title_body: SD Cards with Unusual File Types
upvoted_answer: This sounds like IMP format. The IMP file is a container for other directories files, namely (1) directories ending in .RES and (2) files ending in .FRK and .INF. From mobileread.com (no affiliation):
  
  
    IMP is an intermediate file format used to store eBook content for several eBook Readers, most notably the eBookwise-1150 and the REB 1200. These devices are end user names for products called the ETI-2 and ETI-1 respectively from http://ebooktechnologies.com/ (no longer available) The Wayback machine displays the last time this site was available Jun 20, 2010. Site downloads are still available from http://www.ebooksystem.net/support_download.htm
  
  
  You can find a list of compatible software here.