If your desk is home to more than one computer, reaching for separate peripherals each time you switch between them is a real hassle. Most desks don't have room for multiple keyboards and mice, and it's much more convenient to use one set of peripherals to control all your computers.

Traditionally, that meant investing in some hardware (a KVM switch), but these days, you can do it for free using software. Here we'll show you how to install and configure Synergy.

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The program lets you move the mouse pointer to the side of one computer’s display and across onto the other’s, just as if it was a secondary monitor. This means you will need a separate monitor for each computer, unlike a hardware KVM, and the computers merely need to be connected to the same network.

Synergy sends your mouse movements and keyboard presses to that computer, as if the peripherals were attached to it directly. It works with any number of computers, either laptops or desktops, and there’s a client for Linux and Mac OS X as well as Windows. It even lets you copy text from a Mac, and paste it into a document on a PC, which can be a fantastic time-saver for some people.

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As long as you have a fast Wi-Fi network or use Ethernet cables, there’s no lag at all when moving the mouse or typing.

Synergy can be fiddly to set up, though. In addition to installing the software, you’ll need to assign a static IP address to the computer with the peripherals physically attached to it, which will be designated the Master. This is because Synergy needs an open port in your router’s firewall to communicate.

The exact process depends on which router you have. Virtually all routers let you assign fixed IP addresses. We’ll demonstrate how to do it on a Thompson TG585 router, but the same principles apply to all brands.

The final job is to assign screen names to the other computers, so Synergy knows which screen is on the left, and which is on the right.

If it sounds complicated, it really isn't. The only tricky aspect is configuring your network correctly, which we’ve covered in the box to the right.

Once Synergy is up and running, you’ll wonder how you managed multiple computers without it.

How to set up and configure Synergy

1 Go to Synergy's website and click the Download link. Either make a donation or click Continue. Download the correct installer for your operating system. Choose 32-bit if you aren’t sure which version of Windows you have.

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2 Run the file you just downloaded. Agree to the terms and conditions, then click next to install the software. You’ll need to download and install the appropriate version of the Synergy software on each computer you intend to use with your shared mouse and keyboard.

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3 Log in to your router via your web browser. Look for a page which lists all the devices connected to the router. Identify your 'Master' computer, and ensure its IP address is set to be static rather than dynamic, with a value such as See How to assign a static IP address for more details

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4 Still within the router’s interface, another option will allow you to open ports for certain applications. Synergy uses 24800 by default, so follow your router's manual or online help to open this port, enabling both TCP and UDP protocols for this port and ensure it is applied to your Master computer (usually you select it from a list or enter its IP address). Save the changes.

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5 On the Master computer, launch Synergy, then tick the box labelled Server. Click Configure Server. For each client, drag the monitor icon from the top right into the main window and arrange monitors in the order in which they’re positioned on your desk. Double click each icon, then give it a unique screen name. Click OK, then click Start.

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6 On each client computer, open the Synergy application, and go to the settings and ensure it has the same screen name you chose in the last step. Tick the box next to Client. Enter your master computer’s IP address. Then click Start. If all is well, it should say ‘connected to server’ and you can move your mouse between your computers and use the keyboard to type.

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