What Are KVM extenders?
KVM extenders are devices specifically designed to increase the distance that a keyboard, monitor and mouse (KVM station) can be placed from a computer or KVM switch. Some KVM extenders can also extend the connection from a computer to audio and serial devices or even USB peripherals including security hardware, drives and printers.
KVM extenders have been available for the last 15 years or so and were introduced to overcome the distance dependent bandwidth limitations of traditional VGA cable and the distance limitations of the PS/2 protocol.
High resolution computer graphics and long distance VGA cable's
The VGA (Video Graphics Array) connector is by far the most common interface used to connect a monitor to a computer. The VGA standard originally supported a resolution of 640x480 and it is possible to extend VGA up to a distance of 150 meters or more over good quality VGA cable. However, high quality VGA cable is dual shielded and contains mini coax cores to carry the colour signals. This makes the cable thick, stiff and difficult to terminate and therefore a poor choice for long distance cable runs. Also, modern computer graphics cards still utilise the VGA connector and cable, but now resolutions of 1920x1200 are not uncommon. These high resolution computer graphics do not transmit well over long distances of VGA cable as the high frequency signal components are attenuated causing severe degradation to the resulting image.
PS/2 keyboard and mouse protocol
In addition to this, the PS/2 keyboard and mouse protocol is only designed to run to a distance of about 10m, so longer keyboard and mouse cables do not work with all peripherals. This combination of factors means that the VGA and PS/2 protocols must be modified in some way for successful long distance transmission, and this is what KVM extenders are for.