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How Does Windows Handle USB Devices?
Written by Dave Gerber, Program Chair, Sarasota PCUG, Florida; member of the “Live on the Internet” Bits and Bytes radio show team
Dave_bytes(at)comcast.net
http://www.davebytes.com

One subject that often comes up is how Windows handles USB (Universal Serial Bus) devices and what you can do when USB devices don't work as you expect. First, let's talk about the two versions of USB that you'll probably encounter:

USB 1.1: these were the first widely-available devices and usually ran at a speed of 1.5 mb/sec. They were meant to replace old-fashioned serial and parallel (printer) connections that ran at only a fraction of the speed and could connect only one device at a time. While this speed was OK for slow devices like mice and keyboards, it wasn't useful for transferring large amounts of data, like from digital video cameras. For faster speeds, you needed SCSI or FireWire (IEEE 1394) connections. Since these were used mostly on the Mac, you often needed an add-in card for your computer to use them, which is one of the inconveniences that USB was supposed to alleviate.

USB 2.0: typically runs at the much higher speed of 480 mb/sec, which is faster than the original FireWire standard and much faster than SCSI. This is more appropriate for large data transfer, such as to external hard drives, and necessary to connect CD or DVD burners. However, some people still prefer FireWire for devices like video cameras, because FireWire is really a network that allows devices to be more interactive.

So how do you know which USB you have? If your computer was made sometime in the last few years, chances are its USB ports are version 2.0, which are backwards-compatible with 1.1 devices. One way you can tell which version your computer has is to look at the Device Manager in Windows XP:

•	Press Windows Key + Break to open Device Manager (or click the Start button, then right-click My Computer and select Properties).
•	Click the Hardware tab, then click Device Manager.
•	At the bottom of the list, click the plus sign next to Universal Serial Bus controllers.

If your computer has is equipped with USB 1.1, you'll see a device or two called a Host Controller or Open Host Controller. 

If your computer is equipped with USB 2.0, you'll see a device or two called an Enhanced Host Controller or USB 2.0 Controller.

Any USB device you buy will have the regular USB trident logo and any high-speed USB device will have the red, white and blue high-speed logo. 

If you connect a high-speed USB device to a low-speed USB port on your computer, Windows will probably give you a message that the device can run faster if you connect it to a high-speed port. A USB 2.0 internal expansion card costs about $20 and a USB 2.0 notebook adapter (fits in the PC Card slot) costs about $40.

The most common problem people have is when they connect a USB flash drive (sometimes called a thumb drive) to a computer and the computer doesn't recognize it. 

First, let me say that these are great devices. Connect one to your computer and it works like a removable hard drive.

When you connect a USB device to a computer running Windows XP, the computer will detect it immediately. When that device is a USB drive, you'll probably see a message on the taskbar that Windows detected a new device, followed by a dialog box that asks if you want to open the drive to see its contents, play a movie and other choices. Windows will also assign a drive letter to the device. But sometimes you won't get this dialog box, and when you open My Computer manually ( Windows Key + E), you won't see the device listed. That means there's a drive letter conflict.

Here's how you fix it:

•	Select Start/Control Panel, then double-click Administrative Tools. (You may also have Administrative Tools directly on the Start menu.)
•	Double-click Computer Management.
•	On the left side of the Computer Management console, select Disk Management.
•	On the right side, you should see a device listed as a removable drive, probably with the same letter as another drive you're already using.
•	Right-click the white bar where it shows the letter, then select Change Drive Letter and Paths.
•	Select the letter, then click the Change button.
•	Pick a letter not already in use from the list, then click OK. 
•	Click OK on the warning message, then click OK again. (I assign U: to all USB flash drives, since I never use more than one flash drive at a time.)
•	Close the Computer Management console. When you go back into My Computer, you should see the USB drive with the new letter.

Another common problem is running out of ports. When USB started being implemented, the idea was that you would daisy-chain the devices together. So computer manufacturers would put in only two ports (always in the back) and only one port on laptops. For a variety of reasons, the daisy-chain idea never caught on, and computers made today typically have four ports in the back and two in the front, for quick access.

If you run out of ports, you can fix the problem -- as with so many others -- by applying cash. Buy an external USB hub for anywhere from $10 to $40, depending on size, number of ports and power. A hub will split a single USB port into several more. The better ones have their own power supply, so your devices don't have to rely on the computer for powering the USB connection. When there isn't enough power to go around for all the devices, they can go offline.

This brings me to the last problem I'll mention: USB devices going offline because of reasons unrelated to power shortage. This was fairly common when you had many devices connected using USB 1.1 in versions of Windows older than 2000, where the devices had to supply their own software to get USB to work. (Native USB drivers were first included with 2000, then made more robust in XP -- and Vista, presumably). If this happens, simply unplug all the USB devices, then plug them back in one-by-one. If any are daisy-chained together, connect the parent devices before connecting the child devices.

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