http://php.net/archive/2015.php 

PHP 7.0.0 comes with a new version of the Zend Engine, numerous improvements and new features such as

• Improved performance: PHP 7 is up to twice as fast as PHP 5.6
• Significantly reduced memory usage
• Abstract Syntax Tree
• Consistent 64-bit support
• Improved Exception hierarchy
• Many fatal errors converted to Exceptions
• Secure random number generator
• Removed old and unsupported SAPIs and extensions
• The null coalescing operator (??)
• Return and Scalar Type Declarations
• Anonymous Classes
• Zero cost asserts