USB 2.0 FAQ
Basic Questions and Answers for USB 2.0

How fast is USB 2.0?

USB 2.0 is 480 Mb/sec, 40 times faster than USB 1.1.

What are the benefits of Hi-Speed USB 2.0?

The higher bandwidth of Hi-Speed USB 2.0 will support the most demanding PC user applications, such as digital image creation and web publishing, where multiple high-speed peripherals will be running simultaneously. Hi-Speed USB 2.0 is expected to replace USB 1.1, which is already a ubiquitous connector on PC systems today for such peripherals as keyboards, mice, joysticks, removable storage, printers and scanners.

Is there a difference between Hi-Speed USB and USB 2.0? Which is the correct nomenclature?

There is a difference in Hi-Speed USB and USB 2.0. The difference is that the USB 2.0 Specification covers all three speeds 480 Mbps, 12 Mbps, and 1.5 Mbps. "Hi-Speed USB" refers to just the 480 Mbps portion of the USB 2.0 Specification. We now use the term "USB" to refer to the 12Mbps and 1.5Mbps speeds.

Since Hi-Speed USB 2.0 is now about the same speed as IEEE 1394a, don't they compete?

No. Hi-Speed USB 2.0 is expected to become ubiquitous on all PC platforms because it is more easily integrated into the core chipsets, at which time it will become the preferred connection for PC peripherals. IEEE 1394's primary target is audio/visual consumer electronic devices such as digital camcorders, digital VCRs, DVDs, and digital televisions. Therefore, the two connections will differ primarily in application focus.

Is Microsoft supporting Hi-Speed USB 2.0 in Windows XP?

Microsoft fully supports Hi-Speed USB 2.0, and has been working to develop driver support since its inception.

Will my PC today work with a Hi-Speed USB 2.0 peripheral product?

Assuming you have a PC that has USB 1.1, if you plug your Hi-Speed USB 2.0 peripheral into the USB 1.1 system, your system will perform at the USB 1.1 speed. If you would like to use High-speed USB 2.0, you will need to update your PC either by adding in a PCI add-in card or purchasing a new MB with a discrete host controller that supports Hi-Speed USB 2.0 and installing Hi-Speed USB 2.0 drivers.

If Hi-Speed USB 2.0 is 40X faster, why is it that a CDRW, for example, is only 6X faster?

The 40X speed improvement is specific to the bus. What this literally means, is that the bus is no longer the bottleneck in performance. The actual performance improvement for a given product is dependent on how fast that product can run. Over time, you should see product vendors improving their products to take advantage of the 40X bus.


I have a PC that runs Windows 98, can I still use Hi-Speed USB 2.0 products?

Yes, assuming first that you install a Hi-Speed USB 2.0 add-in card and you install a Hi-Speed USB 2.0 driver. Since Microsoft is only developing drivers for Windows XP and 2000, you will have to use a 3rd party vendor's drivers. In most cases, if you upgrade your PC with an add-in card, it will come with a Hi-Speed USB 2.0 driver install CD, that covers 98, 98SE, and ME.

How many devices can be connected to one host?

You may connect up to 127 devices to a single host.

How far away from a host can a peripheral be located?

The maximum cable length is 5 meters. Anything longer starts to cause problems due to propagation delays. Even if you violated the spec, it literally wouldn't get you very far. Assuming worst-case delay times, a full speed device at the bottom of 5 hubs and cables has a timeout margin of 280ps. Reducing this margin to 0ps would only give you an extra 5cm, which is hardly worth the trouble.

For USB 1.1 and USB 2.0 Fiber and Copper Extenders, go here.