Windows 8 : Managing hardware devices - Enabling and disabling hardware devices, Monitoring USB devices

2/22/2014 3:30:48 AM

Enabling and disabling hardware devices

Not all hardware has to be enabled all the time. In fact, as you work on troubleshooting hardware in your organization, you might find it necessary to disable a device if it is causing problems. Then, after you correct a problem, you must bring the device back into operation.

To disable and enable devices, open the Device Manager by using one of the methods discussed previously in this chapter. Open the Properties page for the device you want to enable or disable and navigate to the Driver tab. From there, click either the Disable button (if the device is presently enabled) or the Enable button (if the device is presently disabled).

In Figure 1, note that the Disable button is currently available.

Disabling devices that are causing problems

Figure 1. Disabling devices that are causing problems

Monitoring USB devices

Most devices that employees in your organization attach to their computers are USB-based. Such devices include keyboards, mice, cameras, and thumb drives. USB is so popular because it’s so easy to use. In many cases, all you have to do is plug in the device, and it just works. This is for two reasons. First, many common devices already have generic drivers loaded in Windows. When the device is plugged in, Windows already knows how to handle the hardware. Second, USB ports, in addition to enabling communication between the device and the computer, also provide power to the connected device. That’s why you don’t need to plug a thumb drive into a power source when you connect it to the computer.

Although some of the devices you use are connected directly to USB ports in the computer, others might be connected through a USB hub. There are two varieties of USB hubs:

  • Self-powered A self-powered USB hub has a power supply that connects to an electrical outlet. These kinds of USB hubs provide their own power to connected devices.

  • Bus-powered A bus-powered USB hub gets its power from the system’s USB connectors and passes along that power to connected devices. The amount of available power in this scenario is more limited than it is with self-powered hubs.

USB devices can operate at multiple speeds, and each speed is based on a different USB standard. Different devices conform to different standards. Modern computers often include USB ports that operate at multiple speeds. For example, a single computer might include ports that operate at both USB 2.0 and USB 3.0 speeds. Here’s a look at the different standards and the speeds at which each operates:

  • USB 1.0/USB 1.1 Operates at a maximum speed of 12 megabits per second (Mbps)

  • USB 2.0 Operates at a maximum speed of 480 Mbps

  • USB 3.0 Operates at a maximum speed of 5 gigabits per second (Gbps)

Bandwidth is an important factor in USB troubleshooting, particularly when you’re dealing with older USB 1.0 or USB 1.1 systems. If there isn’t sufficient bandwidth to support the devices on a particular USB port, users can receive error messages such as “USB controller bandwidth exceeded.” When this happens, devices might not operate correctly.

Many devices will report to Windows the amount of bandwidth they use on the Advanced tab of the device’s Properties page in Device Manager. However, this is not true for all devices. This makes troubleshooting bandwidth issues a best-effort task rather than a scientific one. Fortunately, with the rise of USB 3.0 and a maximum bandwidth of 5 GHz, bandwidth issues are not as serious as they once were.

As mentioned previously, USB devices consume power from the USB bus. Therefore, it’s important to watch the USB port’s power budget to ensure that connected devices don’t surpass the power limit on the port. When you use a bus-powered USB hub to connect many devices, the possibility of exceeding this limit becomes more likely.

To view the current power usage on a USB hub—even an internal one that just manages a computer’s physical USB ports—open the Device Manager Properties page for a USB hub. On that page, select the Power tab to see a list of the devices connected to the hub and the power required to operate each device (Figure 2).

Hub showing a device consuming 200 mA of power

Figure 2. Hub showing a device consuming 200 mA of power

  •  Windows 8 : Managing drivers (part 7) - Discovering the Driver Verifier utility, Adding device drivers to the driver store
  •  Windows 8 : Managing drivers (part 6) - Using the System Information utility - Viewing conflicting or shared resources, System Information highlights
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