Computing environments such as server rooms often have so many PCs in such close proximity that having a separate display, keyboard, and mouse for each is not only confusing, but a waste of space. You can of course stick with one of each, then attach them as necessary, but that's another time suck. A better solution is a KVM (Keyboard. Video, and Mouse) switch, or if you're cable- and cost-averse, KVM software such as Multiplicity 3.
A physical KVM switch has inputs for a keyboard, mouse, and display and sets of outputs for the same to drive multiple PCs. You run cables to said PCs then toggle between them using switches, a rotary dial, etc. With Multiplicity, you can forego the cables, instead utilizing one PC as the KVM switch (the primary PC in Multiplicity-speak) and your local network as the cabling to transmit signals to and from secondary PCs. Basically, it's remote control software done up to emulate a KVM switch.
Setting up Multiplicity is simple. Install it on each participating PC, defining one as the primary (controlling) and the rest as secondary. When you define a PC as secondary, you're provided with a pass code that you enter on the primary PC to establish contact.
After you've installed Multiplicity on all the PCs, there are two ways you can pass input to the secondary PCs. The first is seamless mode for secondary PCs that have their own display. Simply add the secondary PC to the seamless matrix (3x3 up to 7x7) and when you mouse off the edge of the primary PC's display, mouse and keyboard control pass automatically to the secondary PC situated in the matrix that borders. It's exactly like a multiple-monitor setup where the mouse travels from one screen to the next, except that each screen belongs to a different PC.
Scenarios where seamless mode is useful include environments where separate PCs are tracking different stock markets or displaying separate surveillance cameras, as well as multiple displays monitoring the health and activity of the PCs they're attached to.
The second method is full KVM mode, which is exactly like using remote control software. Right-click on the Multiplicity icon in the system tray, select KVM mode, and select the PC you want to control from the list. You can KVM a secondary 'PC' full-screen (default) or displayed in a window.
Multiplicity will also pipe audio from a secondary PC to the primary PC or vice versa, which can be handy. Version 3 also adds the ability to drag and drop files between the PCs in the matrix. That's all nice, but I do have a couple of gripes.
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