First of all, let's explain those initials KVM. They stand for Keyboard, Video and Mouse. Those are the three peripherals every computer needs to make an operations console.
The simplest arrangement is a KVM switch which is a device about the size of a modem. You plug your keyboard, monitor video and mouse into the KVM switch instead of a computer. Then you run a set of KVM cables from the switch to each computer you want to control. A 2 port KVM switch controls 2 computers. You can also get 4 port and 8 port KVM switches in a desktop size.
How do you work KVM? You can push a button on the KVM switch to move from computer to computer. Or, there are keyboard shortcuts you can use to make the switch back and forth. Another mode automatically switches the monitor between computers every few seconds so you can keep an eye on what's going on. That's especially useful for monitoring a group of servers that you expect to run automatically. If you need to intervene to fix a problem or install new software, simply select that particular server on your KVM switch.
This simple type of KVM switch will work up to about 50 feet away from the computers you are controlling, so it is generally used in a server room or office environment. If you want to get farther away, you'll need to install a Cat5 KVM switch or a Cat5 KVM extender. These use Cat5 computer wiring instead of the short bundles of keyboard, video coax and mouse wires. With a Cat5 KVM switch you can move your control point hundreds of feet from the server room. Some of these switches are stackable so that you can add KVM switches to control dozens or hundreds of machines from one console. A matrix KVM switch lets you have multiple consoles to let several operators have access to any desired server or PC.
KVM switches and Cat5 KVM switches are analog devices. The signals are analog control signals that use their own wiring network between devices. This is also called out-of-band KVM control. In-band systems work over the company LAN, much like the way VoIP telephones and computers share a common LAN network.
Digital KVM uses IP transmission for in-band operation. These are the newest and most sophisticated KVM switches. With IP networking built-in, there is no distance limitation. You can sit in your office in Chicago and control a data center in Asia if you wish. Or set up a "virtual data center" with servers in scattered locations. It's all the same when you are accessing them over the Internet.
That brings up a good point about security. Remote KVM solutions need security features such as encrypted transmissions. This is typically built into the system, essentially creating a virtual private network specific to your KVM over IP system.
Small KVM switches like those made by Belkin can be purchased at office supply stores for control of 2 to 4 computers. Larger Cat5 KVM switches and digital KVM systems are sold by companies such as Raritan, Avocent, and Rose.
IP bandwidth including virtual private networking is available through T1 Rex.
