Over the last few years, devices using USB ports have swept virtually all other connection types from store shelves - and that's a good thing. You no longer need to worry about choosing between serial or PS/2 mice, parallel port or SCSI scanners, parallel or serial printers - USB rules! However, there are still a few potential gotchas to consider when wading through holiday shopping crowds on a mission to pick up a USB device for your favorite computer user. These include:
There are three places you can plug in a USB device:
If you want to avoid problems, the first option's the best. With rare exceptions, USB ports built into your system provide a full 500 milliamps (mA) of power per port, the maximum power amount required for many of today's most popular USB devices like portable hard disks and flash memory. But, if you're short of USB ports, it's time for a hub.
A bus-powered hub might seem easier to use, because it doesn't use an AC adapter. Unfortunately, because it is powered by the upstream USB port, a bus-powered hub provides only one-fifth the power of a self-powered hub: just 100 milliamps (100mA) per port.
100mA is enough power to run most mice and keyboards, as well and devices with their own AC power source, such as 3.5-inch external hard disk drives, printers, and scanners. However, guess what USB devices are most likely to be stocking stuffers this year? USB flash drives and 2.5-inch hard disks! They need 500mA of power to run. A well-behaved device will complain (via the notification area) if there's not enough power, but I have seen a USB flash drive contents destroyed by plugging it into a bus-powered USB hub. Ouch!
By the way, if you're wondering how much power your USB devices use in Windows, open Device Manager and expand the Universal Serial Bus controllers category. Open the properties sheet for each USB Root Hub and Generic USB Hub, click the Power tab, and you will see the power usage for each device and the amount of power available per port. Some devices don't draw much power, and are happy with any type of a USB connection:
However, portable USB drives and flash memory devices top the list of power-hungry devices that expect a full 500mA of power on the USB banquet table:
To learn how to cope with reduced root hub power on some systems, read on.
Big-box electronics retailer Circuit City is selling a Belkin USB 1.1 hub for $5.99 today, and Staples is offering a $9.98 Targus USB 1.1 mini hub this weekend. - but no amount of savings can make up for stifling the performance of your USB 2.0 devices by plugging them into a USB 1.1 hub. To make matters worse, these hubs don't include external power supplies, so they can't support devices that require more than 100mA per port.
USB 1.1 devices like these are gifts that keep on giving...frustration.