Thursday, 4 February 2010

Hot-Plug Hard Disks Like They’re USB Sticks with AHCI

Filed under: Hardware & Gadgets — Jan Goyvaerts @ 12:04

My upgrade to an SSD drive was going to require a reinstall of Windows anyway. I had to finally upgrade from XP to Windows 7 to get the TRIM support the SSD drive needs.

So while I was at it, I replaced my ASUS P5K motherboard with a Gigabyte EP45-UD3R. The difference between the two is that the Gigabyte has the ICH10R chipset from Intel which supports AHCI (Advanced Host Controller Interface). This allows SATA drives to run natively as SATA drives enabling features such as hot-swapping. The old 320 GB hard disk that I replaced with the SSD drive now serves as removable storage for backups. I simply slide it into a SATA drive cage for 3.5″ disks that I installed into my computer long ago. It only takes a few seconds for Windows to recognize it. When I’m done, I use the “safely remove hardware” icon in Windows to eject it like it was a USB drive. Then I take it out. (I don’t know why Microsoft chose the word “eject”. The disk doesn’t fly out of the cage.)

In the past I never used the drive cage much. Without AHCI you can’t plug or unplug hard disks without rebooting the PC. Now I use it all the time. It’s just as convenient as USB drives, except that internal drives are cheaper, and run at full speed. Modern hard disks are typically about twice as fast as the maximum speed supported by USB 2.0.

To use AHCI you need a motherboard that supports it and you need to enable AHCI in the BIOS before you install Windows. Though my Gigabyte motherboard supports AHCI on both its SATA controllers (one Intel and one Gigabyte), both were set to IDE mode by default. With the SATA controllers set to IDE you can use SATA hard disks, but you won’t get the all benefits that SATA provides. I suppose IDE mode is the default because Windows XP does not support AHCI unless you know how to inject drivers during the setup process.

Your operating system also needs to support AHCI. Windows XP needs drivers that can only be loaded during the setup process. Windows Vista and 7 have built-in drivers for AHCI.

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