I am sorry to hear you are having problems but let me help you.
The iaStor file comes preinstalled in the Operating System with the AHCI mode. Once the IRST driver is installed in the operating system the file/driver will be updated by the Intel® driver.
What I mean is that the driver is part of the OS and it cannot be uninstall from the system since it comes already preinstalled in the OS by MS.
Aha, now that makes sense with what I've been seeing. I couldn't find what installed because it was the OS that had installed it. Interesting. So, what does this thing do?
The IaStor.sys is a Windows driver. A driver is a small software program that allows your computer to communicate with hardware or connected devices. This means that a driver has direct access to the internals of the OS, hardware etc.