KVM switch
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 mouse.[1]
Name
Switches to connect multiple computers to one or more peripherals have had multiple names.
The earliest name was Keyboard Video Switch (KVS).[2] 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 (now Vertiv), a peripheral switch manufacturer, in 1995.[3] Some companies call their switches Keyboard, Video, Mouse and Peripheral (KVMP).
Types
USB keyboards, mice, and I/O devices are the most common devices connected to a KVM switch. The classes of KVM switches discussed below are based on different types of core technologies, which vary in how the KVM switch handles USB I/O devices—including keyboards, mice, touchscreen displays, etc. (USB-HID = USB human interface device)
- USB Hub Based KVM
- Also 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 similar to the process of physically plugging and unplugging a USB device into the 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. [4]
- 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.[5]
- KVM+Dock
- A KVM switch with built-in docking station. It combines two devices, a KVM switch and a docking station. The customer expectations for this kind of product has increased due to a rising number of work from home setups that need to share user I/O devices between a personal PC and work laptop as a consequence of COVID pandemic restrictions.
| Feature | Hub Base Class | Emulated Class | Semi-DDM Class | DDM Class |
|---|---|---|---|---|
| USB re-enumeration required | Required on every switch of port | No, only for keyboard/mouse | No, for all USB-HID | No, for all USB-HID |
| Latency in sharing connected USB devices | Longest, depending on connected system's OS (about 10–15 seconds) | Short | Short | No latency |
| Supports Hot-Key Command | No | Yes, only on dedicated keyboard port | Yes, all the console Semi-DDM ports | Yes, all the console DDM ports |
| Supports special keyboard and mouse functions | Limited* | No, only acts as standard keyboard/mouse | Yes | Yes |
| Windows 7/Windows 8 showing correct connected devices | Limited* | No, shows as standard keyboard and mouse no matter what keyboard/mouse are connected to the KVM | Yes | Yes |
| Windows7/Windows 8 built-in touchscreen monitor driver support | Limited* | No | Yes* | Yes |
| Wireless combo keyboard and mouse support | Limited* | No | Yes* | Yes |
| USB-HID (other than keyboard/mouse) support | Limited* | No | Yes* | Yes |
| USB touchscreen sharing support | Limited* | No | Yes* | Yes |
| Drawing tablet support | Limited* | No | Yes* | Yes |
| USB wireless unifying receiver support | Limited* | No | Yes* | Yes |
| Pros | Passes all signals between USB devices and target system/computer(s) | USB keyboard/mouse switching control, shorter switching time, Hot-Key Commands | Full USB keyboard/mouse switching control, DDM ports can work with all USB-HID class devices, Short switching time (latency: within 1 sec.), Hot-Key commands (apply to all USB Semi-DDM ports), Lower cost than Full DDM class switches | Full USB keyboard/mouse switching control, DDM ports can work with all USB-HID class devices, Shortest switching time (no latency), Hot-Key commands (apply to all USB DDM ports) |
| Cons | Longest latency, delay in device availability, Can't use USB keyboard/mouse to control KVM switching process, No Hot-Key command, Generates HPD error when switching with particular OS's | Supports only limited/fixed general keyboard and mouse profiles, Special keyboard and mouse functions will not work, Can only share "standard" USB keyboard/mouse, Can't share other USB-HID such as: touchscreen monitor, drawing tablet, etc., Generated HPD error while using other USB-HID | Still has latency when switching | Higher cost |
- 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.
- KVM+Dock
- Dual DP1.4 KVM switch with TB4 dock model will be the first model released for full-buss DisplayPort 1.4 sharing for 4K144hz gaming monitors.
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).[6] The switch 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).
In 1992–1993, Cybex Corporation engineered keyboard hot-key commands.[citation needed] Today, most KVMs are controlled through non-invasive hot-key commands (e.g. Ctrl+Ctrl, Scroll Lock+Scroll Lock and the Print Screen keys). Hot-key switching is often complemented with an on-screen display system that displays a list of connected computers.
KVM switches differ in the number of computers that can be connected. Traditional switching configurations range from 2 to 64 possible computers attached to a single device. Enterprise-grade devices interconnected via daisy-chained and/or cascaded methods can support over 1,000 devices equally accessed by any given user console.[7]D
