Memory footprint tests :
<?php
echo memory_get_usage()."\n"; // display 627760
$array = array_fill( 0, 2048, 'a' );
echo memory_get_usage()."\n"; // 824744, so 196984 for $array
unset( $array );
echo memory_get_usage()."\n"; // 627792
$spl=SplFixedArray::fromArray( array_fill( 0, 2048, 'a' ) );
echo memory_get_usage()."\n"; //644944, so just 17151 for $spl !!!
?>