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Celebrating the independent kiwi spirit of invention.


FireWire, USB, and USB 2.0

By Ian Mander, 11 April 1999.

Question: Where do FireWire, USB 1.1, and USB 2.0 fit into things?

Answer: Both FireWire and USB 1.1 have advantages and disadvantages for different uses, but USB 2.0 (which at this stage is a proposal for a future standard) is another story. USB is a good solution for low bandwidth peripherals, while FireWire is a good solution for high bandwidth peripherals.


FireWire

Created by Apple, and also known as IEEE1394 (ie, it's an international standard) and i.Link, a name trademarked by Sony. The name FireWire will be used throughout this article. A high speed bus for serial data transfer. At present top speed is 400Mb/s, or 50MB/s.

The speed of the two FireWire ports on all new Apple Mac G3 pro computers (the ones in the snazzy blue and white cases with the handles on the corners) is 400Mb/s, although 100Mb/s and 200Mb/s (12.5MB/s and 25MB/s respectively) FireWire interfaces also exist on PCI cards and in some electronic equipment. (Any particular speed FireWire interface can also cope with the slower ones.) The iMac does not yet have FireWire, but the next major revision (in roughly five months time, at time of writing) is posted to have it included on the motherboard – one port only, though.

FireWire is hot-pluggable, meaning that equipment does not need to be turned off before plugging or unplugging. Up to 63 items can be connected to a FireWire bus. No terminators or IDs need to be set (unlike SCSI).

A new specification (IEEE 1394b) will double the technology's data-transfer rate to 800 megabits per second.

The main use of FireWire at present is between computers and digital video camcorders, where it is used to provide lossless transfer of video data directly from camcorder to computer (and back again) without any need to digitise the video information. Most camcorders use 100Mb/s FireWire. We may see this ability revolutionise video production, as even home users will be able to produce professional or near-professional quality edited video.

Hard disks are beginning to appear. Well, be released – hard disks don't normally just "appear." Epson has stated it will add FireWire to some of its higher-end printers.

Sony has just announced the release of a CD-RW drive with FireWire interface and has committed to using FireWire (under the name i.Link) in many other ways over the next few years. They plan to have basically all your higher-end home electronic equipment linked with it, from your computer to your stereo and video recorder. Samsung has demonstrated its Home Wide Web methodology for connecting consumer-electronics devices using standard IP protocols over IEEE 1394 links.

FireWire is not exactly unsuited for low data rate peripherals such as keyboards and mice – it could handle those very well – but since USB 1.1 is cheaper and was designed for those uses in mind, there's not much point in using FireWire for those things.

 


The FireWire symbol

"The FireWire word mark is an Apple trademark and must be licensed for use by third-parties. There is currently no licensing fee."
(At time of writing).

 


6 pin FireWire plug
(one pair for power,
two data pairs)

 


4 pin FireWire plug
(one pair for power,
one data pair)


USB 1.1

Acronym for Universal Serial Bus, version 1.1. Current speed is 12Mb/s or 1.5MB/s, although usable throughput is 6-8Mb/s. Contrary to popular belief, Intel didn't invent USB. They bought it from a single person who developed it while working at a company called Entrega. Since then it has been marketed by Intel with support from some other companies, for the purposes of telephone interconnectivity, ease of use (plug and play), and ease of expansion. All USB 1.1 features are also found in USB 2.0.

USB is hot-pluggable, meaning that equipment does not need to be turned off before plugging ing or unplugging. Up to 127 items can be connected to a particular USB. No terminators or IDs need to be set (unlike SCSI). USB hubs allow for downstream spreading.

Due to the slower speed of this bus, it is ideal for peripherals such as "telephone/fax/modem adapters, answering machines, scanners, PDA's, keyboards, mice, etc." Many printers also use USB. The typical small data transfer rate necessary for all of these uses make USB worthwhile.

This bus is unsuitable for internal or external hard disk storage due to the higher data transfer rates needed. Note that problems may be experienced attempting to burn a CD-R at 4x speed due to the 600kB/s bandwidth needed – a rate less than half of the maximum USB bandwidth.Also note that problems may be experienced with running USB peripherals in addition to high-bandwidth devices such as speakers. (If the speakers are plugged in first they may use all available bandwidth.)

Note that USB (any version) has not been adopted as a standard by the IEEE or any other independent standards organisation. However, because of USB 1.1's applicability for certain uses (not catered for by FireWire) and also largely due to its adoption by Apple last year (1998 with the release of the iMac), USB 1.1 is currently undergoing a surge in popularity.


USB 2.0

An initiative by Intel and various other companies (including Microsoft) to develop a higher speed version of USB led to the release of a plan for USB 2.0. Projected speed is 10 to 20 times the speed of USB 1.1, or 120Mb/s to 240Mb/s (15MB/s to 30MB/s). Planned release is 3rd quarter 2000. It is planned that USB 2.0 will be "forward and backward compatible" with USB 1.1. (Anyone know what forward compatibility with a previous version is?)

Presumeably USB 2.0 is Intel and Microsoft's answer to Apple's FireWire. However, there are concerns from a number of areas that USB 2.0 will be either pointless or counterproductive, for the following reasons.

