Can PHP tell if the server os is 64-bit?

Note: This solution is a bit less convenient and slower than @Salman A's answer. I would advice you to use his solution and check for PHP_INT_SIZE == 8 to see if you're on a 64bit os.

If you just want to answer the 32bit/64bit question, a sneaky little function like this would do the trick (taking advantage of the intval function's way of handling ints based on 32/64 bit.)

<?phpfunction is_64bit(){    $int = "9223372036854775807";    $int = intval($int);    if ($int == 9223372036854775807) {        /* 64bit */        return true;    } elseif ($int == 2147483647) {        /* 32bit */        return false;    } else {        /* error */        return "error";    }}?>

You can see the code in action here: http://ideone.com/JWKIf

Note: If the OS is 64bit but running a 32 bit version of php, the function will return false (32 bit)...

To check the size of integer (4/8 bytes) you can use the PHP_INT_SIZE constant. If PHP_INT_SIZE===8 then you have a 64-bit version of PHP. PHP_INT_SIZE===4 implies that a 32-bit version of PHP is being used but it does not imply that the OS and/or Processor is 32-bit.

On Windows+IIS there is a $_SERVER["PROCESSOR_ARCHITECTURE"] variable that contains x86 when tested on my system (WinXP-32bit). I think it will contain x64 when running on a 64bit OS.

A slightly shorter and more robust way to get the number of bits.

    strlen(decbin(~0));

How this works:

The bitwise complement operator, the tilde, ~, flips every bit.

@see http://php.net/manual/en/language.operators.bitwise.php

Using this on 0 switches on every bit for an integer.

This gives you the largest number that your PHP install can handle.

Then using decbin() will give you a string representation of this number in its binary form

@see http://php.net/manual/en/function.decbin.php

and strlen will give you the count of bits.

Here is it in a usable function

function is64Bits() {    return strlen(decbin(~0)) == 64;}