What is a KVM Switch?

A KVM Switch allows the connection of a Keyboard, VDU (Video Display Unit) and mouse to multiple computers. The user determines which one of a number of computers they would like to take control of. It is a hardware device that allows selection of individual computers or servers by means of a simple control system using a simple dial or button.
Some KVM Switches can have the added capability to control associated USB devices and even speakers. Products utilising Category 5 twisted pair cable can be used to control equipment at distances up to 300 metres, often using some form of manufacturers proprietary protocols.
A later innovation has been KVM over IP, where the KVM Switch conveys the control information and captured keyboard, video and mouse signals via an IP over Ethernet link to a remote application. This greatly increases the range and scope of control over LAN, WAN and Serial Point-to-Point links. The common method is to connect via a web browser using some form of proprietary software, but security is an obvious issued. This is dealt with by implementing SSL (Secure Sockets Layer) with 128-bit encryption.
Organisations that have a number of dedicated servers may well opt to use KVM Switches to enable the servers to be monitored and controlled individually from a single device. Administrators and operators can switch between physical server devices at the flick of a switch or push of a button.
Keyboard, Video and Mouse Switches come in various formats including Desktop and Rackmounted models. These products come as Direct Connect systems, Networked systems and those that are controlled from a dedicated console. In addition to the KVM Switches most major manufacturers will normally have an extensive range of accessories such as interface modules, cable adapters and cable kits.
For some time now, VGA based switches have probably been the most popular format, but HDMI (High-Definition Multimedia Interface) and DVI (Digital Visual Interface) are quickly becoming efficient digital alternatives to VGA.
DVI is a common digital standard that is popular for PC connections to display units and HDMI is an uncompressed digital standard for audio and video signals. It is able to pass both the video and audio down a single cable between such devices as DVD Players, Set-Top boxes and a digital television.
Control connections on KVM switches are commonly PS/2, which was the common standard for mouse and keyboard connections for many years, and USB which is simpler and more flexible. A lot of Switches have the option of either. The user just has to remember to purchase the right cable types, unless they are supplied with the switch.
KVM Switches are manufactured by a large number of manufacturers. If you are looking to purchase then I recommend the manufacturer that has a good reputation for providing an extensive range of accessories and a good range of switches themselves.


David Christie is MD at NSTUK Ltd, a Technical Training and Consultancy company based in the Northeast of England. David delivers technical training in the area of Data Communications and Telecoms and also provides consultancy and Training Needs Analysis. The company runs an ecommerce website specialising in the sale of Networking hardware and consumer electronics. Website: http://www.ipexpress.co.uk
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