Hardware, Technology

How-to: Buy the Right USB Hub

Bus-powered USB hubI 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, addressing 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 transformer 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

About Allan J. Smithie

Allan J. Smithie is a journalist and commentator based in Dubai.


3 thoughts on “How-to: Buy the Right USB Hub

  1. It’s worth adding that devices such as USB external hard drives vary in power usage. A 3.5in drive is a big power drawer that usually requires it’s own power supply regardless of a dedicated USB port. A 2.5in (laptop) drive is usually low powered and will work through USB-power without having it’s own mains adapter. Plug it in alongside several devices on a hub and the 2.5in drive may also struggle to draw sufficient power.

    There is no support (that I am aware) of prioritising or switching out connected USB devices when several are attached to a standard retail external hub. USB switchers are specialist rarities and are themselves mains powered. RC

    Posted by Robin Catling | Sep 8, 2011, 1:22 am
  2. How to do tell which hubs are low powered and which will draw sufficient from the host?

    Posted by Yorton | Jun 4, 2012, 7:46 am
  3. Nice website over here! I’ll just wanna say thnx for that.

    Posted by M Angels | Jun 11, 2012, 2:03 am

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