Class and object changes
Date/time support
Migrating from PHP 5.0.x to PHP 5.1.x
PHP Manual

## Extensions

- Extensions that are gone from the PHP core

- Class constants in new PHP 5.1.x extensions

## Extensions that are gone from the PHP core

One of the first things you're likely to notice when you download PHP 5.1.x is that several of the older extensions have disappeared. Those extensions that are still actively maintained are available in the PHP Extension Community Library (PECL), at » http://pecl.php.net/.

Removed extensions
Extension | Alternative/Status
--- | ---
ext/cpdf | pecl/pdflib
ext/dbx | pecl/dbx
ext/dio | pecl/dio
ext/fam | Not actively maintained
ext/ingres_ii | pecl/ingres
ext/ircg | Not actively maintained
ext/mcve | pecl/mcve
ext/mnogosearch | Not actively maintained
ext/oracle | ext/oci8 or ext/pdo_oci
ext/ovrimos | Not actively maintained
ext/pfpro | Not actively maintained
ext/w32api | » pecl/ffi
ext/yp | Not actively maintained
ext/activescript | » pecl/activescript

Modules in PECL that are not actively maintained (i.e. have not been supported for some time, have no active maintainer working on them currently, and do not have any PECL package releases), are still available in SVN at » http://svn.php.net/viewvc/pecl. However, unreleased PHP modules are by their nature unsupported, and your mileage may vary when attempting to install or use them.

## Class constants in new PHP 5.1.x extensions

The Zend Engine 2.1 API allows extension developers to declare class constants in object oriented extensions. New extensions written for PHP 5.1.x, including SPL, PDO, XMLReader and date, have their constants in the format `PDO::CLASS_CONSTANT` rather than in the C format `PDO_CLASS_CONSTANT` in order to minimise pollution of the global namespace in PHP.

Class and object changes
Date/time support
Migrating from PHP 5.0.x to PHP 5.1.x
PHP Manual