Low performance when creating arrays

Hello,
I don't know if this is a normal situtation or it is a bug or I'm
doing something wrong, but my application creates quite big arrays and
the php performance is quite low. Below I have made several tests,
which shows that creation time of multi-dimensional arrays is growing
rapidly. Is this a normal behaviour or maybe there is better solution
when making arrays. I use Windows XP, Apache, PHP 4.3.5. Thanks in
advance for any answer.

$test = Array();
$start = explode(" ", microtime());
for ($i = 0; $i < 100000; $i++) {
$test[] = "test";
}
$stop = explode(" ", microtime());
print ($stop[1]+$stop[0])-($start[1]+$start[0]);

-------Time: 0.24844598770142

$test = Array();
$start = explode(" ", microtime());
for ($i = 0; $i < 100000; $i++) {
$test[$i] = Array();
}
$stop = explode(" ", microtime());
print ($stop[1]+$stop[0])-($start[1]+$start[0]);

--------Time: 0.33644223213196


$test = Array();
$start = explode(" ", microtime());
for ($i = 0; $i < 100000; $i++) {
$test[$i] = Array(Array());
}
$stop = explode(" ", microtime());
print ($stop[1]+$stop[0])-($start[1]+$start[0]);

--------Time: 0.55727505683899


$test = Array();
$start = explode(" ", microtime());
for ($i = 0; $i < 100000; $i++) {
$test[$i] = Array(Array(), Array(), Array(), Array(Array()));
}
$stop = explode(" ", microtime());
print ($stop[1]+$stop[0])-($start[1]+$start[0])."<br/><br/>";

--------Time: 1.4375410079956