Strcut padding?

[webinfinite@gmail.com]

#include <iostream>
#include <string>

using namespace std;

int main() {
char t1;
struct t2{
char x;
};

cout << sizeof(t1) << " " << sizeof(t2) << endl;

typedef char& x1;
struct x2{
x1 x;
};

cout << sizeof(x1) << " " << sizeof(x2) << endl;
}

output:
1 1
1 4

Can anybody tell me why the size of x2 is 4? Why it's not 1?