there is no any diffrence between static and non static 
global variable

static means fixed we should not change anything,but in non 
static we can change.

Static global has file scope and it can't be accessed 
outside of the file.
         while global has program scope and can be accessed 
outside of file in which it has been defined using extern 
keyword.

static global is fixed.but global variables are changed.

Chitra, "static global is fixed.but global variables are
changed." what does this mean?

Please do not answer like this if you are not sure.

What Rakesh said is true except that Static global
variable's scope is limited to its block.

Let us make it clear

int x=22;//global

int* function()
{
 static int x = 99; // static x in function
 return &x;
}

main()
{
 {
  //static x in block
  static int x = 88;
  
  //returns static in block
  printf("\nvalue: %d", x++);
 
  // static x in function
  int *p = function();
  printf("\nvalue from function: %d", *p);

  // change static x in function
  *p = 77;

  printf("\nvalue from function: %d", *p);
  // new value of static x declared in function
 }
 // returns global x
 printf("\nvalue: %d", x);
 
 //still static x declared in function is alive in memory
 //but cannot be accessed directly as X since the scope of 
 //x declared in function is limited to the boundary of 
 //the function
 printf("\nvalue from function: %d", *function());
}

a program can be spread across two or more files...
so, a global variable can be accessed by all the files..
where as, a static global variable can be accessed only by
the file in which it is declared...static means permanent
and hence the value in static global variable is shared by
all the  functions in that file...

what sandeep said is absolutely correct