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How to use an old Mac laptop as a passable external display for a new one

This is a quick one. The executive summary:

New Mac + ScreenRecycler + IP over Firewire = Passable external display

(no need to give up your main machine's precious ethernet connection)

Why? Well, I've got an old Mac laptop, which isn't too much use by itself (PB 1Ghz with 768mb of RAM against a Dual 2.1Ghz MacBook with 3Gb). But, it is an extra display. In fact, I've always thought it a shame that laptops and systems with permanent displays don't come with a video bypass, so that when the machine itself is past its useful lifetime, the display can still be used. This is a less power-efficient option to that end.

How? First, purchase a license to ScreenRecycler, a tool that basically lets you use any machine you can run VNC on as an external display for a Mac (via a virtual display driver). It currently costs $25... which seems pretty decent for getting an extra display. But, because it uses the network to connect the two machines, you want that connection to be as fast as possible. While you can trivially use an Ethernet cable (Macs have, for a long time, done auto-crossover, so any ethernet cable will do just fine), I want to keep my Ethernet port, because Ethernet is precious where I go to school, and also more reliable.

How can you connect the two machines, assuming you don't have access to an appropriate ethernet switch? Firewire! If you're not using your firewire ports for anything else, just enable "Built-in Firewire" in your Network preferences pane of each Mac. In fact, if you then turn on Internet connection sharing in the Sharing preference pane (share your Built-in ethernet to your Built-in Firewire, naturally), the "screen" machine will even be able to connect to the network. I use this so that I can run Foldershare on both machines, and have a constant backup of several folders on my main machine.

The final step is to plug the firewire cable in between machines, install ScreenRecycler, and start up the screen sharing. I used the JollysFastVNC that ScreenRecycler includes with it, and have it set up with the name of my primary machine and the settings for auto-reconnect and fullscreen turned on... I just have to wake the extra machine up from sleep, and it returns to being the 'extra' screen as soon as it has found the network connection. I further use a tool called MarcoPolo to detect when I'm sitting in this configuration and launch both ScreenRecycler as well as changing the Network Location to the one where I have this network setup enabled.

Simple enough? No screenshots, 'cause I figure this is still a fairly advanced tutorial. If you have trouble following my steps, post a comment, and I'll beef things up.

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ScreenRecycler can also use a Windows machine as a second monitor.

If you want to spread a Windows desktop across computers, MaxiVista does that. This comment thread points to some more options.

DMX does the same for Linux. ShareKMC is mentioned as a free program for Windows, but I couldn't find it to download.

If you don't need to spread the desktop out but just want to control a bunch of computers with one mouse/keyboard (i.e. network KV switch) then try Synergy .

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