InterBase is a popular database put out by Borland/Inprise. More information about InterBase is available at http://www.interbase.com/. Oh, by the way, InterBase just joined the open source movement!
To enable InterBase support configure PHP --with-interbase[=DIR], where DIR is the InterBase base install directory, which defaults to /usr/interbase.
Note to Win32 Users: In order to enable this module on a Windows environment, you must copy gds32.dll from the DLL folder of the PHP/Win32 binary package to the SYSTEM32 folder of your windows machine. (Ex: C:\WINNT\SYSTEM32 or C:\WINDOWS\SYSTEM32). In case you installed the InterBase database server on the same machine PHP is running on, you will have this DLL already. Therfore you don't need to copy gds32.dll from the DLL folder.
The behaviour of these functions is affected by settings in php.ini.
Table 1. InterBase configuration options
The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.