The different kinds of FireWire® connectors can be identified by the number of pins that they have, though a few different physical shapes are used as well. Two of the common versions of the Institute of Electrical and Electronics Engineers (IEEE) 1394 standard are FireWire® 400 and 800. The numbers refer primarily to transfer speeds, but each standard also uses a different number of pins. FireWire® 800 also uses a connector type that is substantially different from the others, as it is more square in shape while the previous types were flat with a notch or a pointed end. Some FireWire® connectors use different configurations, though they are less common.
Each version of the FireWire® standard uses a unique number of pins, offers varying transfer speeds, and in some cases also makes use of connectors that are shaped differently. These different connectors are not always directly compatible with each other, due to the differing pin configurations, sizes, and physical shapes. All of the versions of the FireWire® standard are compatible though, which means it is possible to bridge different FireWire® connectors using a variety of adapters and cables.
When FireWire® was first introduced, the connectors used four pins. This version of the standard is referred to as FireWire® 400, and it uses the smallest connector out of all the different versions of the standard. A variation on this connector type uses six pins instead, though the additional connections only provide power to external devices, and do not offer additional transfer speed. Both four and six-pin FireWire® connectors are referred to as alpha connectors, and the six-pin version is substantially larger.
The third type of FireWire® connector is typically known as a beta connector. This connector uses nine pins and is physically larger than either the four or six-pin versions. Beta connectors are used with FireWire® 800 devices, though they are backward compatible with the correct adapters. When a FireWire® 800 device that is designed to use a beta connector is plugged into a FireWire® 400 device or port, performance and transfer speeds will typically suffer.
There are a few other types of FireWire® connectors, including proprietary connector types that use different versions of the IEEE 1394 standard. One example is IEEE 1394c, which is a variation of the specification that is designed to use a traditional Ethernet connector and twisted pair cable. This version of the standard allows one port to function as both an Ethernet connection and an IEEE 1394c connection at the same time.