Here at my office, we have five servers that are controlled by a single mouse and keyboard and are connected to only one monitor for ease of administration and lack of extra space! If you have more than one desktop at home, maybe a Windows box and a test box with installed, you can connect both to one monitor using what is called a KVM switch.
A KVM switch, which shockingly stands for Keyboard, Video, Mouse, is a small piece of hardware that looks kind of like your wireless router, but instead of network ports, it has a VGA video port and PS2 or USB mouse/keyboard ports. The device is very simple to use and usually requires no external power source! Most KVM switches will draw their power from the computers that are connected through the provided cables.
Here’s an example of a D-Link 4-port KVM switch. One each side there are two sets of mouse, keyboard, and video connections. At the top left, you’ll notice a small button, which is used to “switch” between the computers. A lot of the newer KVM switches also allow control to be switched by pressing a particular key or performing a set of keystrokes on the keyboard.
There are two types of switches that you can buy, USB or PS2. Now that many computers have USB ports, the KVM cable will have one end that is USB, which you can simply plug into any free port and it will control both the mouse and keyboard. However, I suggest buying a PS2 KVM switch (like the D-Link shown above) because I have learned form experience that if something goes wrong with your computer and you have to boot into safe mode or do something in the BIOS, the keyboard and mouse will not work if connected to a USB KVM switch!
You can purchase KVM Switches that support anywhere from two computers all the way up to 64. Of course, these types of switches were mostly meant for large server rooms at companies, but now that many consumers have more than one desktop at home, D-Link, Netgear, and other hardware manufacturers have started creating consumer versions with two or four ports.
Most KVM switches that you will find online will have cables that are only about 6 ft. long, which means that the computers have to be in close proximity of the switch. If you want to connect multiple computers that are more than 10 ft away from the central monitor, you can use either a local remote KVM device or KVM Over IP.
With a local remote KVM device, you can connect computers to the device using normal network Category 5 cables. This setup require small interface devices at the computers that convert the peripheral device signals to network protocols that can be transmitted over Cat 5 cables and then get converted back to analog signals at the KVM device.
However, this option still requires that cables (Cat 5 in this case) are used to connect the computer directly to the switch. If you want to be able to control any computer on a network, you can do so using a KVM IP switch. This means that the computers can be connected to Local Area Network, Wide Area Network, or through a phone-line. The signals are converted and sent over the network to the KVM device where they are converted to normal signals.
You can find these more advanced switches at more specialized online stores, such as KVMs.com. Enjoy!
Thanks to :- http://www.online-tech-tips.com/computer-tips/how-to-connect-two-or-more-computers-to-one-monitor/