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.
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).
