Why does a PHP script constantly take up more memory?
<p>See this example:</p>

<pre><code>echo memory_get_usage() . "\n"; // 36640
$a = str_repeat("Hello", 4242);
echo memory_get_usage() . "\n"; // 57960
unset($a);
echo memory_get_usage() . "\n"; // 36744
</code></pre>

<p>Can anyone explain why after un-setting the variable the memory usage does not return to 36640</p>
