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 USB Device Main Page
 Member's Discussion

Frequently Asked Questions on USB
Q1: Will I need special software to run USB?
A1: All Current operating systems support USB. Many devices get all of the software support they need from the OS, but there are some that will come with a floppy or CD with specialized drivers for that particular device. Don't worry about getting the right software because the OS's that support USB always know how to determine if anything else is needed and they will help you get the software loaded so the device works correctly. 
Q2: Is USB available on mobile computers in addition to desktops?
A2: USB is currently a key feature on virtually every new notebook. One great advantage of USB is that it allows notebook users to easily share peripherals
Q3: What kinds of USB peripherals can I connect to my PC?
A3: USB carries data at the rate of 12 megabits per second, which is sufficient for "medium to low-speed peripherals". This is a broad category which includes telephones, digital cameras, modems, keyboards, mice, digital joysticks, some CD-ROM drives, tape and floppy drives, digital scanners and specialty printers. 

USB's data rate also accommodates new generation of peripherals such as MPEG-2 video-base products, data gloves and digitizers and soon an interface for Integrated Services Digital Network (ISDN) and digital PBXs.

Q4: Does USB affect the cost of PCs and peripheral devices?
A4: No. In most PCs, its a standard device interface fitted at no extra cost. By eliminating add-in cards and separate power supplies which you may need to add external devices, USB can help make PC peripheral devices more affordable. 
Q5: How many USB peripherals can I connect at once?
A5: Technically, you can connect up to 127 individual USB peripherals at one time. Due to the fact that some devices reserve USB bandwidth, the practical maximum of devices is less than the theoretical maximum. However, PCI-USB add-in cards provide an independent USB bus to which even more peripherals can be connected
Q6: Where can I learn more technical details about USB?
A6: Technical presentations and other details are available from the USB Implementers Forum on the USB developers site, as well as directly from USB-IF member companies.
Q7: What does it mean when a product is USB compliant and why should I care?
A7: Compliance means products that are called USB products are really built to match the description in the USB specification. 

There are many ways to make sure products work together and many ways to see if they match the specification, but compliance testing is one of the most useful.
If you don't find a product on a list it does not mean there is anything wrong with that product, but if you do find it there you know that this manufacturer has put in a lot of effort to try to make sure that product matches the USB specification and has the best chance of working properly in a variety of applications. Please visit the USB Compliance Program page for more details.

Q8: How long of a cable can I use to connect my device?
A8: In practice, the USB specification limits the length of a cable between full speed devices to 5 meters (a little under 16 feet 5 inches). For a low speed device the limit is 3 meters (9 feet 10 inches).
Q9: Why can't I use a cable longer than 3 or 5m?
A9: USB's electrical design doesn't allow it. When USB was designed, a decision was made to handle the propagation of electromagnetic fields on USB data lines in a way that limited the maximum length of a USB cable to something in the range of 4m. This method has a number of advantages and, since USB is intended for a desktop environment, the range limitations were deemed acceptable. If you're familiar with transmission line theory and want more detail on this topic, take a look at the USB signals section of the developers FAQ.
Q10: How far away from a PC can I put a USB device?
A10: With the maximum of 5 hubs connected with 5m cables and a 5m cable going to your full speed device, this will give you 30m of cable (see section 7.1.19 for details). With a low speed device, you will be able to get a range up to 27m, depending on how long the device's cable is. With a straightforward cable route, you will probably be able to reach out 25m or so from the PC.

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understanding USB