Newbie : Linux Word Size...

I'm running Linux (2.4.9) on an Intel box and trying to determine what is going on with this test :

Very simply, I have a function in C that goes as follows :

void f() {
  char buf[7];
}

When compiling to assembly via gcc -S and looking at the output, I see the function looks as follows :

f:
        pushl   %ebp
        movl    %esp, %ebp
        subl    $24, %esp
        leave
        ret

Why is the assembly subtracting 24 bytes for a 7 byte buffer?  I know it has to be word aligned, but when I change buf[7] -> buf[8] I get the expected results :

f:
        pushl   %ebp
        movl    %esp, %ebp
        subl    $8, %esp
        leave
        ret

Shouldn't buf[7] produce the same output?

Thanks,
Steve