You’re probably well aware that you can plug an external monitor into your Macbook and use both the built-in display and the external monitors in a dual display configuration. Since your Mac only has one monitor port, it would seem that one external display is the maximum, but there are ways around that limitation. I’m going to describe the solution I found, but I’m going to warn you right now that my solution may not be for everyone.

The physical setup

My primary computer is a three year-old MacBook Pro, and I have a Windows XP desktop computer that lives under my desk. It’s an older box that I keep around for occasional tasks that I’d rather not run on my production laptop (large file transfers, etc.). Both are connected to monitors, which happen to be a matching pair.

Both machines are connected to a Gigabit switch using CAT6 cable, which is important as you’ll see later. Note that the rest of my office’s network runs 100BASE-T, not Gigabit, but the switch allows network traffic between my machines to move at full Gigabit speed.

The software setup

I only need the XP machine occasionally, and it was killing me to have that second monitor sitting there without being able to use it with my Mac. I already had Synergy set up on both the Mac and Windows machines so that I could seamlessly move the mouse and keyboard input between the two machines. I use QSynergy on both machines – I found it easier to configure than the alternatives I’d tried.

It occurred to me that if I could already control the Windows machine with the keyboard and mouse connected to my Mac, I only needed to be able to display a second screen from my Mac on the Windows machine’s display. There had to be software that would allow me to do that, right?

As it turns out, there is. ScreenRecycler is a program that creates a virtual display on your machine, then serves it up as a VNC remote display. Now, if you’ve ever used VNC before you know that it can be fairly slow, even on a local network.

In my experience VNC speed is a function of two primary factors: the network speed, and the VNC client. I tried a number of different VNC clients on the Windows computer including the ones suggested for Windows by ScreenRecycler: TightVNC and VNC Navigator. I was never able to get TightVNC working well, but VNC Navigator works.

Usage

What I really enjoy about this setup is it means that I can use my Mac laptop as if it has two external displays, and with the press of a hotkey combination I can drop into Windows hiding underneath the second screen. I typically leave my Mac closed and run in “clamshell mode” using only the external monitors, but if I have on occasion also used the MacBook Pro’s display, and it seems to be able to drive three displays with no issues — the built-in at 1440×960, and two externals at 1680×1048.

Real-world results

While ScreenRecycler bills itself as being fast enough to run video on the second screen, it’s not quite fast enough for that on my setup. It is, however, fast enough to use almost any productivity software and not feel like there’s a lag. I tend to leave my OmniFocus and iTunes windows open on the second monitor, but also regularly use it for comparing documents.

While this may not seem like the most minimal of setups, it’s actually a very efficient way to use two monitors and one keyboard & mouse. I’m able to hide the laptop away under my desk with the desktop while still being able to take advantage of multiple monitors, and have access to the Windows computer without taking my hands off the keyboard.

If you have a spare Windows or Mac computer handy, ScreenRecycler at $29.90 USD is an affordable option to drive extra monitors from your Mac, as compared to buying a USB display adaptor.