  FireWire IEEE 1394/BWhat is the data transfer speed for FireWire?
What is the data transfer speed for FireWire? To understand this, first we must understand what it is and the different versions of FireWire available. FireWire, i.Link, and IEEE 1394 are similar. FireWire is the brand of IEEE 1394 made by Apple Inc. and i.Link is the Sony Corporations' brand of IEEE 1394 implementation. The IEEE 1394 standard, however, defines a backplane interface. FireWire is a PC, or personal computer, as well as digital audio and digital video serial bus interface standard. It offers high speed communications and isochronous real-time data services. In many applications, FireWire has replaced Parallel SCSI due to the lower implementation costs and the easier, more adaptable cabling system. The standard that has been adopted as the High Definition Audio-Video Network Alliance (HANA) standard connection interface for A/V component communication and control is IEEE 1394. FireWire is also available in fiber optic, wireless, and coaxial versions using the same isochronous protocols.
Since 1995, almost all modern digital camcorders have included a FireWire connection. Many computers that are intended for home, as well as computers for professional audio/video use have built-in FireWire ports, including all Apple computers, most Dell computers, and all Sony laptop computers that are currently produced. FireWire is also widely available on retail motherboards for the DIY PCs, alongside the USB port. FireWire was used with beginning models of Apple's iPod, but the later models eliminated FireWire support in favor of USB because of space constraints and for a wider compatibility.
The first version of FireWire available is called FireWire 400. This connector has 6 pins and can transfer data at 100, 200, or 400 megabits per second, although the the actual transfer rates are 98.304, 196.608, and 393.216 megabits per second, or 288, 24.576 and 49.152 megaBytes per second respectively. These various transfer modes are commonly called S100, S200, and S400. Although USB 2.0 can operate at 480 megabytes per second in theory, the tests indicate that this speed is not usually attained. This could possibly be caused by the client-server architecture of USB, in comparison to the peer-to-peer network operation of FireWire, and the support for the memory-mapped devices in FireWire, which allows high-level protocols to run without forcing numerous interrupts and buffer copy operations on host CPUs. 4.5 meters, or 15 feet. is the cable length limit although up to 16 cables can be daisy chained by using active repeaters, external hubs, or internal hubs that are commonly present in FireWire equipment. The S400 standard limits any maximum cable length configuration to 72 meters. The 6-pin connector is usually found on desktop computers, and can supply power to the connected device. Many laptops and small FireWire devices use a 4-pin version and don't have any power connectors, although this version is fully compatible with 6-pin interfaces. Some laptops utilize the 6-pin powered connector, like Apple's recent products. The 6-pin powered connector adds power output to support external devices. Usually a device can pull around 7 or 8 watts from the port, however the voltage may vary significantly from different devices. Voltage should nominally be about 25 Volts, between 24 and 30, and is specified as unregulated. The implementation on Apple laptops is generally related to battery power, and may be as low as 9V but is more likely around 12 Volts.
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