Digital BW, The Print

In my quad2200 folder in the quadtone folder I have .quad paper
profiles/curves.  In my 2200-uc folder in the profiles folder I have
.qidf paper profiles/curves.  When I go into Curve Creation in QTR and
open a file it's a .qidf.  Sorry but what's the difference between
.qidf and .quad?  I have UC-EEnhMatte-cool.quad and
UC-EEnhMatte-cool.qidf but I only have UCmk-MBW-cool.quad and not
UCmk-MBW-cool.qidf.

Thanks,

Tom