A KM switch lets you control multiple computers using a single keyboard and mouse. This differs from the more popular KVM switch in that you still require separate monitors for each computer. If you have multiple desktop machines, that saves on desktop real estate since you don't need to have more than one keyboard and mouse. And if you are using a laptop and desktop together, these devices save you the hassle of having to switch to the other keyboard. And when gaming sometimes, every second counts!
You can go out and buy a lovely hardware KM switch like this:
... but nowadays, there are plenty of software equivalents.
The way the software KM switches work is when you move your mouse offscreen (in any direction, up or down, but more commonly, left or right), control moves to another computer. This means that the OTHER computer will start receiving your mouse and keyboard input.
My setup at home has three computers: two desktops, and a laptop for work. The center computer is my primary computer and the keyboard and mouse is physically attached to that machine via the standard USB ports. When I move the mouse to the left, it appears on my other desktop machine. If I move it to the right, it appears on the laptop I use for work.
KM switches are really great for gaming. You can use it to dual box (to control characters running on two separate computers). You can look things up on the Internet on the secondary computers while playing fullscreen on your primary machine.
I use a program called Multiplicity which works pretty well. It does have some drawbacks: some games like Vanguard: Saga of Heroes, City of Heroes, and Warhammer Online stop responding to mouse clicks after you've switched off and on screen a few times. Its rather frustrating since Warhammer Online is one of the main games I play right now. It also confuses programs that use mouselook when your mouse ends up "offscreen," so I disable it when running a game from the first person perspective like Fallout 3. Multiplicity has a number of really great features though:
- You can share clipboard information between the machines. This means I can look up coordinates in eq2wikia and paste them into my fullscreen EQ2 instance running on my other computer. With as much running around and exploring that EverQuest II quests typically require, that's a lifesaver!
- You can also share FILES between machines. Its as easy as highlighting the files in Explorer, hitting Ctrl+C (the keyboard shortcut to Copy), and then moving the mouse "offscreen," and then hitting Ctrl+V (the keyboard shortcut to Paste) in the other computers folder.
For a more general purpose KM switch that won't cost a dime, check out Synergy. It supports Mac, PC, and Linux, so multi-OS users would benefit from that. I haven't used it myself yet, but Stargrace seems to like it. I intend on trying it out because of the frustration I have with Multiplicity not working with Warhammer Online.
If you are primarily a World of Warcraft player, you might instead look into Octopus or Interbox, since these appear to be customized particularly for boxing in WoW. They support some features such as key cloning (so you can have some keyboard commands that get broadcast to all clients simultaneously.) It can also broadcasting multiple clicks to multiple windows on the same machine.
Did you hear about the guy who plays 36 World of Warcraft characters at the same time? He uses Octopus.
Of course, if you just want to broadcast multiple clicks but don't want a KM switch, you can use Keyclone. This software will even work with multiple instances on the same machine.
One commercial alternative that I have tried is Exxtramon from KaVoom software. This program is pretty neat because in addition to letting you control two machines with a keyboard and mouse, you can also use your secondary computer's monitor as an extension of your primary computer's desktop. Let's say you have a laptop and a desktop. In that case, the software would make your laptop behave as if it was a second monitor attached to your desktop. However, your laptop can still do its own processing and run its own programs, and you can then flip back and forth between the extended "virtual desktop" and the laptop's actual desktop at will. Its a neat feature but not something I needed for gaming. However, they do offer a separate product that is only a KM switch without the virtual desktop feature.
Anyway, hopefully this helps anyone out there interested in dual boxing, or struggling with dual boxing without these tools. Even if you are not dual boxing, if you have more than one computer side by side, a software KM switch will seriously make your life easier.