 |
|
| |
|
||||
 FireWire (also known as i.Link or IEEE 1394) is a personal computer and digital video serial bus interface standard offering high-speed communications and isochronous real-time data services. FireWire can be considered a successor technology to the obsolescent SCSI Parallel Interface. Almost all modern digital camcorders have included this connection since 1995. All Macintosh computers currently produced have built-in FireWire ports, as do all Sony PCs and many PCs intended for home or professional audio/video use. FireWire is also used on the Apple iPod music player, permitting new tracks to be uploaded in a few seconds and also for the battery to be recharged concurrently with one cable.
Standards and versionsMissing image
Logo_firewire125.png Firewire color logo FireWire was developed primarily by Apple Computer, completing development in 1995. It is defined in IEEE standard 1394 which is currently a composite of three documents: the original IEEE Std. 1394-1995, the IEEE Std. 1394a-2000 amendment, and the IEEE Std. 1394b-2002 amendment. Sony's implementation of the system is known as i.Link, and uses only the four signal pins, discarding the two pins that provide power to the device in favor of a separate power connector on Sony's i.Link products. The system is commonly used for connection of data storage devices and digital video cameras, but is also popular in industrial systems for machine vision and professional audio systems. It is used instead of the more common USB due to its faster speed, higher power distribution capabilities, and because it does not need a computer host. It also has native support for isochronous data transport (data that must be delivered with deterministic latency, such as audio or video). However, the small royalty that Apple Computer and other patent holders have initially demanded from users of FireWire ($0.25 per end-user system) and the more expensive hardware needed to implement it ($1-$2) has prevented FireWire from displacing USB in low-end mass-market computer peripherals where cost of product is a major constraint.  FireWire can connect together up to 63 peripherals in an acyclic network structure (as opposed to SCSI's linear structure). It allows peer-to-peer device communication, such as communication between a scanner and a printer, to take place without using system memory or the CPU. FireWire also supports multiple hosts per bus, and IP networks can be formed through software between FireWire-linked computers. It is designed to support plug-and-play and hot swapping. Its six-wire cable is not only more convenient than SCSI cables but can supply up to 45 watts of power per port, allowing moderate-consumption devices to operate without a separate power cord. (Note that the Sony-inspired iLink usually deletes the power part of the cable/connector system and only uses a 4-pin connector.) FireWire 400 can transfer data between devices at 100, 200, or 400 Mbit/s data rates (actually 98.304, 196.608, or 393.216 Mbit/s, but commonly referred to as S100, S200, and S400). Cable length is limited to 4.5 metres but up to 16 cables can be daisy-chained yielding a total length of 72 meters under the specification. FireWire 800 (Apple's name for the 9-pin "S800 bilingual" version of the IEEE1394b standard) was introduced commercially by Apple in 2003, allows an increase to 786.432 Mbit/s with backwards compatibility to the slower rates and 6-pin connectors of FireWire 400. The full IEEE 1394b specification supports optical connections up to 100 metres in length and data rates all the way 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 (also referred to as beta mode). With this new technology, FireWire, which was arguably already slightly faster, is now substantially faster than USB 2.0. FireWire devices implement the ISO/IEC 13213 "configuration ROM" model for device configuration and identification, to provide plug-and-play capability. All FireWire devices are identified by an IEEE EUI-64 unique identifier (an extension of the 48-bit Ethernet MAC address format) in addition to well-known codes indicating the type of device and protocols it supports. Security issuesDevices on a FireWire bus can communicate by direct memory access, where a device can use hardware to map internal memory to FireWire's "Physical Memory Space". The SBP (serial bus protocol) used by FireWire disk drives use this capability to minimize interrupts and buffer copies. In SBP, the initiator (controlling device) sends a request by remotely writing a command into a specified area of the target's FireWire address space. This command usually includes buffer addresses in the intiator's FireWire "Physical Address Space", which the target is supposed to use for moving I/O data to and from the initiator. On many implementations (particularly those using the popular OHCI interface, which includes