I just bought a USB hub (Universal Serial Bus) for a old laptop that now spends most of it’s time at home as a general purpose work-horse PC. At least, that’s the intention, except it only has two USB ports, one of which is taken by the mouse. Printer, scanner, USB-sticks and various other gadgets demanded more, so I finally bought a cheap USB hub.
A USB hub is a device that exploits the USB daisy-chaining capability to expand a single USB port into several, providing more ports to connect devices to a host machine. The hub acts as a USB controller, adressing and managing traffic from multiple lanes through the one entry-way into your PC…
External USB hubs can be a chunky box looking like a network hub, or a dongle type for maximum portability. What you need to consider is the hub type rather than its’ size and shape. USB was designed as a power-efficient – that is, low-energy – port. The power supply over USB should be enough to run one high-powered device – a scanner or a TV tuner, but probably not a printer or stills camera. therefore it’s important to know what you’ll be plugging in and what type of hub you’ll need.
There are two types of USB:
- Self-powered hubs have a built-in power supply with a power supply jack and usually a transfomer to connect to the mains electricity.
- Unpowered (bus-powered) hubs draw their power from the host USB port into which they are plugged. An external bus-powered hub has only USB ports, no external power jack. Bus-powered hubs may be built into other peripherals, including keyboards, screens, printers, scanners.
While bus-powered hubs are generally cheaper, smaller and don’t require a power supply (making them ideal for use on laptops away from home), here may be a limit to the number of devices that can be used at once, depending on how much power each piece of hardware requires. If a device stops working or runs intermittently, it is likely that the combined power draw through the hub is more than the host USB hub can provide. It may be necessary to remove USB peripherals from the hub in order to continue running the one you want. Upshot: get the wrong type of hub and you’ll be no better off.
High-powered peripherals require over 100mA of power, according to the USB specification, which includes digital video cameras and hard drives. Low-powered hardware includes keyboards, mice, memory-card readers and game controllers. AJS