An S400 port, is another name for the IEEE 1394 interface port, better known in Apple products as a FireWire port and in Sony products as an i.Link port.
As with S400 ports, FireWire and i.Link ports are sometimes labelled with an "S" and then a number. This number indicates the megabits of information per second that the port can transfer.
S400 ports and cables are used for cables that transfer information between two computers or between a computer and another device. S400 ports can also provide power to the devices connected to them.
The IEEE-1394 interface system provides a relatively cheap, easy to use and flexible way of transferring data. It is also one of the fastest systems in consumer use.
S400 ports are used to connect your computer to peripheral devices such as printers and external hard drives. Because of S400 port's high data transmission speed, it is often used with multimedia devices such as digital cameras.
The most common devices that use S400 ports are Apple computers. The FireWire system is built into all Apple laptops and desktops, as well as most other Apple devices such as iPods. i.Link S400 ports may also be found on Sony digital cameras.