KVM Switch Boxes

A KVM switch (with KVM being an initialism for Keyboard, Video, Mouse) is a hardware device that allows a user to control multiple computers from a single keyboard, video monitor and mouse. more...

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Although multiple computers are connected to the KVM, typically a smaller number of computers can be controlled at any given time. This is referred to as the 'Blocking Factor'. Modern devices have also added the ability to share USB devices and speakers with multiple computers.

Use

A user connects a monitor, keyboard, and mouse to the KVM device, then uses special cables to connect the KVM device to the computers. Control is switched from one computer to another by the use of buttons on the KVM device, with the KVM passing the signals between the computers and the keyboard, mouse and monitor depending on which computer is currently selected. Most devices also allow control to be switched through keyboard commands (such as hitting a certain key, often Scroll Lock, rapidly two or three times). Some KVM devices also provide peripheral emulation - they send signals to the computers that are not currently selected to ensure that they do not think that the keyboard, mouse and monitor are disconnected.

Devices differ in the number of computers that can be connected, with anywhere from two up to 64 computers possible. Enterprise-grade devices can also be daisy-chained to allow even greater numbers of computers to be controlled from a single set of a keyboard, video and mouse.

A KVM switch is useful where there are multiple computers, but no need for a dedicated keyboard, monitor and mouse for each one. They are frequently used in data centers where multiple servers are placed in a single rack with a single keyboard, monitor and mouse. A KVM switch then allows data center personnel to connect to any server in the rack.

Software alternatives

There are software alternatives to a hardware KVM switch such as Synergy, Kavoom!, Virtual Network Computing (VNC), teleport or the non-free Multiplicity and PC Anywhere, which do the switching in software and forward input over standard network connections. This has the advantage of reducing the number of wires needed, and the screen-edge switching it provides makes it easier to forget that you are using two computers. However, there are some disadvantages. Software alternatives typically require additional software to be pre-loaded onto each one of the target servers or computers to allow clients to remotely attach to. They also can not be used when the host Operating System is not installed yet or has not started: operating system installations are thus not possible nor is access to a computer's BIOS or other built-in configuration areas. Finally, the software alternatives can be difficult or impossible to access if the computer is very busy or has stopped responding to network connections.

Read more at Wikipedia.org