P35 (ICH9). AHCI mode is enabled in the BIOS and 3 settings are commonly available: IDE, AHCI, and RAID. The last two (AHCI and RAID) require a driver floppy and the F6 method when installing Windows XP otherwise the hard disks won't be detected.
AHCI mode brings 3 main advantages:
Supports NCQ (Native Command Queuing) allowing SATA drives to accept more than one command at a time and dynamically reorder the commands for maximum efficiency.
Supports hot plugging of devices
Supports staggered spin ups of multiple hard drives at boot time
However, in the real world the performance difference isn't huge.
The problem is that if you installed Windows in IDE mode (i.e. you didn't use F6 and supply a driver disk), then simply changing the BIOS setting to AHCI mode and rebooting will cause Windows to fail and will require a repair install. Most people have been advising to reinstall Windows if you want AHCI enabled.
Here you will find the sollution :
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Do you experience:
Suddenly very slow computer
Constant high CPU utilization during file transfer
Lame hard disk performance
The stuttering DVD drive
Choppy DVD playback
Your drive is always in PIO mode and you can’t set it to UDMA mode
If you have one of these problems most probably your drive has switches from UDMA to PIO mode.
What does it mean?
DMA is an abbreviation for Direct Memory Access, an access method for external devices where the data transfer is not done by the central processor, but by a small special processor called DMA controller. It uses a procedure called cycle stealing, where the central processor memory access cycles are delayed for very short times to intersperse DMA controller memory access cycles. Some newer, faster DMA modes are called UDMA (Ultra DMA).
The alternative, slow and inefficient data transfer mode is called PIO, Programmed Input-Output, where the central processor transfers data byte for byte or word for word. This requires many processor commands for each data word and therefore causes a high and unwanted processor load.
Solution is here:
1) Download the file from here: http://winhlp.com/tools/resetdma.vbs
2) Despite any warnings click on the [Open] or [Execute] buttons as required to execute the file resetdma.vbs. If you fear to download the file, you can use the manual method instead (see link below). Or you could download, save, and inspect the program with an editor like the Windows Notepad. It is a script text file.
3) If the program found any ATA channel to reset, reboot your computer and test all drives.
4) If the problem is still not solved, set the offending channel to PIO manually, reboot your computer, set the channel back to DMA, and reboot again.
5) Please report your results here http://winhlp.com/node/97.
For more technical background or menual method visit this site: