Computer Servers are available in compact 1U/2U rack-mount configurations, these days. So, one can place multiple servers in a single rack which can save a lot of space in a server room/ data center.
Since computer servers are similar to normal computers and each of them run different applications, each server requires a keyboard, mouse and monitor/ video terminal. At the same time, people do not sit and work on the servers all the time, unlike how they do with computers. Most of the servers are on an auto-run mode but they do require display, data input/output occasionally.
So, it is actually a good idea to share a single keyboard, mouse and monitor for multiple servers as,
1. They are used occasionally.
2.One set of keyboard, mouse and monitor for each server occupies a lot of space, which is a premium in data centers.
3.The cost of buying separate monitor for each server can be quite high.
That's exactly the reason why we have KVM Switches – To share a single set of keyboard, mouse and display terminal (monitor) across multiple servers.
Every KVM Switch has connections to connect with the keyboard/ mouse ports of each server using USB interface or PS/2 interface or both. It also connects to the monitor port of each server using VGA interface. So, now we have many servers at one side whose keyboard, mouse and monitor ports are connected directly to the KVM Switch.
On the other side, we have the control terminal that consists of a single set of keyboard, mouse and monitor that connects to the KVM Switch as well. They can connect using USB interface, PS/2 interface or both. Using this one set, it is possible to select which server we want to control/ access via the KVM Switch.
A user can select which server they want to work with, by using a toggle switch provided on the KVM Switch or by using keyboard short-cuts from the control terminal or by using a menu driven on-screen display from the control terminal.
In most cases, the KVM switch itself is rack-mountable and a separate pull-out tray is available with some rack vendors that can accommodate the keyboard, mouse and an LCD monitor within the rack itself.
When all the servers and the monitoring terminals are connected in this way, one can just start working because the entire set-up is plug and play. So, there is no need to install device drivers or any other software on the servers/ KVM switches.
There are multiple KVM switch models available based on the number of servers/ computers they can control/ communicate with. Commonly available models are 2-Port KVM Switch, 4-Port KVM Switch, 8-Port KVM Switch, 16-Port KVM Switch, etc.
KVM Switches generally support servers/ computers running on multiple operating systems like Windows, Linux, Mac OSX, etc. Some KVM Switches can even emulate keyboard/ mouse/ video terminals on all the connected servers, so that there would not be a 'no-input/output device attached' error, if and when they re-boot (during power-cuts, for example).
Many KVM Switches can be cascaded together (using special cables) in order to increase the number of servers that can be controlled using a single control terminal (keyboard, mouse, monitor).
The KVM Switch network is a proprietary network and there is no interference with other LAN traffic,etc. Most of the KVM Switches support a bandwidth of 200 MHz or higher and a resolution of up to 1920 x 1440, which is sufficient to support HD Video output.
KVM Switches come with all the cables needed to attach to the individual server keyboard, mouse and video (display terminal) interface ports.
Common KVM Switches are available in the following configurations.
•16 Port USB & PS/2 COMBO KVM switch
•8 Port USB & PS/2 COMBO KVM switch
•4 Port USB & PS/2 COMBO KVM switch
•2 Port USB & PS/2 COMBO KVM switch
•8 Port USB & PS/2 COMBO KVM switch with remote control
•4 Port Auto USB KVM switch
•2 Port Auto USB KVM switch
•4 Port PS/2 KVM switch
•2 Port PS/2 KVM switch