KVM
Initialism of keyboard-video-mouse: a device allowing these input and output devices to be swapped between a series of server consoles, especially in a rack configuration.
KVM: one keyboard, one screen, many machines
A KVM switch is a hardware device that lets a single keyboard, video monitor, and mouse control multiple computers or servers. The operator uses a button, hotkey sequence, or on-screen menu to switch active control from one machine to another without unplugging cables or walking between workstations. In server rooms and data centers, KVMs are essential for managing dozens or hundreds of machines from a single console position.
KVM switches come in two broad categories: analog (VGA or DVI video input) and digital (HDMI, DisplayPort, USB-C). Analog switches are older and cheaper but limited to shorter cable runs before signal degradation. Modern digital KVMs support higher resolutions and refresh rates, though they cost more and require compatible ports on each connected machine. Many contemporary switches combine both legacy and modern interfaces. The number of ports typically ranges from 2 to 32, though enterprise models can control more through cascading or modular expansion.
A basic KVM switch connects one set of peripherals to several machines sequentially, like a rotary telephone selector. A KVM matrix or crosspoint switch is more complex: it allows multiple independent console sets (each with its own keyboard, monitor, and mouse) to access any connected server, and one server can be viewed on multiple consoles simultaneously. Matrix switches are much more expensive but essential in larger operations where multiple administrators need simultaneous access to different systems.
Signal integrity is the main enemy. Long cable runs, especially analog video over distances beyond 15 meters, degrade picture quality and can cause connection dropouts. Quality KVMs use buffered outputs and sometimes active circuitry to regenerate signals. Many industrial and mission-critical installations use KVMs with redundant power supplies and network-based remote access to avoid single points of failure.
The name itself is straightforward: it lists the three peripherals being switched. In networked environments, KVM functionality is increasingly provided by IP-based remote management tools (such as those built into server BMCs or intelligent PDUs), which can replace hardware KVMs for out-of-band console access. However, physical KVMs remain standard in air-gapped environments and where genuine hardware isolation between machines is required.