KVM Basics

Share a keyboard, monitor and mouse

KVM basics

There are a wide variety of KVM switches that meet a wide range of needs, from complex switches that allow you to control 16 or more computers in server rooms to simple ones that control two computers in home networks. Of course, prices vary as well, from thousands of dollars to $50 or less.

Despite the differences, all KVM switches share the same basic concepts. As we mentioned earlier, you connect a keyboard, video monitor and mouse to the KVM, and then use special cables to connect each computer to be controlled to the KVM switch. You use some method to switch between the computers being controlled, switching from computer to computer...using a single keyboard, monitor and mouse.

Here are some things to keep in mind as you decide which KVM switch might be right for you:

Obviously, the primary decision is how many computers you'll want to control. Many computer users may want to pick an inexpensive model that will control only two computers, a so-called 2-port model. However, as soon as they decide to add a third computer, the 2-port KVM switch becomes worthless and they'll have to replace it with a 4-port or even 8-port model. We suggest home users consider a 4-port model to control two computers with room to grow for an added laptop or other computer.
Control method. Some models allow you to control the KVM switch from the keyboard using "hot key" commands, a combination of keys pressed at the same time or in sequence. Others, provide simple push buttons on the switch itself to change the computer being controlled. Still others provide both types of control methods.
Display. Likewise there are different methods to display which computer is currently being controlled. Inexpensive models will have a simple LED on the KVM switch to indicate which computer is currently being controlled. More expensive models have on-screen displays that will indicate the computer being controlled directly on the monitor.
Resolution. One of the key things to look for when purchasing a KVM switch is the resolution capability. Many computer users have graphics cards and monitors that will display very high resolutions and very high frequencies. Resolution relates to how precise the image is (indicated by pixels or dots per inch) and common resolutions are 1024x768, 1280x1024 or even higher. Frequency relates to how often the screen is drawn and frequencies below 60 Hertz can result in screen flicker on regular computer monitors. Since the video signal must pass through KVM switches, they differ in their ability to handle the resolutions and frequencies. Thus, the image shown on the monitor can actually be degraded by the KVM switch. The key is to look at the specifications for KVM switches and make sure that the models being considered can handle at least the resolution and frequency currently being used. Even higher is better since it gives "head room" for the future.
Cables. All KVM switches use special cables, but some are more custom than others. Some models, particularly those aimed at professional users such as Raritan KVM switches, use custom cables that only work with those models. Other models use cables that are "universal" KVM cables and will work with several makes and models of KVM switches.
Ports. Closely related to cables are the types of ports that the KVM switch uses. Today, most switches use PS/2 connectors for the keyboard and mouse, but you can still find some that have the old, larger keyboard connector (or include adapters) and serial ports for old-style mice. The latest switches use USB connectors which add a number of advantages as I'll discuss on the next page review of the Belkin switch. Still others have a combination of PS/2 and USB connectors, allowing flexibility.
Configuration. There are numerous configurations for KVM switches, but most fall into three main categories. The most inexpensive switches are small boxes designed to sit on or under the desk and have ports for the cables or the cables permanently attached. They do not have buttons but instead are controlled by a combination of keystrokes on the keyboard. (Here's an example of this configuration, again from Belkin). The most common configuration is a larger box that sits on the desktop and has buttons on the front used for switching between computers. On the back of the box are the ports for the cables. (Here's an example of that type.) Finally, there are some unique configurations such as the Belkin model that we review on the next page.
Special features. As you'll see on the next page, some KVM switches have special features such as built-in cable management, switching of audio and microphones, automatic switching (timed switch from computer to computer). Make sure you review lots of switches to find the special features you want.

If you want additional help on sorting out all of the options and deciding which KVM will work for you, you might want to try the KVM selection wizards at the Belkin site or KVMswitches.com.

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This page last updated 02/03/2003