In computer science

Computer science

Computer science or computing science is the study of the theoretical foundations of information and computation and of practical techniques for their implementation and application in computer systems...

, the Server Application Programming Interface (SAPI) is the generic term used to designate direct module interfaces to web server

Web server

Web server can refer to either the hardware or the software that helps to deliver content that can be accessed through the Internet....

 applications

Application software

Application software, also known as an application or an "app", is computer software designed to help the user to perform specific tasks. Examples include enterprise software, accounting software, office suites, graphics software and media players. Many application programs deal principally with...

 such as the Apache HTTP Server

Apache HTTP Server

The Apache HTTP Server, commonly referred to as Apache , is web server software notable for playing a key role in the initial growth of the World Wide Web. In 2009 it became the first web server software to surpass the 100 million website milestone...

, Microsoft IIS, or iPlanet

IPlanet

iPlanet was a product brand that was used jointly by Sun Microsystems and Netscape Communications Corporation when delivering software and services as part of a non-exclusive cross marketing deal that was also known as "A Sun|Netscape Alliance"....

. Microsoft

Microsoft

Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...

 also uses the term in ISAPI

ISAPI

The Internet Server Application Programming Interface is an N-tier API of Internet Information Services , Microsoft's collection of Windows-based web server services...

 and the defunct Netscape used the term NSAPI

Netscape Server Application Programming Interface

The Netscape Server Application Programming Interface is an application programming interface for extending server software, typically web server software.-History:...

.

As an example, PHP has a direct module interface called a SAPI for different web servers. For PHP 5 and Apache 2.0 on Windows, it is in the form of a DLL

DLL

DLL may refer to:* Data link layer, a layer in the OSI network architecture model* Delay-locked loop, a device to reduce clock skew in digital circuits* Doubly linked list, a data structure in computer programming...

 file called php5apache2.dll. The DLL is a module that provides an interface between PHP and the web server, written in a form that the server understands. This form is what is known as a SAPI.

There are different kinds of SAPIs for different languages.
For example, the most common SAPIs for PHP

PHP

PHP is a general-purpose server-side scripting language originally designed for web development to produce dynamic web pages. For this purpose, PHP code is embedded into the HTML source document and interpreted by a web server with a PHP processor module, which generates the web page document...

language are PHP CLI and CGI.