USB is an interconnection standard which become very popular in the late 1990's in consumer PCs, for connection of slower-speed peripherals such as keyboards, mice, and digital cameras. Its main attractions are relatively low cost and hot-pluggability.
USB is a "host / device" protocol. That means that a USB cable has two different plugs at its ends, one ("A-series") for connection to the host (computer), and the other ("B-series") for connection to the device. It is not possible to connect the USB ports of two computers together (since they're both A-series), nor is it possible to connect the USB ports of two devices together (since they're both B-series).
The USB Specs: 1.1 and 2.0
Full-Speed 12 Mbps Low-Speed 1.5 Mbps
Low Speed was entirely suitable for keyboards and mice, and Full Speed was useful for digital cameras and 10Base Ethernet. But it was useless for hard drives, CD-R burners, much less real-time recording of audio. With FireWire already in existence at 400 Mbps (33 times faster than USB Full Speed), it rapidly became clear that USB needed a higher data rate for the interface to be taken seriously for data transfers.
The next major release was Rev 2.0, which added a new optional "High Speed" mode:
High-Speed 480 Mbps Full-Speed 12 Mbps Low-Speed 1.5 Mbps
The new faster speed required new hardware — none of the older USB 1.1 ports would work at High-Speed. But new USB 2.0-compliant ports would be back-compatible with the older USB 1.1 ports (at Full-Speed), so at least the new revision did not obsolete the large number of USB 1.1 hosts and devices already in the field.
USB 2.0 and High-Speed Are Not The Same
It is important to note that the statement "This device has USB 2.0" does NOT mean "This device supports High-Speed". It means "This device is compliant with Rev 2.0 of the USB spec, in which High-Speed support is optional". It is entirely legit for a product to be "USB 2.0" and still only run at "Full Speed", not "High-Speed".
There was considerable argument within the USB Implementors' Forum (USB-IF, see below) that this would cause confusion among consumers. Indeed, if you ask 100 people who have heard of USB 2.0, "What does that mean about this product?", 99 of them will reply, "It means it runs at High-Speed". WRONG ANSWER.
The right answer is: "It means it MIGHT run at High-Speed". The 1 person in 100 who knows better is typically a technoid geek (or a Glyph employee) who reads carefully. And now, YOU know better.
What this means to YOU is: When you buy a USB-capable device that you want to run at High-Speed, make sure if it says "USB 2.0" it ALSO says "High-Speed", AND also look for the special USB "certified" icon that shows the red "HI-SPEED" swoosh:
USB Icon USB High-Speed Icon
The only drawback to looking for the icons is that the USB-IF demands money (a lot if it) from manufacturers who want to display the USB icons. Some manufacturers would rather save the money and not use the icon even though their products are compliant, because then they can sell their products for less (remember — USB is often used on inexpensive products...). So unfortunately, although presence of the icon means compliance, lack of the icon does not necessarily mean non-compliance; it might only mean that the manufacturer didn't want to ante up USB-IF's fee for licensing the icon.
USB's new High-Speed mode was not supported by the existing 1.1-compliant USB devices, and at first no computers had USB High-Speed host ports either, so it took a little while to catch on. These days, you can generally assume that the USB ports on new computers are probably 2.0-compliant and also probably support High-Speed mode. But you know what "assume" means...
There are still a lot of new devices sold with USB 1.1 only, or with USB 2.0 but no High-Speed support, meaning they can only go at Full-Speed or Low-Speed. Beware — look for the red swoosh on the USB icon — and read the fine print.
USB 2.0 High-Speed (400 Mbps) vs. FireWire (480 Mbps)
When USB 2.0 defined High-Speed at 480 Mbps, there was some speculation that the choice of 480 Mbps was made specifically so that USB could claim speed superiority over FireWire "A" (FireWire IEEE-1394a is 400 Mbps). In fact the two rates work out to be about equivalent for large data transfers, since FireWire's protocols are somewhat more efficient than USB's for large transfers and that evens up the race. There are instances where FireWire 1394a beats USB High-Speed, and vice versa.
In 2003, FireWire "B" (IEEE-1394b) is going to reach 800 Mbps and that will leave USB 2.0 High-Speed more or less in the dust yet again. But for most non-critical audio applications, USB 2.0 High-Speed will work acceptably.
Glyph's Position
Glyph's primary interfaces of choice are FireWire, SCSI, and Fibre Channel, because these are the interfaces available in serious audio and video recording environments. USB 2.0 is not widely used in those environments, because at its best USB 2.0 is only about the equal of FireWire, the slowest of the three primary interfaces. Granted, some consumer and "pro-sumer" gear has USB 2.0 because it is less costly than FireWire. But there's no screaming need to provide USB-only support for our market at present, since the existing interfaces have the bases pretty well covered.
USB 2.0 High-Speed is a useful interface for backing data up, and for transferring data to other computers which might only have a USB 2.0 port and no FireWire, SCSI, or Fibre Channel. Therefore, Glyph has made USB 2.0 High-Speed available as an option in addition to FireWire, on our lower-cost products which could be carried into environments where only USB ports exist (mainly, consumer Windows computers). We encourage use of the FireWire ports for audio recording applications; the USB ports are suggested mainly for use as backup and archiving to computers that don't have FireWire ports. A drive that has both FireWire and USB 2.0 ports can be used with either kind of bus, but NOT both at once. That is, it cannot be active as a FireWire device at the same time it's active as a USB device. One at a time, please.
Glyph's primary focus is audio and video recording, and so FireWire will remain our main interface at the lower-speed end of the spectrum, with SCSI in the mid-range, and Fibre Channel at the high-speed end.
Useful Links
USB-IF (Implementors' Forum)USB FAQ
USB 2.0 Specification (zipped PDFs)
USB 1.1 Specification (zipped PDFs)