Unsetting array memory

gistfile1.php

<?php
$init = memory_get_usage();
$time = microtime();
echo "method 1 (unset): " . $init . "<br />";
$array = array();
for($i = 0; $i < 1000; $i += 1) {
  $array[] = 'string';
}
echo "after setup: " . memory_get_usage() . "<br />";
unset($array);
echo "diff: " . abs(memory_get_usage() - $init) . "<br />";
echo "time: " . abs(microtime() - $time) . "<br />";
echo "<br /><br />";


$init = memory_get_usage();
$time = microtime();
echo "method 2 (null): " . $init . "<br />";
$array = array();
for($i = 0; $i < 1000; $i += 1) {
	$array[] = 'string';
}
echo "after setup: " . memory_get_usage() . "<br />";
$array = null;
echo "diff: " . abs(memory_get_usage() - $init) . "<br />";
echo "time: " . abs(microtime() - $time) . "<br />";
echo "<br /><br />";


$init = memory_get_usage();
$time = microtime();
echo "method 3 (array_pop): " . $init . "<br />";
$array = array();
for($i = 0; $i < 1000; $i += 1) {
	$array[] = 'string';
}
echo "after setup: " . memory_get_usage() . "<br />";
for($i = 0; $i < count($array); $i += 1) {
	array_pop($array);
}
echo "diff: " . abs(memory_get_usage() - $init) . "<br />";
echo "time: " . abs(microtime() - $time) . "<br />";
echo "<br /><br />";


$init = memory_get_usage();
$time = microtime();
echo "method 3 (array_shift): " . $init . "<br />";
$array = array();
for($i = 0; $i < 1000; $i += 1) {
	$array[] = 'string';
}
echo "after setup: " . memory_get_usage() . "<br />";
for($i = 0; $i < count($array); $i += 1) {
	array_shift($array);
}
echo "diff: " . abs(memory_get_usage() - $init) . "<br />";
echo "time: " . abs(microtime() - $time) . "<br />";
echo "<br /><br />";


$init = memory_get_usage();
$time = microtime();
echo "method 5 (unset elem): " . $init . "<br />";
$array = array();
for($i = 0; $i < 1000; $i += 1) {
	$array[] = 'string';
}
echo "after setup: " . memory_get_usage() . "<br />";
for($i = 0; $i < count($array); $i += 1) {
	unset($array[$i]);
}
echo "diff: " . abs(memory_get_usage() - $init) . "<br />";
echo "time: " . abs(microtime() - $time) . "<br />";
echo "<br /><br />";
?>

method 1 (unset): 346476
after setup: 439000
diff: 268
time: 0.001166


method 2 (null): 346744
after setup: 438976
diff: 80
time: 0.000607


method 3 (array_pop): 346824
after setup: 438976
diff: 48152
time: 0.001316


method 3 (array_shift): 394976
after setup: 438976
diff: 0
time: 0.010679


method 5 (unset elem): 394976
after setup: 438976
diff: 0
time: 0.000982