USB hubs catch attention of many people using desktop or laptops computers . Since most of the tools like digital cameras , flash drives , iPod , scanners etc can be connected to their computers easily through USB port ( if supported ) . But different devices have different power requirement and one can not get all of them to work properly if connected through one of these USB hubs . For example a digital camera or a scanner requires more power than a flash drive .
There are two types of USB hubs available . One is bus-powered and the other one is self-powered . Bus powered USB hubs receive all their power through the host computer they are connected . On the other hand a self-powered USB hub takes its power either from the PC power supply or has its own power supply .
To function correctly a single USB port requires current from 100 mA to 500 mA depending upon the device . So if a bus-powered 4 port USB hub ( shown in the above picture ) is used , each of its ports will get a maximum of 100 mA ( 100 mA for the port which is used to connect the HUB ) . If you connect any USB device to this HUB which requires more than 100 mA to operate then it will not work . No argument why I could not operate my web cam through the HUB shown in the above picture .
Many PC users are not aware of this simple fact and are obsessed by those cool looking USB hubs available at local PC stores . They buy those bus-powered HUBs and end up cursing themselves . If you really want a fully functional USB hub that will not cause you any trouble in connecting any USB device available then I suggest that you only buy one that is self powered . The good thing is that there is not much price difference between the two .