The Adaptec 78xx series is a legacy PCI SCSI card, and Adaptec has no official 64-bit drivers available through their product support. These drivers are incredibly hard to find in the x64 variety, and they also present an additional challenge to install on Windows 8.1 even if you can magically obtain them. Here’s the solution:
First download the unofficial Adaptec 78xx series x64 drivers.
NOTE: The 32-bit (x86) drivers for this legacy PCI SCSI card are difficult to find as well, so they are included in this bundle for convenience. Ignore them if they do not apply to you.
After you have downloaded the unofficial drivers, extract them to somewhere convenient (i.e. Documents or Desktop folder). The drivers have no installer, so we will need to go into Device Manager in order to manually install the drivers.
NOTE: If you’re trying to install these on Windows 8.1, there’s a big problem we need to resolve first. Windows 8.1 is particularly adamant about not allowing any drivers to be installed that haven’t received the Microsoft official stamp of approval. This isn’t such a bad idea, as maliciously hacked drivers can be very dangerous. Unfortunately, you run into cases like this where the vendor no longer supports their products and then when you try to install a 3rd party driver, Microsoft doesn’t want to let you. Here’s what we need to do:
In the charms menu, go to Settings, then Power. Hold down Shift on the keyboard and click “Reboot”. Choose “Troubleshoot”, “Advanced options”, “Startup Settings”, then “Restart”. Your computer will reboot, and present you with a menu letting you select various diagnostic options/modes. Pick “Disable Driver Signature Enforcement”. You will now boot into Windows in a special mode that will let us install our unofficial drivers. So far, so good.
Windows 8.0 / 8.1:
From the desktop, press Win+X on your keyboard and select Device Manager, or type “Device Manager” into the Windows 8.1 Search charm. This will bring you to a list of all the hardware in your computer.
Click on the Windows 7 Start button. Type the in “devmgmt.msc” into the search box and then hit the Enter key.
Now find the listing for an unknown SCSI storage device (it should have a yellow exclamation mark) and double-click it. Go to Drivers tab, then Update Drivers. Choose “Browse my computer for drivers software”, then Browse again. Locate the folder where you extracted the unofficial drivers and click Next. You will get a warning that the drivers are unsigned. This is normal. Choose to install them anyway. If you go to Device Manager after installation, you’ll notice that the SCSI adapter is now named Adaptec AIC-7870 PCI SCSI Controller (Emulated). This is perfectly normal.
And there you have it, a working AIC-7870 on Windows x64!!!