cd vs. chdir()

From a php file, is it not possible to change the working directory using a cd, or is it required to use the php function chdir()? Here is my test: <?php echo "test 1\n"; echo pwd; cd /var/log; echo pwd; echo "test 2\n"; system("pwd"); system("cd /var/log"); system("pwd"); echo "test 3\n"; echo getcwd()."\n"; chdir("/var/log"); echo getcwd()."\n"; system("pwd"); ?> and here is the output: test 1 /usr/hh/bin /usr/hh/bin test 2 /usr/hh/bin /usr/hh/bin test 3 /usr/hh/bin /var/log /var/log