A KVM switch (with KVM being an abbreviation for "keyboard, video, and mouse") is a hardware device that allows a user to control multiple computers from one or more sets of keyboards, video monitors, and mice.
Name
Switches to connect multiple computers to one or more peripherals have had a variety of names.
The earliest name was Keyboard Video Switch (KVS). With the advent of the mouse, the Keyboard, Video and Mouse (KVM) switch became popular. The name was introduced by Remigius Shatas, the founder of Cybex, a peripheral switch manufacturer, in 1995. Some companies call their switches Keyboard, Video, Mouse and Peripheral (KVMP).
Types
With the popularity of USB—USB keyboards, mice, and I/O devices are still the most common devices connected to a KVM switch. The classes of KVM switches that are reviewed, are based on different types of core technologies in terms of how the KVM switch handles USB I/O devices—including keyboards, mice, touchscreen displays, etc. (USB-HID = USB Human Interface Device)
USB Hub Based KVMAlso called an Enumerated KVM switch or USB switch selector, a connected/shared USB device must go through the full initiation process (USB enumeration) every time the KVM is switched to another target system/port. The switching to different ports is just as if you were to physically plug and unplug a USB device into your targeted system. Emulated USB KVM Dedicated USB console port(s) are assigned to emulate special sets of USB keyboard or mouse switching control information to each connected/targeted system. Emulated USB provides an instantaneous and reliable switching action that makes keyboard hotkeys and mouse switching possible. However, this class of KVM switch only uses generic emulations and consequently has only been able to support the most basic keyboard and mouse features. There are also USB KVM devices that allow cross-platform operating systems and basic keyboard and mouse sharing. Semi-DDM USB KVM Dedicated USB console port(s) work with all USB-HID (including keyboard and mouse), but do not maintain the connected devices' presence to all of the targeted systems simultaneously. This class of KVM takes advantage of DDM (Dynamic Device Mapping) technology. DDM USB KVM Dedicated Dynamic device mapping USB console port(s) work with all USB-HID (including keyboard and mouse) and maintain the connected devices' special functions and characteristics to each connected/targeted system. This class of KVM switch overcomes the frustrating limitations of an Emulated USB Class KVM by emulating the true characters of the connected devices to all the computers simultaneously. This means that you can now use the extra function keys, wheels, buttons, and controls that are commonly found on modern keyboards and mice.
Limited*supported, but does not allow USB re-enumeration, which not only causes long delays in switching, but also sometimes causes HPD (Hot-Plug Device) errors to the OS system(s).
Yes*Latency time within 1 second while switching between channels/ports.
Use
A KVM Switch is a hardware device, used in data centers, that allows the control of multiple computers from a single keyboard, monitor and mouse (KVM). This switch then allows data center personnel to connect to any server in the rack. A common example of home use is to enable the use of the full-size keyboard, mouse and monitor of the home PC with a portable device such as a laptop, tablet PC or PDA, or a computer using a different operating system.
KVM switches offer different methods of connecting the computers. Depending on the product, the switch may present native connectors on the device where standard keyboard, monitor and mouse cables can be attached. Another method to have a single DB25 or similar connector that aggregated connections at the switch with three independent keyboard, monitor and mouse cables to the computers. Subsequently, these were replaced by a special KVM cable which combined the keyboard, video and mouse cables in a single wrapped extension cable. The advantage of the last approach is in the reduction of the number of cables between the KVM switch and connected computers. The disadvantage is the cost of these cables.
The method of switching from one computer to another depends on the switch. The original peripheral switches (Rose, circa 1988) used a rotary switch while active electronic switches (Cybex, circa 1990) used push buttons on the KVM device. In both cases, the KVM aligns operation between different computers and the users' keyboard, monitor and mouse (user console).