The file extension AMS identifies so-called Adobe Monitor Setup files. These are setup files customized for specific monitor models that contain color calibration information. Thus, often manufacturers of monitors have provided these files for their models.
These files are used to determine the color representation as well as the RGB / CMYK color space conversion to ensure the same color representation and processing on different monitor models.
AMS files have since been replaced by csf files, but can still be processed by Photoshop.