Review: Three external screens from a single laptop with help from DisplayLink

As a developer I’ve become used to multiple monitors to increase my productivity.  Debugging applications is much easier when one monitor is running Visual Studio and a second monitor is displaying the application being debugged, or SQL Management Studio, or your Locals window.

When I plugged my latest HP 6910p laptop into the docking station I was amazed to find that it supported dual external displays; both the DVI and analogue VGA ports can be active simultaneously.  It’s a real advantage to get off the laptop display which I never find ideal when working at a desk.  You really need the two monitors to be arranged side by side rather than above each other.  This places the laptop much further away than normal and makes the screen hard to read. 

I’ve been using dual 17” monitors at 1280 x 1024 with my laptop/docking station combination for some time.  A few months ago I bought a 24” HD screen, 1920 x 1080.  The ‘spare’ 17” monitor was relegated to my old desktop system, used for monitoring Outlook and Messenger and for Media Player duties.

If only I could have all three screens connected to my laptop ...

Enter DisplayLink

For some time, there have been proprietary graphics solutions for laptops which use PC Cards using the CardBus and Zoomed video abilities.  Effectively you are adding a new graphics card to the system.  These tended to be expensive and there was always the worry about driver availability for new operating systems.

DisplayLink takes a different route to enabling an external display by using a USB 2.0 interface.  A desktop graphics driver delivers compressed video to a dedicated hardware decoder which has an analogue VGA output.  Not only does this make it available to any laptop with USB 2.0, it also supports desktop systems without upgrading the main graphics card.

Cheap route to DisplayLink

I’d actually been following the progression of DisplayLink for some time in various reviews, from the expensive Village Tronic ViBook ( at £130 to the more reasonable Kensington Dual Monitor Adapter ( at £60.

Also, companies like Samsung have been selling external monitors which include smaller secondary screens powered by DisplayLink, as well as high end digital photo frames which include DisplayLink connectivity.

However, one of the PC Pro reviews included the comment it might be a better idea to search eBay for a Kensington USB docking station which supports video as these are normally available for less than the dedicated solutions.

 My hardware

I spent a few months on eBay tracking Kensington docking stations with video, for the ‘right price’, and last week I finally won one in an auction for £20.  The unit came with a power adapter, USB lead and the actual docking bar itself.  In addition to DisplayLink the bar provides a 4-port powered USB 2.0 hub, audio and 10/100 networking

Docking Station - Front

Docking Station - Front

Docking Station - Back

Docking Station - Rear

The great news is that if all you are using is the DisplayLink connecter there is no need for the power adapter as the USB 2.0 connection provides the power.

The laptop is a HP 6910p (with 128Mb ATI Mobility Radeon X2300), 2.2GHz Core Duo, 4Gb RAM, with the advanced docking station providing simultaneous DVI and VGA outputs by default when the laptop lid is closed.

Drivers for Windows 7 RC 64-bit

One of my criteria for using DisplayLink was that the software had to work under Windows 7 as, since the beta release this has become my day to day operating system on my laptop.  Even worse, it is a 64-bit installation which always makes one more wary of driver compatibility.

The good news was that the software drivers are available from the guys who make the hardware chip at rather than from Kensington.  I thought I might be able to use a Vista 64-bit driver, but on the driver download page was a warning that it was not compatible with Windows 7.  But right next to that warning was a link to a specific Windows 7 Preview driver.

By the time I finally won a Kensington docking station from eBay at the ‘right price’ my laptop had been upgraded to Windows 7 RC and the DisplayLink Windows 7 driver software had also been updated to a new release on 3 April 2009.

As with most USB devices, I ran the driver setup first (no reboot required) before plugging in the docking station.  Various new hardware devices were detected, including the DisplayLink adapter. Only an AX88772 device wasn’t recognised, the ASIX USB 2.0 LAN controller.

A quick right click on the desktop, Screen Resolution, and there were three monitors on one laptop.

Screen Resolution Dialog

I enabled the monitor and took my first photo of three monitors running live on one laptop.

Three monitors rocks !


DisplayLink utility

Although you can configure the resolution and layout of the monitors within the standard Screen Resolution dialog, there is a special DisplayLink utility.  This is installed during the driver setup but on my system was not added to the Start Menu.  I found the utility files in, \Program Files\DisplayLink Core Software.  Running DisplayLinkUI.exe provides a new icon in the system tray/notification area where you can control the DisplayLink specific options.

DisplayLink - Colour Depth

Colour Depth
DisplayLink - Resolution

DisplayLink - Rotation

Rotation Options

During writing this blog post I decided to test whether the standard Windows 7 screen rotation options could be used instead of the DisplayLink utility menu.  Big mistake, my other two displays went blank and it took a few dock/undocks and a DisplayLink driver uninstall and reinstall to get everything back to normal.  Admittedly both Windows 7 and the DisplayLink drivers are both beta software so I’ll forgive them as long as the final releases work as expected.

CPU utilisation

The big downside with DisplayLink is that it uses the system CPU to compress the video it is sending to the hardware decoder.  Kensington recommend at least a dual core CPU running at 1.2GHz and above.  You do notice a bit of screen lag compared to the ‘real’ monitors but for applications like Outlook and Messenger work fine.

I decided to do a bit of simple benchmarking using Task Manager, tracking the core Display Link process, DisplayLinkManager.exe (you need to click on Show Process From All Users to view this).

Here are the results of my simple CPU utilisation tests,

Outlook and Messenger running in background                 < 1%

Windows Media Player playing MP3 files                              10% iPlayer video within a web page                           15%

(Turkish Grand Prix 2005)

Windows Media Player MPEG4 video                                     30%

(Sebastien Lambla ASP.NET MVC best practices from VistaSquad user group)


What I wanted was a simple and cheap solution to providing a third display for my laptop which could handle background applications such as Outlook, Messenger or Twitter without compromising general performance.  I’d say DisplayLink has achieved that with an elegant solution to a simple problem, all for £20 delivered thanks to eBay.


Print | posted on Wednesday, June 3, 2009 11:07 AM

Comments on this post

No comments posted yet.

Your comment:

 (will show your gravatar)