How to Connect Two or More Computers to One Monitor

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 Linux installed, you can connect both computers to one monitor in three different ways: using the additional ports on the back of your monitor, using what is called a hardware KVM switch and using a software KVM switch

Additional Ports

The easiest way to connect multiple computers to one monitor is to first check the back of your monitor to see how many inputs there are. On my monitor, I have an HDMI port, a DVI port and one VGA port. That means I can connect up to three different computers to my one monitor.

ports monitor

Obviously, there are downsides to this approach because HDMI can carry the highest resolution with the most stability. DVI and VGA can also carry HD signals, but problems can start to occur at higher resolutions that require greater bandwidth. VGA also uses an analog signal as compared to a digital signal used by HDMI and DVI, but you probably won’t be able to tell the difference at lower resolutions.

Hardware KVM

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 VGA or HDMI video ports 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.

kvm local remote

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.

kvm over ip

You can find these more advanced switches at more specialized online stores, such as KVMs.com. The only issue with these more advanced KVM solutions is that they can get pretty expensive. What if there was a cheaper way? The software KVM is a possible solution.

Software KVM

Synergy is a piece of free software that basically acts as a software KVM and lets you control multiple computers via a main “server” computer. Using this software, the computers still have to be next to each other in order to use it. The other thing it does not help you with is reducing the number of monitors. With a hardware KVM switch, you can use one monitor with multiple computers, but with Synergy you can use one keyboard and mouse on multiple computers. It basically just saves your from having to buy a bunch of hardware and having to use a lot of cables just to use the same mouse and keyboard on multiple computers.

synergy

So now that you know the limitations of the software, it’s still a good solution if you have three separate computers running close to each other and you just want to be able to control all of them with one mouse and keyboard. The other great thing about the software is that it runs on Mac, Linux and Windows and allows you to share your clipboard between all the computers. You can also simply drag and drop files between computers as you move your mouse between them.

Synergy is also good if you were planning on installing VNC software to remotely control another computer. Now you can just move your mouse to the other computers’ screen and start working on it. Obviously, like mentioned above, the computers all have to be close to each other. With VNC, you can remotely control a computer in another room without needing to see the computer.

Hopefully, one of the three methods mentioned above will help you in controlling more than one computer from a single monitor. If you have any questions about your setup or what kind of KVM switch to buy, post a comment and I’ll try to help. Enjoy!

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