Firewire Cable                Firewire 400(left)800 port(right)

Michael Marino

 What does this Firewire 800 do?

 Who or what groups invented it?when?

FireWire 800 was introduced commercially by Apple in 2003. This newer 1394 specification (1394b) and corresponding products allow a transfer rate of 786.432 Mbit/s with backwards compatibility to the slower rates and 6-pin connectors of FireWire 400. However, while the IEEE 1394a and IEEE 1394b standards are compatible, FireWire 800's connector is different from FireWire 400's connector, making the physical male and female (both 4 and 6pin) connectors and cables incompatible. An adapter is necessary to take advantage of the 800's backward compatibility.

The full IEEE 1394b specification supports optical connections up to 100 metres in length and data rates up to 3.2 Gbit/s. Standard category-5 unshielded twisted pair supports 100 metres at S100, and the new p1394c technology goes all the way to S800. The original 1394 and 1394a standards used data/strobe (D/S) encoding (called legacy mode) on the signal wires, while 1394b adds a data encoding scheme called 8B10B. With this new technology, FireWire, which was already slightly faster is now substantially faster than Hi-Speed USB.

 http://en.wikipedia.org/wiki/Firewire_800

Peter Simek

 What are some of the divices that connect with it?

In spite of a maximum rate of 400 Mbps for FireWire (S400) and up to 480 Mbps for USB 2.0, USB is trailing behind. Why? The performance disparity hinges on FireWire's application, which offers more robust data transfer overall compared to USB.

USB can only accomodate one external device per PC port, which is why high end PCs have as many as eight USB ports. While it is possible to use a USB hub in order for devices to share USB ports, the performance of this alternative varies widely.

Things are different with FireWire, with all the devices being connected in series forming a logical chain (peer to peer) and where the protocol also permits physical branchings. Thanks to this method, it is possible to span longer stretches. However, if an interconnected device needs to be removed, then it is necessary to interrupt the connection for all the devices that follow in the chain. There is, however, one aspect that FireWire cannot change, either - namely that the existing bandwidth must always be shared by all the devices.

Things are not going to stop at the available 400 Mbps. Accordingly, as far back as in May 2002, the IEEE standard 1394b was adopted, which envisages transfer rates of 800 and 1,600 Mbps (S800 and S1600). We tested the initial configuration.

 What are its uses?

The increased speed and supported category 5 (Cat 5) cable hop (cable connection distance between two devices) of FireWire 800 is due primarily to two improvements. A more efficient bus arbitration scheme, known as Bus Owner/Supervisor/Selector (BOSS) arbitration, reduces transmission overhead by allowing control information to be transmitted in parallel with data and by reducing collisions. A new data encoding scheme based on the IBM 8b/10b model increases transmission reliability by maintaining DC balance to reduce signal distortion, and improves error detection by simplifying control codes and limiting to 5 the number of consecutive zero-bits or one-bits.

FireWire 800 allows compliant devices to communicate over much longer Cat 5 connections. And because they are backward-compatible, FireWire 800 hubs make it possible to connect FireWire 400 devices up to 100 m apart. Neither the computer nor the remote devices need to support FireWire 800.

FireWire 800 includes specifications for using additional types of cable, including plastic and glass optical fiber. These newer cable technologies offer the potential for much longer hops when compliant devices become available.

 http://developer.apple.com/documentation/HardwareDrivers/Conceptual/HWTech_FireWire/Articles/FireW_concepts.html

 Evans Phiri

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