Differences among the methods of loading an extension in PHP

extension="ext.so"
zend_extension="/usr/lib/php4/ext.so"
zend_extension_ts="/usr/lib/php4/ext.so"

What are the differences?

From stackoverflow

• extension is used to load a user module that adds functionality into the language, such as database access, image manipulation. zend_extension and zend_extension_ts are used to load a module that extends the underlying PHP engine. One such example would be xdebug, an extension that allows you to debug your PHP applications. zend_extension_ts is for ZTS enabled PHP installations. To see if you have a ZTS build get the output from:

  <?php
  phpinfo();
  ?>