6.0, 7.0, CS, CS2
XMP sidecar files
XMP is short for Extensible Metadata Platform which is a metadata standard that Adobe built to house the information that relates to your picture files.
Information such as author, camera, resolution, color space and keywords are all stored in this format and for the most part the details are saved within the picture file itself, but when this is not possible the data is included in a separated sidecar file.
The presence of this information makes searching, sorting ...