PowerNotebooks.com - Laptop & Notebook News & Articles
Links:Articles Home
Hard Drives Category Index
AHCI - What Is It Good For?
23 February, 2009 in Hard Drives
Almost anyone who has purchased a new notebook in the past couple of years without an operating system or with the intention of downgrading to Windows XP from Windows Vista has come across the Advanced Hardware Control Interface, or AHCI, and most of those who have encountered it have done so after banging their heads against the wall in frustration because Windows XP could not detect their hard drive.
AHCI is a new programming specification, introduced along with the Serial ATA (SATA) hard drive standard, and it is designed to allow computers to use the SATA standard's advanced capabilities, most importantly hot-plugging and native command queuing. AHCI is also not natively supported by Windows XP.
Hot-plugging is almost exactly what it sounds like - it allows a SATA drive (through an external SATA, or eSATA, connector) to be plugged and unplugged from a computer while the computer is running, much like current USB and IEEE 1394 Firewire external hard drives. eSATA has been slow making its way to laptops, but it is finally here, so this functionality has become more important than it was even a year ago.
Native Command Queuing is a technology designed to allow hard drives to intelligently optimize the order in which read and write commands are executed. In situations where multiple read/write requests are coming in at once (generally in a server environment, but it occasionally happens on any system), Native Command Queuing gives a slight increase to overall drive performance, as well as slightly decreasing hard drive wear. The benefit is small, but certainly present.
AHCI also eliminates master/slave handling, which old hands of the PC world may recognize from daisy-chaining IDE cables for multiple hard drives, and it adds support for 64-bit addressing, providing enhanced functionality within 64-bit operating systems.
On systems that use Intel Turbo Memory, AHCI is the key factor in showing Windows Vista or Windows 7 how to properly interface with the Turbo Memory module.
Ultimately, the feature of AHCI most visible (and, consequently, important) to most users is hot-plugging, as this adds in support for using an eSATA hard drive as a real external drive (e.g., removable at any time), and it also adds support for booting from these eSATA drives, which many more tech-savvy users will find a tremendous boon, as an external drive can be used for everything from testing new Linux distributions to dual-booting another version of Windows on a system with only one internal hard drive.
The catch of course is that Windows XP is not natively compatible with AHCI, and the easiest way to install XP on an AHCI-equipped machine is usually to simply disable AHCI in the BIOS. Without an eSATA port, very little is lost by doing this, but if you have a PC with an eSATA port, you may want to consider getting AHCI active. Unfortunately, if you simply turn on AHCI in the BIOS when it had been turned off, ANY operating system will stop booting. There are two main ways to enable AHCI: Preload special AHCI drivers onto your Windows XP disc through a process called "Slipstreaming," or load a special patch within XP itself after making a full backup of your data.
Preloading
To preload AHCI, you will need to slipstream the AHCI drivers into a burned copy of Windows.
Getting ready
1. Download and install nLITE from nLITE's download page.
2. Take your genuine Windows XP CD-ROM and copy the entire contents of the CD to a folder on your hard drive (for this example, we'll call the folder XP_source).
3. Download and extract the "32-Bit Floppy Configuration Utility" from Intel.
Sliptstreaming
1. Start nLite and point it toward your XP_source directory, then click "Next." You will go through several prompts before being given a choice of what you would like to actually do with nLITE.
2. Click the option to "Integrate Drivers."
3. Click on "Insert," then navigate to the folder where you extracted the Floppy Configuration Utility. Add BOTH INF files in this folder (IaAHCI.inf and IaStor.inf)
4. Click "Next" through the remaining options until you reach "Unattended Setup.
5. *OPTIONAL* Click on the "General" tab in unattended setup and type your Windows Product Key into the box so that you do not have to type the key in when installing XP
6. Click on "Next," then click "Yes" when prompted to start the process.
7. Click "Next" once this completes, then click "Make ISO" to create a bootable CD image that can be burned using an ISO-compatible burning program, such as Nero or the freeware IMGBurn. Be sure to save the ISO somewhere you can easily locate it.
With this method, you can now install Windows XP onto your AHCI-enabled computer with no trouble.
Patching
It is possible, of course, that you already have XP preinstalled with AHCI disabled. No need to worry - there is still a way to update to AHCI compatibility, although there is a risk of data loss, so pleasse be sure to make a system restore point and back up all of your important data before starting.
1. Download the Intel Matrix Storage Manager from Intel
2. Download each of the following files to your desktop:
ICH9M AHCI XP Patch
IaStor.sys
3. Copy IaStor.sys into your C:WindowsSystem32drivers folder.
4. Extract the ICH9M patch file to a folder on your desktop, then double-click the "IchXm_ahci_xp_drv_patch.reg" to add the entry to your registry.
5. Reboot your computer and go into your BIOS by using "F2" (or whatever the BIOS key is on your system)
6. Enable AHCI (navigate to the advanced page. Depending on your own BIOS, it may be on the Advanced page itself, or it may be in a subsection of the page. There will either be an option to "Configure SATA As" AHCI/IDE, or an option to select the installed OS. If the option is for the OS, set it to Windows Vista.
7. Press "F10" and choose to exit saving changes.
8. Allow Windows to boot
9. Windows will detect a new hard disk. Cancel the installation wizard and install the Intel Matrix Storage Manager you downloaded at the beginning of this process.
Using either of these methods should allow you to get AHCI running within Windows XP. Please note that we don't really advise enabling AHCI under Windows XP unless you are using an eSATA device, as the other benefits of AHCI are negligible enough to be safely considered not worth the trouble.