CompTIA A_ Certification All-In-One Exam Guide, Seventh Edition - Michael Meyers [306]
Figure 18-11 USB hub Power tab
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NOTE The USB Hub Power Properties tab shows you the power usage only for a given moment, so to ensure you keep getting an accurate readings, you must click the Refresh button to update its display. Make sure your USB device works, and then refresh to see the maximum power used.
Most root hubs provide 500 mA per port—more than enough for any USB device. Most power problems take place when you start adding hubs, especially bus-powered hubs, and then you add too many devices to them. Figure 18-12 shows the Power tab for a bus-powered hub; note that it provides a maximum of 200 mA per port.
There’s one more problem with USB power: sometimes USB devices go to sleep and don’t wake up. Actually, the system is telling them to sleep, to save power. You can suspect this problem if you try to access a USB device that was working earlier, but that suddenly no longer appears in Device Manager. To fix this, head back in to Device Manager to inspect the hub’s Properties, but this time open the Power Management tab and uncheck the Allow the computer to turn off this device to save power checkbox, as shown in Figure 18-13.
Figure 18-12 General purpose bus-powered hub
Figure 18-13 Power Management tab
FireWire Ports
At first glance, FireWire, also known as IEEE 1394, looks and acts much like USB. FireWire has all of the features of USB, but it uses different connectors and is actually the older of the two technologies. For years, FireWire had the upper hand when it came to moving data quickly to and from external devices. The onset of Hi-Speed USB changed that, and FireWire has lost ground to USB in many areas. One area where FireWire still dominates is editing digital video. Most modern digital video cameras use the IEEE 1394 interface for transferring video from camera to PC for editing. The high transfer speed of FireWire makes transferring large video files quick and easy.
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NOTE Even Apple, the inventors of FireWire, dropped FireWire for USB in its iPod.
Understanding FireWire
FireWire has two distinct types of connectors, both of which are commonly found on PCs. The first is a 6-pin powered connector, the type you see on many desktop PCs. Like USB, a FireWire port is capable of providing power to a device, and it carries the same cautions about powering high-power devices through the port. The other type of connector is a 4-pin bus-powered connector, which you see on portable computers and such FireWire devices as cameras. This type of connector does not provide power to a device, so you need to find another method of powering the external device.
FireWire comes in two speeds: IEEE 1394a, which runs at 400 Mbps, and IEEE 1394b, which runs at 800 Mbps. FireWire devices can also take advantage of bus mastering, enabling two FireWire devices—such as a digital video camera and an external FireWire hard drive—to communicate directly with each other. When it comes to raw speed, FireWire 800—that would be 1394b, naturally—is much faster than Hi-Speed USB.
FireWire does have differences from USB other than just speed and a different-looking connector. First, a USB device must connect directly to a hub, but a FireWire device may use either a hub or daisy chaining. Figure 18-14 shows the difference between hubbed connections and daisy chaining. Second, FireWire supports a maximum of 63 devices, compared to USB’s 127. Third, each cable in a FireWire daisy chain has a maximum length of 4.5 meters, as opposed to USB’s 5 meters.
Configuring FireWire
FireWire was invented by and still controlled to a degree by Apple Computer. This single source of control makes FireWire more stable and more interchangeable than USB—in plain language, FireWire is ridiculously easy to use. In a Windows environment, FireWire is subject to many of the same issues as USB, such as the need to pre-install drivers,