What Is a KVM Switch?

A KVM switch is a device that connects one keyboard, video display and mouse to several computers and lets you choose which one they control. KVM stands for keyboard, video and mouse. Each computer’s video output and USB port run to the switch, the console plugs into the other side, and pressing a button, a hotkey or picking from an on-screen menu moves the console from one computer to the next.

Most servers and rack-mounted computers only need a screen and keyboard for set-up, updates or a fault. A KVM switch lets an engineer work on any of them from one place, without a monitor and keyboard per machine or a trolley wheeled between racks. The port count sets how many computers one console can reach, typically 2 to 32, and switches can be cascaded for larger rooms.

Good switches emulate the keyboard and mouse to every computer all the time, so each one still sees a keyboard while it is not selected and switching is instant. Many also emulate the display’s EDID data, so a computer keeps its screen resolution instead of resetting each time the console moves away.

KVM switches range from a small desktop box to a whole remote-access network. The right type depends on where the computers are and where the person using them sits.

Many servers also have a KVM function built in. A baseboard management controller gives remote console access, often called iKVM, over its own network port, alongside power control and monitoring.

A KVM switch has to carry the video and USB signals of the computers it serves, so its interfaces need to match them. Older switches use VGA; current ones use HDMI, DisplayPort or DVI, and the switch sets the highest resolution and refresh rate the console can show. Dual-head and quad-head switches carry two or four displays per computer for multi-monitor work.

On the USB side, a basic switch handles a keyboard and mouse only. If the console includes a touch screen, a barcode scanner or a USB stick for updates, choose a switch with a transparent USB port that passes other devices through as well.

In industrial control rooms, KVM extenders are often paired with a switch. The computers stay in a cooled, secure equipment room, and the operator’s screens, keyboard and mouse sit at a desk tens or hundreds of metres away, connected over Cat or fibre cable. That keeps noise and heat out of the control room and keeps the hardware away from dust on the plant floor.

In a rack, a console drawer saves space and the crash cart. Our rack mount KVM consoles include 1U drawers with a 17 or 19 inch screen, and models with a built-in 16-port KVM switch, so one drawer reaches every computer in the cabinet. Where a fixed screen suits the job better, our 19 inch rack mount monitors take a VGA, HDMI or DVI feed from the switch.

For remote sites, IP KVM or a server’s built-in management controller lets an engineer reach the console without travelling. Our rack mount servers include models with a BMC that provides remote iKVM, and our explainer on what a rack server is covers the hardware around it.

Start with the computers, not the switch. These questions narrow the choice quickly:

We supply rack mount KVM console drawers and integrate them with the servers and industrial computers in your cabinet as standard, with the cable kits for each machine and every port checked before the system ships.