Regarding [david at davidfavor dot com 07-Feb-2012 02:07]; not true (at least for me, running PHP 5.3.9 on Windows 7):
My php.ini file (not containing "E"): variables_order = "GPCS"
<?php
var_dump($_ENV); // => array, empty
echo getenv('OS'); // => Windows_NT
?>
If $_ENV is empty because variables_order does not include it, it will be filled with values fetched by getenv().
For example, when calling getenv("REMOTE_ADDR"), $_ENV['REMOTE_ADDR'] will be defined as well (if such an environment variable exists).