Does really SplFixedArray perform better than arrays?

Question

I\'m testing the SplFixedArray building an array with the days of the week, and I get the following results:

Answer 1

A SplFixedArray is supposed to be faster than arrays. It doesn't say anything about memory consumption (which is what you're testing here). From http://php.net/manual/en/class.splfixedarray.php:

"The main differences between a SplFixedArray and a normal PHP array is that the SplFixedArray is of fixed length and allows only integers within the range as indexes. The advantage is that it allows a faster array implementation"

However, using an array of 100000 entries, reveals that it also uses less RAM:

$users = array();
for ($i=0;$i<100000;$i++) { 
    $users[$i] = array('id' => rand(), 'name' => 'default');
}
echo memory_get_peak_usage(true); //returns 31457280

---

$users = new SplFixedArray(100000);
for ($i=0;$i<100000;$i++) { 
    $users[$i] = array('id' => rand(),
            'name' => 'default');
}
echo memory_get_peak_usage(true); //return 26738688