all PCs and Macs), the mapping between the FireWire "Physical Memory Space" and device physical memory is done in hardware, without operating-system intervention. While this enables extremely high-speed and low-latency communication between data sources and sinks without unnecessary copying (such as between a video camera and a software video recording application, or between a disk drive and the application buffers), this can also be a security risk if untrustworthy devices are attached to the bus. For this reason, high-security installations will typically either purchase newer generation machines that map a virtual memory space to the FireWire "Physical Memory Space" (such as a G5 Macintosh, or any Sun workstation), disable the OHCI hardware mapping between Firewire and device memory, physically disable the entire FireWire interface, or don't have FireWire at all. (This feature can also be used to debug a machine whose operating system has crashed, and in some systems for remote-console operations.) Hot swapping warningAlthough firewire can technically be hot-swapped without powering down equipment, there are reports of cameras being damaged if the pins are accidentally shorted while swapping. Also, the potential difference between a computer and a camera (see Electrical potential) sometimes results in arcing (sparks) when plugging the camera in. This can in turn "fry" the sensitive firewire chip set of the camera, rendering the firewire port unusable. To ensure maximum protection of a consumer DV camera, both the camera and computer should be powered off before connecting a firewire cable. Most commercial grade equipment is less sensitive to being hot-plugged, although care should still be taken. History
1) When Apple was participating with the IEEE p1394 working group, they proposed licensing all of Apple's blocking patents for $3k, one time fee, and only for "the point of first use" ... the IC's that implement the protocols. Furthermore, there was a discount if a contribution was made to the IEEE undergraduate scholarship fund. Under that agreement, the IEEE agreed to include the appropriate patents in the standard. 2) The "Firewire" name was chosen by a bunch of engineers drinking too much beer after hours just before Comdex '93, when the project was about to go public (IBM, Apple, TI, WD, Maxtor, Seagate were all showing drives/silicon/systems). We were under the gun since the marketing droids would have picked some name like "Performa" if we hadn't acted soon. (The original project name, BTW, was "Chefcat" ... the name of my favorite coffee cup). FireWire won the "most signifcant new technology" award from Byte Magazine (RIP) at the show. 3) Apple never intended to charge for the use of the name "Firewire" ... you could get it for free if you just signed an agreement to use it *only* for a product that was compliant with IEEE 1394-1995 (the original version of the standard). 4) Steve Jobs was somehow convinced that Apple should change the game midstream and ask for $1 per port for the Apple patents (his argument was that it was consistent with the MPEG patent fees). 5) This annoyed everyone (including the original Apple FireWire staff) immensely ... particularly Intel which had sunk a *lot* of effort into 1394 (the improved 1394a-2000 standard is partly based on Intel work). The faction of Intel that doesn't like open standards like 1394 used this as an excuse to drop 1394 support and bring out USB 2 instead. (There are lots of other stories about this whole process, but this is the author's favorite). 6) Simultaneously, Sony and the other 1394 backers pushed *hard* back at Apple noting that they all had patents too .... and if Apple wanted $1 port, so did they ... which meant that Apple would have to pay about $15 to every else to do Firewire ... not a pleasant picture. The result was the "1394 Licensing Authority", which charges everyone $0.25 *per end user system* (like a car) that uses any 1394 technology. -- this section written by Michael Johas Teener, original chair and editor of the IEEE 1394 standards document, and technical lead for Apple's FireWire team from 1990 until 1996. See also
External links
ReferencesIEEE p1394 Working Group (1995). IEEE Std 1394-1995 High Performance Serial Bus. IEEE. 0-7381-1203-8. IEEE p1394a Working Group (2000). IEEE Std 1394a-2000 High Performance Serial Bus - Amendment 1. IEEE. ISBN 0-7381-1958-X. IEEE p1394b Working Group (2002). IEEE Std 1394b-2002 High Performance Serial Bus - Amendment 2. IEEE. ISBN 0-7381-3253-5. INCITS T10 Project 1467D (2004). Information technology — Serial Bus Protocol 3 (SBP-3). ANSI INCITS. ANSI INCITS 375-2004.
This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.
|
||
|
|
|
|
|
|
Copyright 2008 WordIQ.com - Privacy Policy
::
Terms of Use
:: Contact Us
:: About Us This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "ILink". |