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What is KVM?

Posted by Jess Wu on

KVM is an acronym for Keyboard, Video (monitor) and Mouse, which is sometimes also called a PC switch or an Electronic switch. A KVM switch however, is quite different when compared to a conventional data switch. The main function of a KVM switch is to control, switch and manage many PCs via a single keyboard, monitor and mouse. When a typical PC is starting up, the operating system will automatically try to detect the signals of the keyboard and mouse. After confirmation of connectivity, the screen then displays the start up page. As a result, the start-up operations of a single PC (CPU/Server) are intricately involved with that of its keyboard and mouse.


What's KVM?


If you need to control multiple PCs, then you need to purchase several sets of keyboard, mouse and monitor. This is not the most effective management since not only is it space-consuming but also costly. Also keeping a row of large CRT monitors with keyboards and mice may be problematic. Thus the KVM switch was "born" from the demands of saving space, costs, and increasing management efficiency.

When purchasing a KVM, the choice is often based on the number of PCs that you need to control. KVMs with only a few ports are generally more convenient to use without the need for installing extra software. They can also easily be managed using hot keys or switch keys. Additionally, some of these KVMs, equipped with only a few ports, do not even need an external power supply. Due to environmental (space) needs, high-level KVM switches with multiple ports can be installed in a server rack using only 1U or 2U in space. These KVM switches can also use IP networks to manage power point outlets and control the start up or shut down of PCs.

The main function of a KVM switch is to use only one set of keyboard, monitor and mouse to start multiple PCs. It is important that the KVM switch ensures the simulated keyboard and mouse signals reach each PC and that during switching there is no affect on the PCs CPU operations. A KVM switch must also provide stable video resolution, support multiple computer platforms and operating systems, and be able to interface with many different brands of keyboards and mice. Each KVM switch can only support a maximum number of PC connections, i.e. the total number of ports. A single KVM switch can provide as few as two CPU ports, while a multiple KVM switch installation can offer more than 4000 CPU ports.

As the number of connected computers increase, the technology needs, for example signal identification, are higher in order to cope with multiple input and output signals. Correspondingly the management complexity increases as well to provide features such as Remote Control, Multiple Segmentation, and High-level Security. Remote Control solutions currently use either hardware driven KVM switches or software such as PCAnywhere, VNC, OpenSSH, and Microsoft Telnet Service. Please refer to our Remote Control Solutions column for a comparison of KVM versus Software Remote Control solutions.

Previously, KVMs have primarily been used in server rooms and data information centers equipped with multiple servers. An average-sized server room could contain 16 to 32 servers, whereas a larger server room may well contain over 100 servers. Since PCs costs are increasingly priced lower the average consumer can now afford a second or multiple PCs. Therefore, nowadays, consumers are purchasing KVMs for both convenience and space-saving needs in the home.

KVM switches are constantly evolving in order to support new needs such as advancements in technology, new specifications, innovative concepts, and new applications. Some examples of the latest KVM technologies include KVM + Peripheral / KVMP¡BKVM + Fast Ethernet / KVME, Wireless KVM, and KVM over the Net. These new KVM technologies are also increasingly popular in a consumer market exploding with new personal home technologies. Lately Digital Appliances are becoming mainstream with consumers. Multi-faceted development of KVM switches can cater to this market as well and create new concepts that may not have been previously possible.

Some basic terminology for KVM Switch specifications include:

1. Ports
The number of ports is indicative of the number of PCs that can connect to the KVM. For example, for an 8 Port KVM Switch, a single keyboard, monitor and mouse can control up to 8 PCs. Currently, the most common number of ports equipped in a KVM switch is either 2, 4, 8, 16 or 32 Ports. When the number of PCs surpasses thirty-two, cascading or daisy chaining the KVMs is then used to connect to the PCs. In order to more conveniently control and run multiple PCs, some KVM have various functions to assist in management such as hot keys, On Screen Display (OSD), and Broadcasting. Some innovative KVM companies have also developed proprietary embedded core logic chips in order to increase operational stability and the efficiency of the signal execution.

Note: Please refer to the high-end KVM feature article to find out more about connectivity.

2. Console
The console is the input/output station for a computer including monitor, keyboard and mouse (if required). However in KVM terms this refers to the control that is used to manage the keyboard, monitor and mouse of the PC. Normally, a console has three different ports for the keyboard, mouse and monitor. The specifications for the keyboard and mouse connector are USB and PS/2, whereas the specifications for the monitor are DVI and HDB 15.

Note: Some KVM Consoles supporting audio also have ports for the microphone and speakers. KVMs that are specifically designed for use with SUN and MAC computers have different ports.

This term refers to the connected PC. A single CPU port on a KVM has three different signal ports (keyboard, mouse and monitor) to connect with the ports on the PC.

In order to save on the Bill of Material (BOM) and to increase the convenience of installation, some companies manufacture their own proprietary cables combining the aforementioned three cables into one. Using three cables in one simplifies the desktop space by reducing the clutter of multiple cables. The cable signals can easily be affected by interference from external and even internal sources. Therefore it is recommended to choose a professional KVM brand to minimize these problems.

Note: KVMs that support audio also have ports for both the microphone and speakers available on the CPU/KVM port.

KVM switch categories can be divided as follows:

  • small office and home office (SOHO)
  • small and medium-sized business (SMB)
  • large or high-end global enterprise-level KVM

Many KVM companies then further divide high-end KVM to remote-controlled high-end KVM and nearby-controlled high-end KVM. For further explanation of the different types of KVMs, please visit the ATEN home page at

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