Are you sure, that your SSD is running in AHCI Mode? To verify that you should check the name of the Intel Controller shown within the "IDE ATA/ATAPI Controllers" and - if applicable - the "Storage Controllers" sections of the Device Manager.
If your SSD is running in AHCI Mode, you can easily change the used driver by doing a right click onto the related AHCI Controller > "Update driver software > "Browse my Computer..." > "Let me pick ..." > let the Device Manager show all compatible devices > choose the device, which uses the driver named MSAHCI.SYS.
Well, the device manager does not show any IDE ATA/ATAPI Controller. It does show "Intel(R) ICH8R/ICH9R/ICH10R SATA RAID -controller" under Storage Controllers. The device driver on this storage controller is IastorV.sys.So even if I have no RAID config, I guess al my IO goes trough this driver.
The bios on this mobo is an intel RAID bios which includes AHCI, according tot community and according to the bios boot screen.
Maybe it is not possible to install mhahci on this config?
The fact, that you have no Intel SATA AHCI Controller, but an Intel SATA RAID Controller within your Device Manager, verifies, that the SATA Controllers have been set to "RAID Mode" within the mainboard BIOS. This doesn't make any sense, because you don't want to create any RAID array.
As long as you don't change the SATA Mode from "RAID" to "AHCI", you probably won't be able to use the generic MS AHCI driver named MSAHCI.SYS.
Enter the mainboard BIOS and look for an option to switch the Intel SATA Controllers from "RAID" to "AHCI".
I have exactly the same issue with the Dell BIOS in my Inspiron 545 – the only BIOS configuration options are “IDE” which doesn’t support AHCI or “RAID” which does apparently include AHCI support for single drives (so far as I can tell).
Dell’s documentation and support is abysmal, so I arrived at the same configuration as Slonk after much experimentation and repeated installs of Win7x64. With the Dell BIOS set to “RAID” and the IastorV.sys driver on a single X-25 160GB 34nm drive I get 10-15% better throughput than with the IDE BIOS mode and drivers.
I, too, wondered if this was the best configuration option within the annoying Dell BIOS limitations, though. I don’t have automatic TRIM in Win7, but at least the SSD performance is comparable to everyone else’s benchmarks for that drive and SSD Toolbox 1.1 appears to be able to issue TRIM commands via the IastorV.sys driver (again, so far as I can tell).
Any further thoughts?
As long as you are not able to set the Intel SATA Controllers to a clean "AHCI Mode" within the BIOS, you will not be able to get the automatic Trim support by using the generic MS AHCI driver.
Nevertheless you should think about replacing the old Win7 in-box Intel RAID/AHCI driver named IASTORV.SYS by an actual version of the Intel MSM or RST driver named IASTOR.SYS. This will have no negative effect on the use of the Optimizer of Intels Toolbox.