Focus on platform support rather than what Zend Server is.
From the first sentence the focus is on platform support but there needs to be some opening explanation of what Zend Server is. For example, what kind of application server is it. Is it a general purpose code framework which can be installed across a wide range of platforms and for a number of different web servers. Is it specialized in any type of application: Websites / RT / Embedded / Security. Are there types of PHP programming for which it is not intended.