(TPF) A real-time mainframe operating system released by IBM around 1976. TPF is particularly suited to organisations dealing in very high I/O message switching and large global networks. Current users include British Airways (reservations), VISA International (authorisations), Holiday Inn, and Quantas. TPF was traditionally a 370/Assembler environment although the latest, release 4.1, contains C. Formerly known as ACP (Airline Control Program), it was renamed "TPF" to suggests its greater scope. It is common for TPF sites to use IBM's MVS and VM operating systems for off-line processing.