Requirements

Currently, the minimum PHP version required for Zend Framework is PHP 5.1.4. The recommended version is 5.2.
These PHP extensions are included by default in most PHP installations and used by ZF components:

1. ctype
2. SPL
3. pcre
4. session
5. BCMath (optional, but strongly encouraged)

BCMath: Subtle differences in the results of native PHP functions and operators (e.g. math) may exist between platforms (e.g. 32 bit or 64 bit systems). Tiny math errors can arise when working with float data types. The ZF i18n components solve these problems by using PHP's BCMath extension, if present. Using a version of PHP with the BCMath extension enabled is highly recommended.

Severity	Issues affecting Zend Framework 0.2 with PHP 5.1.4, but resolved with PHP 5.2
	Arbitrary remote code execution possibility when using Zend_View. See PHP Security Blog and Hardened PHP Project

Table legend: Critical Major Minor