March 15, 2011 by Dave

A little while ago, I posted this question on SuperUser, asking the computer-savvy community of system administrators, power users, and os gurus if they had any ideas:

Does anyone know of any software/hardware configuration that will allow you to preview/view the contents multiple monitors on one monitor? Let's pretend:

  1. I have two monitors hooked up to one pc, Monitor A and Monitor B. The monitors are not near each other.
  2. I'd like to be able to preview/see what's displaying on Monitor B on Monitor A

I haven't been able to find much about this, but I imagine it may not currently be possible to access/emulate video output going out of a video port in software.

However, wouldn't it be possible to capture display data generated by the OS kernel or data getting passed down to the display adapter driver?

I asked this question because I had a computer that had two displays hooked up to it, and I wanted to see what was going on with both monitors at the same time. Normally dual displays sit right next to eachother, but in my setup, the displays were located on opposite sides of a wall.

I got some answers with different clever approaches to this conundrum. However, a suggestion by nhinkle stood out to me: Why don't I use a VNC server?

Well, that's exactly what I did, and the results were pretty good. If you're not familiar with vnc(a type of open, cross-platform remote desktop management), it allows other computers to log into your computer(the server) and see your desktop, open applications, etc. Most VNC servers are cross-platform(which means they run on a variety of operating systems), but in this setup I'm running 64-Bit Windows 7(Ultimate).

After testing a few VNC servers that boasted "Multiple Monitor Support", like UltraVNC and TightVNC, I found the easiest one to use was TightVNC. After a few easy steps, I was able to launch a VNC server on my local machine, and then connect to my computer...with my computer.

I know it feels weird using your computer as both the server and the client to connect to itself, but just power through it!

Here's what I did.

Step 1: Setup The VNC Server

Start up the TightVNC Server(I used application mode since I may not run this all the time). Open up the Configuration settings for the server and click on the Access Control tab.

Check the box in the Loopback Connections section that says Allow loopback connections. Without this setting checked, you won't be able to connect to the server from the same computer as the server. Hit OK, and your server will start running.

Step 2: Connect with the Client

Next, Start the TightVNC Viewer.

In the box that specifies which server you'll be connecting to, just enter in localhost and click Connect, enter your password, and blam! You're connected. 

One of the cool things about TightVNC is that you don't have to specify multiple displays, they are displayed automatically. The client has scrollbars that will let you scroll to the other displays. Nice!

Here's a screenshot of my entire desktop, with the vnc client running in 25% scale mode:

Ignore the ugly custard background...that's uh...compatibility mode. I like to scale my client down to 25%(so it doesn't fill my entire screen). You can also turn on View Only Mode if you want to speed things up and you're not planning on interacting with your display through the client.  To change these, right click on the Client's title bar, and click Connection Options. Here's what mine look like:

That's all there is to it! We now have our VNC Client that's displaying all of your multiple monitors. Just move the client window to your main display, and now you can see what's going on with your other displays. Cool, eh?





Oct 27 2011 at 05:34 PM

awesoma thanks!


Feb 16 2012 at 06:44 AM

Great article. Most VNC documentation doesnt explain what scaling is very well but you have covered it well here. Thanks

Add A Comment

Completely Private, used for Gravatar