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Failover A backup operation that automatically switches to a standby system (database, server or network), if the primary system fails or is temporarily shut down. Failover is an important fault tolerance function of PACS.

FDDI See Fibre Distributed Data Interface.

Fibre Distributed Data Interface (FDDI) A method used to send data over an optical fibre network. This type of network supports data transfer rates in the order of 200 Mbps. This is more efficient at transferring data across a network than Ethernet networks (as the header used is smaller), and therefore allows greater amounts of data to be sent in the packets. See Ethernet and Packet.

File Transfer Protocol (FTP) A protocol used to transfer files and software between two computer systems. In a PACS environment this is often used to transfer files from the HIS or the RIS to PACS and vice versa. See Transmission Control Protocol/Internet Protocol (TCP/IP).

Firmware This is software that has been recorded onto read-only memory (ROM), which is retained when the hardware is turned off. The software contained in the ROM is used to set the start conditions when the hardware is switched on.

Frame grabber A device that takes analogue video signal as input and converts it to a digital image file, using the synchronisation signals of the video to establish the beginning of each frame. With a large frame buffer it is possible to digitise the video in real-time.

FTP See File Transfer Protocol.