uncached speed? important ?

I was at pc pitstop and everything was fine except got a yellow flad on my "Disk" Drive C and the problem was "uncached speed 4 MB/s (18%)" is this a big deal and if it does matter how would I go about improving it? Thank you.

   I did a search on "uncached spped" but saw nothing on how to improve if needed.

 

Pat..