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.
USB ports in a self-powered hub also provide a full 500 milliamps (mA) of power per port. By the way, the term "self-powered" is a bit of a misnomer: there are no atomic batteries or turbines inside a self-powered hub. Instead, a self-powered hub uses an AC adapter "briquette" that plugs into a wall outlet or surge suppressor. Most include four USB ports, but some include as many as seven.
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.
Comments are closed on this article
Loraine_Burchell
May 25, 2011 at 10:19am
This seems a smart shopping guide indeed! I mean it's not very difficult to buy devices using USB ports but sometimes some advice is useful. Nowadays though, you can find these devices anywhere and they are pretty cheap because there is a big competition out there. When I was in vacation last year and I was trying to chose one of the Shanghai restaurants to have dinner I was shocked to see so many computer stores in that area.
HeartBurnKid
November 27, 2007 at 10:31am
One thing that's incorrect about your guide is that there are self-powered USB 1.1 hubs floating around out there. They're still slow as molasses, but they will at least power your devices.
I've got one on my rig; makes for a cheap and handy place to plug in devices that don't need a ton of bandwidth, like keyboards, mice, gamepads, etc.
Marcus_Soperus
November 28, 2007 at 2:52pm
Thanks for pointing out that USB 1.1 hubs still have a place on some PCs. In this article, I was referring specifically to the "Black Friday" mini-hub offerings that lack AC adapters, but I appreciate the clarification that some USB 1.1 hubs do include AC adapters (I still have a USB 1.1 hub hanging around my shop).
My main gripe with the big-box stores pushing USB 1.1 hubs at this late date is that unwary consumers may buy them for use with all of their USB devices - and then wonder why their USB 2.0 devices are so slow.
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It's amazing how illogical a business built on binary logic can be.
RPGgddss
November 25, 2007 at 9:53am
I never knew there was so much to think about when buying USB stuff!
Jondi "RPGgddss" Schmitt
Your friendly neighborhood techie Tupperware lady
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