The Telephony Application Programming Interface (TAPI) is a Microsoft Windows API, which provides computer telephony integration and enables PCs running Microsoft Windows to use telephone services. Different versions of TAPI are available on different versions of Windows. TAPI allows applications to control telephony functions between a computer and telephone network for data, fax, and voice calls. It includes basic functions, such as dialing, answering, and hanging up a call. It also supports supplementary functions, such as hold, transfer, conference, and call park found in PBX, ISDN, and other telephone systems. TAPI is used primarily to control either modems or, more recently, to control business telephone system (PBX) handsets. When controlling a PBX handset, the driver is provided by the manufacturer of the telephone system. Some manufacturers provide drivers that allow the control of multiple handsets. This is traditionally called "third-party control". Other manufacturers provide drivers that allow the control of a single handset. This is called "first-party control". Third-party drivers are designed to allow applications to see and/or control multiple extensions at the same time. Some telephone systems only permit one third-party connection at a time. First-party drivers are designed to allow applications to monitor and/or control one extension at a time. Telephone systems naturally permit many of these connections simultaneously. Modem connections are by nature first-party. TAPI can also be used to control voice-enabled telephony devices, including voice modems and dedicated hardware such as Dialogic cards. History TAPI was introduced in 1993 as the result of joint development by Microsoft and Intel. The first publicly available version of TAPI was version 1.3, which was released as a patch on top of Microsoft Windows 3.1. Version 1.3 drivers were 16-bit only. Version 1.3 is no longer supported, although some MSDN development library CDs still contain the files and patches. With Microsoft Windows 95, TAPI was integrated into the operating system. The first version on Windows 95 was TAPI 1.4. TAPI 1.4 had support for 32-bit applications. The TAPI standard supports both connections from individual computers and LAN connections serving any number of computers. TAPI 2.0 was introduced with Windows NT 4.0. Version 2.0 was the first version on the Windows NT platform. It made a significant step forward by supporting ACD and PBX-specific functionality. In 1997, Microsoft released TAPI version 2.1. This version of TAPI was available as a downloadable update and was the first version to be supported on