  • Due to the large difference in speed of the two buses, running peripherals of both USB 1.1 and USB 2.0, this will not be a small problem, and may mean expensive hardware to overcome.
  • Buses with USB 1.1 and USB 2.0 devices on them will have the data bandwidth split between the two versions. This means that USB 1.1 will have 6Mb/s bandwidth and USB 2.0 will have 60Mb/s to 120Mb/s, assuming a 50:50 split. "... with bandwidth of up to 240Mbps--a speed faster than wide SCSI-2 or narrow ultra SCSI-3." Yes, but not if there are USB 1.1 peripherals on the same bus.
  • Hubs will be rather complicated and expensive due to the need to convert downstream USB 1.1 to upstream USB 2.0 in order to keep the problem mentioned in the previous point to a minimum. Bear in mind that few, if any, manufacturers will incorporate USB 2.0 into keyboards, mice, and joysticks. (This may mean that PCs will have separate USB 1.1 sockets expressly for those items. More cost.)
  • By the time USB 2.0 will be ready to go to market, FireWire may well have a bandwidth of between 800Mb/s and 1600Mb/s.
  • The USB architecture is not peer-to-peer, so all data needs to go through the CPU. This effectively halves the usable data bandwidth since data is moved twice if going from USB device to USB device. Using an example to illustrate, this means that data transmitted by a scanner has to go through the CPU before it could be stored on a USB zip disk.
    • Taking a best case scenario for both buses, 240Mb/s for USB 2.0 with no USB 1.1 devices connected, compared to 1600Mb/s for FireWire doesn't look like a very good comparison. Since a worst case scenario for USB 2.0 means it never gets to market, an actual worst case figure could easily be 30Mb/s (3.75MB/s – not fast enough for AV work, and yet at Intel's Developer Forum in March and again at WinHEC, Intel executives said they intend that USB 2.0 will replace SCSI in PCs).
    • Even the best conceivable USB 2.0 speed is just over half of the present FireWire speed, which makes one wonder why they are bothering.
  • USB 1.1 cables and connectors will not be reliable enough to take the higher data rates of USB 2.0, so new, more expensive cabling will be required – for your whole peripheral network
  • The USB 2.0 standard is designed with a single hard disk drive in mind. Forget arrays.

To summarize, USB 2.0 seems to serve no real purpose, as it will be slower and possibly more expensive than already existing technologies. In the USB 2.0 "backgrounder" they state:

I/O connectivity is being further advanced with the IEEE 1394 standard. USB 2.0 and 1394 primarily differ in terms of application focus. USB 2.0 will support the full range of popular PC peripherals while 1394 targets connection to audio visual consumer electronic devices such as digital camcorders, digital VCRs and digital televisions.

This is deliberate misinformation, but since it could be called corporate warfare, I'll stop short of calling them liars. However, when they released the original USB, these same people apparently recognised that FireWire is suitable for all medium and high-speed computer peripherals and other electronic equipment such as stereos – that's one of the reasons they only aimed at the low speed end of the bus market. OK. They are liars.


Politics

Political shenanigans then? The answer probably comes when we look at some of the other companies who are supporting Intel.

Philips Digital, who strangely enough are also in the group of companies who have embraced FireWire, probably just confuse the issue. Maybe they don't understand FireWire. Maybe they have other weird reasons (ie, ulterior motives).

Also in the group of companies with Intel and Microsoft are Hewlett-Packard and Compaq. Here possibly lies our answer. Both these PC manufacturers have complained loudly and bitterly about Apple's licencing scheme for FireWire. Without going into whether the scheme is right, these companies appear to have supported the USB 2.0 specification at least partly in an attempt to get Apple to review its licensing scheme, which involves a $1 levy per FireWire port for late adopters of the technology (which includes Hewlett-Packard and Compaq).

'Nuff said. Let's just wait and see if USB 2.0 ever does eventuate (and how well it'll work if it does) and if Apple decides to change its pricing for FireWire.


Extra Reading

FireWire articles:

Pro-USB 2.0 info:

Two articles pointing out some of the problems with USB 2.0:

  • Mac Weekly Journal article.
  • TechWeb article."When USB 2.0 was announced at the Intel Development Forum to a partisan crowd of 2,000, only one person applauded. No wonder." – James Snider, worldwide strategic marketing manager for bus solutions at Texas Instruments Inc, is chairman of the 1394 Trade Association.

Firewire vs USB 2.0 real world tests (Added 5 April 2003):

  • TechTV's three page article "USB 2.0 Versus FireWire" from 29 July 29, 2002:
    "Despite USB 2.0's 80 Kbps speed advantage over FireWire, our testing showed that the additional overhead of USB 2.0 made it slower than FireWire. For high-bandwidth devices such as external hard drives, the difference was as high as 70 percent." That is, Firewire was as much as 70% faster than USB 2.0 in real world tests. The sum it up nicely: "FireWire remains the performance king of plug-and-play connections"

Related articles:

  • EETimes article featuring JVC and Sony pushing D-VHS on FireWire networks as the most practical home video solution. "One tape can record for 7 hours in standard-definition mode at a transfer rate of 14.1 Mbits/second, and 3.5 hours in high-definition mode at 28.2 Mbits/s." 44Gbyte per tape, BTW.
  • EETimes article featuring Texas Instruments' release of a new chipset for FireWire. "... the chip is part of 'our aggressive move to dominate the 1394 PC space,' said Larry Blackledge, bus-solutions business manager at TI."


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