Why doesn't php exec() work on Windows?

Question

PHP

On a virtual machine under winXP, exec() and system() do not work, the script just hangs in the browser and nothing happens. Everything works fine without these commands.
safe_mode Off Off
Sample code;

<?php
exec('calc');
?>

What can prevent these operators from working on Windows?

Answer 1

The answer is this: in php.ini line
must be

allow_url_include = On

Answer 2

try double quotes
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