Multiplicity: Control Two Computers With Your Mouse And Keyboard

If you’re anything like me, you’ll be quite used to working with more than one computer at the same time. I’m frequently using my main PC to copy encode video, while using my older machine get on with other things like surfing the web and writing – sometimes, my laptop even gets in on the mix!

Working with two or more computers simultaneously is great, but it does mean that you need a large desk to accommodate the two keyboards and two mice. You could install a KVM switch that lets you use one keyboard and mouse to control two computers, but if you’re looking for a free solution, Multiplicity could be the tool for you.

There are two different versions of this handy utility available – one is free and one is paid for. The version that costs money can be used to control up to nine computers with a single mouse and keyboard, but for most people, the free version’s limit of two machine should be sufficient.

Getting Installed

The thing to bear in mind about Multiplicity is that you will need to install it on both of the computers you intend to use. One is the referred to as the Primary computer – this is the one whose keyboard will be used to control both machines – and the other is the Secondary. Start by installing the software on your Primary machine.

You can download a free copy of Multiplicity by paying a visit to the program web site and clicking the ‘Get it Now’ button. In the Multiplicity (free) column, click the Download button. Enter your email address, click the Download button and you’ll be sent a download link – download the file and double click it to start the installer.

There are two versions of Multiplicity available, and the free edition is powerful enough.

There are two versions of Multiplicity available, and the free edition is powerful enough.

The installation is a very standard one, but you might want to watch out for the attempted installation of the AVG Security Toolbar. At the end of the installation, click the ‘Be a Primary computer’ button.

Be sure to choose the computer whose keyboard you want to use to be the primary machine.

Be sure to choose the computer whose keyboard you want to use to be the primary machine.

Once you have the software installed on your Primary machine, turn your attention to your Secondary computer – you should use the download link in the same email to grab a second copy of the installer, or you could copy it from one machine to the other over your network. Run through the installation again, this time choosing the option to set up a secondary computer.

Getting Connected

On your Primary computer, you may find that a scan for secondary machines starts automatically – if this is not the case, just click the ‘Add computer’ button to the right of the program window. Should you find that your secondary computer is not automatically detected, enter the name of it before click the Add button – you can check the screen of your secondary computer if you do not know the name of it. You should find, however, that you can just click the icon representing your secondary computer before clicking the Add button.

A manual option for adding machines is available if the automatic scan does not work.

A manual option for adding machines is available if the automatic scan does not work.

As a security measure you are required to provide a password before one computer will be able to control the other. Check the screen of your secondary computer and enter the passcode displayed on the screen into the relevant field on your primary machine. Click the Save button and you’re ready to continue.

Connections are protection by passwords to prevent unauthorized control of your computer.

Connections are protection by passwords to prevent unauthorized control of your computer.

Sharing Your Keyboard And Mouse

For basic usage there is very little additional configuration that needs to be done. That said, you will need to let Multiplicity know just how you have your computers arranged so you can move your mouse cursor from one screen to another in a way that makes sense. You’re presented with a 3×3 grid, at the center of which you’ll see your primary computer. You can drag and drop the icon representing your secondary computer to any of the remaining eight squares depending on its position on your desk.

You can use the settings screen to configure how your computer are positioned.

You can use the settings screen to configure how your computer are positioned.

My main computer sites pretty much in the center of my desk and I’ve placed my laptop to the left of it. As such, I’ve adjusted the position of the computer icons accordingly. With positioning correctly configured, you can move the mouse cursor off the edge of the screen of your primary computer and it will re-appear on the screen of your secondary machine.

This works very much like using a dual monitor computer, but in this case each monitor is displaying the output from a different machine. Whichever computer screen shows the mouse cursor is the computer you are controlling and this is the computer that can also be controlled by your primary computer’s keyboard.

Extra Settings

For the most part you should find that Multiplicity just works, but there are a couple of interesting settings that you might want to investigate. On your Primary computer, move to the Settings tab of the Multiplicity window you can use the three drop down menu to choose keyboard shortcuts that enable you to quickly switch between computers without the need to scroll to the edge of your screen.

Switch more quickly between computer using keyboard shortcuts.

Switch more quickly between computer using keyboard shortcuts.

Click the button labelled ‘Control switching based on mouse movement’ and there are two more useful settings. Tick the box labelled ‘Mouse should wrap around the grid’ and you can move your cursor indefinitely in one direction – keep it moving left and it will just wrap around from one monitor to the other without stopping.

Mouse wrapping is a handy option available in Multiplicity.

Mouse wrapping is a handy option available in Multiplicity.

The other handy setting is ‘Unless shift is held down. This is fairly self-explanatory, but with the option activated your mouse cursor will remain locked to the current computer’s screen unless your press Shift in which case you will be able to move from one screen to the other – useful if you’re using an app that has buttons right at the edge of the screen.

I find that Multiplicity is a great alternative to a KVM switch. Have you found any other tools that are equally useful? Share your thoughts in the comments below.


  • Predrag Krstic

    I’m using Synergy ( http://synergy-foss.org/ ), it’s open source tool, with very good support for different platforms (Win, OSX, Linux). What I like is how Synergy handles multi monitor server (treat them as one big monitor).

    • Predrag Krstic

      Forgot to write, what I miss in this kind of applications is shared clipboard, maybe it exists in some commercial app, but those free apps doesn’t support this (at least text). It would be very useful if I could transfer for example user name and password from one computer to another, especially in multiplatform environments (in my case MacBook Pro as dev machine and Win7 as test machine).

      • Yanick

        May be you could use PhraseExpress (http://www.phraseexpress.com/) with the network option?

        I use only the workstation freeware option and it’s a very powerfull little thing. I know there is a network possibility, but never tried it…

  • Yanick

    Is there any similar software that would allow me to also view the screen of the other computer? So end up with one noisy server in the basement and remotely control it from the office on the second floor? (screen + keyboard + mouse sharing?)

    Thanks!

    • Dustin

      I use teamviewer to remotely access my desktop when im away from home. Its free and works great! Maybe it can help your situation or get you started on the right path.

      http://www.teamviewer.com/en/index.aspx

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