What is the difference between "File scope" and "program scope"

A variable declared globally is said to having program scope
A variable declared globally with static keyword is said to have file scope.

For example:

int x = 0;             // **program scope**   
static int y = 0;      // **file scope**  
static float z = 0.0;  // **file scope** 

int main()  
{  
   int i;   /* block scope */  
   /* .
      .
      .
   */ 
   return 0;  
}  

What is the difference between these two?