SD card & internal memory free space is not correct!

[Parham]

 Hi everybody!

 When I check setting->storage, calculated available space shown is much less than what I calculate the numbers shown for apps, Pictures, Videos, and Audio. Where is the missed Space?!!

[Thommo]

It is used for the operating system

[vghorbanian]

   Thx, but is there syetem files on  both Internal Memory and External Card? I thought that this issue is only for Internal Memory.