机器位和php位之间的区别

I am using a Machine with processor Core i5 64 bit in Mac OSX Lion 10.7.5. But when I try to work with integer greater than 32 bit is not working as an integer.

INPUT

<?php 
var_dump(is_int( 4294967296 ));//2^32
var_dump(is_int( 2147483648 ));//2^31
var_dump(is_int( 2147483647 ));//2^31-1
?>

OUTPUT

bool(false)
bool(false)
bool(true)

But as my machine is 64bit so I should I not expect that 2^32 will work as an integer?

Is there any setting with PHP?

Or how can I know the machine bit structure using PHP?