Why should I choose (or not) AHCI over IDE in my PC's BIOS settings?

AHCI vs IDE – Benchmark & Advantage

Excerpt: Advantage of AHCI

1. Hot-Plugging
2. Native Command Queuing (might improve computer/system/hard disk responsiveness, espcially in multi-tasking environment
   ...
   

Verdict:

These extensive benchmarks clearly show to us, AHCI (NCQ) definitely could improve computer system responsiveness, transfer rate, number of IO per second and the list goes on.

You can see AHCI as the language which the controller uses to speak with the system. The disk can't see if AHCI is being used or IDE emulation. If you use AHCI, all Serial ATA features are available, while you don't need any drivers specific to your controller.

To actually use AHCI, the OS (whether that's Windows, Linux or even Ghost) has to have an AHCI driver. Windows Vista and 7 include the driver, but don't install it if the boot drive's controller doesn't have AHCI enabled. Similarly, the IDE driver doesn't get installed if the IDE controller is disabled. That's why you can't just toggle the setting in the BIOS on an already installed Windows system.

Ghost 2003 was released in 2002, a few years before the AHCI specification was completed. It's hardly surprising that Ghost 2003 doesn't support AHCI. Apparently the latest enterprise version of Ghost can run in a boot environment based on either Windows or Linux, so it's likely that version does support AHCI.

Here in 2012, per this performance comparison, it doesn't seem to be urgent for a single user workstation. However, AHCI is a better and more modern option and you should always use it when you can.

From that article:

• If your application requires hot-plug drive support or redundant disks, then AHCI is the only choice.

• IDE mode can occasionally benefit from slightly faster read and write speeds in some tests.

• TRIM support works in both modes fine

• Overall, most SSD drives deliver better performance in AHCI mode, but it is not night and day.

How do you know you're using IDE or AHCI? Go to Device Manager and expand the hard drive controllers. If you see "AHCI" in there, you are using AHCI.

The good news is that you can switch from IDE mode to AHCI in Windows 7 or Vista without reinstalling or even opening your PC case. Here's the MSFT KB article on how to do so.

1. Press Win+R key to open the Run prompt.
2. Type in Regedit and press Enter to open Registry Editor.
3. Navigate to HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlset/Services/msahci
4. On the right hand side, right click on "Start" and then "Modify".
5. Input 0 in the "Value data" field (hexadecimal), the clik OK.
6. Close Registry Editor.
7. Restart the computer. Press and hold the Delete while the computer boots up to enter BIOS setup. Your computer might use a different key, like F2 or something else. Please refer to your computer manual.
8. In BIOS setup, select "Integrated Peripherals" and put the marker where it says "SATA RAID/AHCI Mode". Now use the + and - keys or Page Up and Page Down keys to change the value from "Disabled" to "AHCI". This refers to recent versions of Award BIOS system. Your BIOS settings might be different. Please refer to your computer manual.
9. Press F10 to save the changes. Press Y if you're asked to confirm.