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

"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.

Press Win+R key to open the Run prompt.
Type in Regedit and press Enter to open Registry Editor.
Navigate to HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlset/Services/msahci
On the right hand side, right click on ""Start"" and then ""Modify"".
Input 0 in the ""Value data"" field (hexadecimal), the clik OK.
Close Registry Editor.
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.
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.
Press F10 to save the changes. Press Y if you're asked to confirm."

You can't switch modes between IDE and AHCI on a Windows system that already has the OS on it otherwise the HDD fails to boot and you get an error "INACCESSIBLE BOOT DEVICE"... at least in Windows 10. I found out the hard way when resetting the BIOS defaults and it wouldn't boot and had to re-install the entire OS to get it to work again, only to be told by a friend later that all I had to do was put the SATA mode back to IDE again :-/

However, the Windows 7 installation disks will only work if the target drive is in IDE mode. You would then need to coax the new Windows 7 installation to convert from IDE mode to AHCI mode but I just left my second laptop in IDE mode because I want to do a quad boot system that boots Windows 7 64-bit, Windows 7 32-bit, Windows 98SE, and MS-DOS 7.10 . TurboCAD 2017 does not work right in Windows 64-bit only works right 32-bit Windows. Likewise, I do not want to have to pay $5,000 for Maxisquash's er I mean Microsoft's latest Fortran compiler. I want Fortran aand PL/I compilers that I can afford.