Is Zend Optimizer available?

Yes, Zend Optimizer is installed on all SiteGround's servers.

More information about it can be found by using the phpinfo() function. To do this, you should create a simple php file (e.g. phpinfo.php) with the following line in it:

<?php phpinfo(); ?>

and upload it on your hosting account. Then you should open this file in a browser to see the full Apache/PHP information and the Zend Engine details can be found on that page. The path to the file should be:

http://yourdomainname.com/phpinfo.php