Hopefully you installed Windows in AHCI mode, the default SATA mode setting in the BIOS. If you changed to IDE, you have some work to do, but I'll assume you are in AHCI mode.
Then again, are you checking the driver of the SATA controller, or the 840? You should be checking the driver of the SATA controller, which should be msahci with Windows 7, if the Intel driver was not installed. If you were checking the Disk/840's driver, and now check the SATA controllers driver, you may find you have the Intel driver installed. In Device Manager, find the SATA Controller, which is in the Storage Controllers entry, not in Disks.
Will you first confirm this for us? Given your comment about write speeds, I have a feeling the Intel driver is installed, and a quick fix for the lower write speeds can be done.