• Apache now uses an autoconf and libtool system for configuring the build processes. Using this system is similar to, but not the same as, using the APACI system in Apache 1.3.
• In addition to the usual selection of modules which you can choose to compile, Apache 2.0 has moved the main part of request processing into Multi-Processing Modules (MPMs).

• Many directives that were in the core server in Apache 1.3 are now in the MPMs. If you wish the behavior of the server to be as similar as possible to the behavior of Apache 1.3, you should select the prefork MPM. Other MPMs will have different directives to control process creation and request processing.
• The proxy module has been revamped to bring it up to HTTP/1.1. Among the important changes, proxy access control is now placed inside a Proxy block rather than a <Directory proxy:> block.
• The handling of PATH_INFO (trailing path information after the true filename) has changed for some modules. Modules that were previously implemented as a handler but are now implemented as a filter may no longer accept requests with PATH_INFO. Filters such as INCLUDES or PHP are implemented on top of the core handler, and therefore reject requests with PATH_INFO. You can use the AcceptPathInfo directive to force the core handler to accept requests with PATH_INFO and thereby restore the ability to use PATH_INFO in server-side includes.
• The CacheNegotiatedDocs directive now takes the argument on or off. Existing instances of CacheNegotiatedDocs should be replaced with CacheNegotiatedDocs on.
• The ErrorDocument directive no longer uses a quote at the beginning of the argument to indicate a text message. Instead, you should enclose the message in double quotes. For example, existing instances of ErrorDocument 403 "Some Message should be replaced with ErrorDocument 403 "Some Message" As long as the second argument is not a valid URL or pathname, it will be treated as a text message.
• The AccessConfig and ResourceConfig directives no longer exist. Existing instances of these directives can be replaced with the Include directive which has equivalent functionality. If you were making use of the default values of these directives without including them in the configuration files, you may need to add Include conf/access.conf and Include conf/srm.conf to your httpd.conf. In order to assure that Apache reads the configuration files in the same order as was implied by the older directives, the Include directives should be placed at the end of httpd.conf, with the one for srm.conf preceding the one for access.conf.
• The BindAddress and Port directives no longer exist. Equivalent functionality is provided with the more flexible Listen directive.
• Another use of the Port directive in Apache-1.3 was setting the port number to be used in self-referential URL's. The Apache-2.0 equivalent is the new ServerName syntax: it has been changed to allow specifying both the hostname and the port number for self-referential URL's in one directive.
• The ServerType directive no longer exists. The method used to serve requests is now determined by the selection of MPM. There is currently no MPM designed to be launched by inetd.
• The mod_log_agent and mod_log_referer modules which provided the AgentLog, RefererLog and RefererIgnore directives have been removed. Agent and referer logs are still available using the CustomLog directive of mod_log_config.
• The AddModule and ClearModuleList directives no longer exist. These directives were used to ensure that modules could be enabled in the correct order. The new Apache 2.0 API allows modules to explicitly specify their ordering, eliminating the need for these directives.
• The FancyIndexing directive has been removed. The same functionality is available through the FancyIndexing option to the IndexOptions directive.
• The MultiViews content-negotiation technique provided by mod_negotiation has become more strict in its default file matching. It will select only from negotiable files. The old behavior can be restored using the MultiviewsMatch directive.
• (since version 2.0.51)

  The functionality of the ErrorHeader directive was put together with the Header directive, since it was a misnomer. Use

  Header always set foo bar

  instead to get the desired behaviour.

• The module mod_auth_digest, which was experimental in Apache 1.3, is now a standard module.
• The mod_mmap_static module, which was experimental in Apache 1.3, has been replaced with mod_file_cache.
• The distribution has been completely reorganized so that it no longer contains an independent src directory. Instead, the sources are logically organized under the main distribution directory, and installations of the compiled server should be directed to a separate directory.

Extensive changes were made to the server API in Apache 2.0. Existing modules designed for the Apache 1.3 API will not work in Apache 2.0 without modification. Details are provided in the developer documentation.