What's the difference between a single-monitor and dual-monitor KVM switch?

A single-monitor KVM shares one display, keyboard, and mouse between computers, while a dual-monitor (or triple-monitor) KVM extends your full multi-screen desktop across each connected machine. If you run a multi-display setup and want every screen to follow when you switch computers, you need a model explicitly rated for that number of monitors, and you'll want to confirm whether it supports extended mode versus mirror/copy mode.