CompTIA A_ Certification All-In-One Exam Guide, Seventh Edition - Michael Meyers [305]
Figure 18-9 Windows XP speed warning
Hubs also come in powered and bus-powered versions. If you choose to use a general purpose USB hub like the one shown in Figure 18-7, try to find a powered one, as too many devices on a single USB root hub will draw too much power and create problems.
Cable length is an important limitation to keep in mind with USB. USB specifications allow for a maximum cable length of 5 meters, although you may add a powered USB hub every 5 meters to extend this distance. Although most USB devices never get near this maximum, some devices, such as digital cameras, can come with cables at or near the maximum 5-meter cable length. Because USB is a two-way (bi-directional) connection, as the cable grows longer, even a standard, well-shielded, 20-gauge, twisted-pair USB cable begins to suffer from electrical interference. To avoid these problems, I stick to cables that are no more than about 2 meters long.
If you really want to play it safe, spend a few extra dollars and get a high-quality USB 2.0 cable like the one shown in Figure 18-10. These cables come with extra shielding and improved electrical performance to make sure your USB data gets from the device to your computer safely.
USB Configuration
The biggest troubleshooting challenge you encounter with USB is a direct result of its widespread adoption and ease of use. Pretty much every modern PC comes with multiple USB ports, and anyone can easily pick up a cool new USB device at the local computer store. The problems arise when all of this USB installation activity gets out of control, with too many devices using the wrong types of ports or pulling too much power. Happily, by following a few easy steps, you can avoid or eliminate these issues.
The first and often-ignored rule of USB installation is this: Always install the device driver for a new USB device before you plug it into the USB port. Once you’ve installed the device and you know the ports are active (running properly in Device Manager), feel free to plug in the new device and hot-swap to your heart’s content. USB device installation really is a breeze as long as you follow this rule!
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NOTE There are exceptions to the “install the driver first” rule. USB thumb drives, for example, as you will recall from Chapter 13, “Removable Media,” don’t need extra drivers at all. Just plug them in and Windows picks them up. (Technically speaking, though, that means the drivers came preinstalled with the operating system!)
Figure 18-10 USB 2.0 cable
Windows 2000, XP, and Vista have a large number of built-in drivers for USB devices. You can count on Windows 2000, Windows XP, and Windows Vista to recognize keyboards, mice, and other basic devices with their built-in drivers. Just be aware that if your new mouse or keyboard has some extras, the default USB drivers will probably not support them. To be sure I’m not missing any added functionality, I always install the driver that comes with the device or an updated one downloaded from the manufacturer’s Web site.
When looking to add a new USB device to a system, first make sure your machine has a USB port that supports the speed you need for the USB device. On more modern PCs, this is likely to be a nonissue. Even then, if you start adding hubs and such, you can end up with devices that either won’t run at all or, worse yet, exhibit strange behaviors.
The last and toughest issue is power. A mismatch between available and required power for USB devices can result in nonfunctioning or malfunctioning USB devices. If you’re pulling too much power, you must take devices off that root hub until the error goes away. Buy an add-in USB hub card if you need to use more devices than your current USB hub supports.
To check the USB power usage in Windows, open Device Manager and locate any USB hub under the Universal Serial Bus Controller