What Is a KVM Switch?

A KVM switch is a piece of hardware that allows one set of peripherals (keyboard, video and mouse) to access and control numerous computers by merely adjusting a selector switch or pressing a hotkey. It's exceptionally handy in places like data centers where administrators need to quickly and conveniently access one or more of hundreds of servers.

KVM switches were first employed in the late 1980s with only keyboard and monitor inputs and outputs. Since then, KVM switch technology has advanced to include desktop KVM switches for professional and multimedia applications, rack-mounted KVM switches for data centers, KVM over IP switch technology for remote access and control, and KVM emulation software for low physical overhead.

How Does a KVM Switch Work?

KVM switches operate on either a dedicated or emulated connection between peripherals and computers. For instance, in cases of USB connections, if the administrator is working with an enumerated KVM switch, then at every change-over to another target computer, the USB connections must re-initialize the signal with the target, much like when a keyboard is unplugged and plugged back into the computer.

Emulated KVM switches, which create a general stand-in keyboard and mouse signal for target computers, remove latency created through USB enumeration. When switching over to another computer, the emulated KVM switch simply engages the stand-in signal with the connected peripherals and provides instantaneous switching. And because of emulation, keyboard hotkeys and mouse switching are made possible, allowing users to change target computers with ease.
Dynamic device mapping (DDM), the most specific of the KVM switch methods, emulates the target computers' specific and true characteristics. Compared to emulated KVM switches, which support only basic keyboard and mouse features, employing a dedicated DDM KVM maps all special keyboard functions to each connected system, allowing the use of extended keyboard functions popular in post-production and multimedia applications.

Computer access and control is another primary concern when selecting and installing a KVM switch. KVM switches are designed to allow single or multiple user access to connected systems and may allow access to systems simultaneously.

Single-user KVM switches are designed for the professional or multimedia users in charge of small server locations or remote offices. Avocent® AV100 KVM switches provide single-console control for up to 16 connected computers or servers.
Multi-user KVM switches are more common in large data centers where several administrators may be accessing servers simultaneously. Avocent® HMX High Performance KVM switches improve workflow by providing secure access and control for many users to multiple target computers while enabling administrators to maintain these resources efficiently.

KVM switches come in two main varieties based on signal output:

Analog KVM switches, which connect directly to computers, pass an analog signal to a console where administrators can then access the connected servers.
Digital KVM switches, also known as KVM over IP or IP KVM, convert analog signal to digital signal allowing access via the network or Internet using a web browser from virtually any location.

Technology Supported by KVM Switches

KVM switches support several types and styles of peripherals, an important aspect to consider when designing for the administrator user experience in data centers.

Human interface device support is comprehensive compared with the original KVM switch technology. Now, they support most standard and high-definition devices, as well as all common platforms.

Depending on the manufacturer, a KVM switch can support various video types, such as HDMI, DisplayPort, DVI, VGA, USB-C, Thunderbolt, and CatX KVM, and resolutions can reach up to 4K ultra high definition (UHD), with analog switches providing a higher resolution range than digital solutions. VGA is the most common video port support, but DVI ports are becoming more popular.

KVM switch technology can output to multiple monitors. And though dual, quad, or up to eight displays are popular configurations, with specialized KVM hardware and software, access to an unlimited number of monitors is possible. This is particularly useful in command, control, and dispatch center applications in mission-critical environments where many monitors are used for control room video walls.

Audio is another notable functionality supported by KVM switches, important for multimedia professionals.

USB input peripheral devices are the de facto standard common connection, allowing KVM switches to connect to a wide range of keyboards, mice, wireless devices, tablets, and USB storage devices. Additionally, some KVM switches have ports for PS/2 devices. In other instances, computer interface modules can be used to connect peripheral devices that don't have matching ports on the KVM switch.

While platform compatibility is not a significant concern because KVM switches are designed to be driverless and support all platforms, some switches are optimized for particular operating systems, notably Mac OS, which interface with Apple's special keyboard functionality.