Lets compare the compilation time for all the four storage classes of variable in c.

L7Q6_External_Storage_Class_Compilation_Time.c

//External Storage Class Variable
//Speed Test
#include<stdio.h>
#include<time.h>
int i;
int main()
{
    for(i=1;i<=100000000;i++);

    int ticks=clock();
    printf("%f\n",(float)ticks/CLOCKS_PER_SEC);
    return 0;
}