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Symbolic representation of a KVM switch. The computer on the right is currently being controlled by the peripherals. Although multiple computers are connected to the KVM, typically a smaller number of computers can be controlled at any given time.
Modern devices have also added the ability to share other peripherals like USB devices and audio. O ports in peripheral switching became prevalent. This section possibly contains original research. Please improve it by verifying the claims made and adding inline citations.
Statements consisting only of original research should be removed. O devices are still the most common devices connected to a KVM switch.
O devices—including keyboards, mice, touchscreen displays, etc. 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 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. 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.
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- Can’t share other USB-HID such as: touchscreen monitor, drawing tablet, etc.
- 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.
Driver disadvantage is the cost of video cables. The method of switching windows one kvm to another depends on the switch.
In 1992-1993, Cybex Corporation engineered keyboard hot-key commands. 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.
512 computers equally accessed by any given user console. While HDMI and DVI switches have been manufactured, VGA is still the most common video connector found with KVM switches, although many switches are now compatible with DVI connectors. Analogue switches can be built with varying capacities for video bandwidth, affecting the unit’s overall cost and quality.
A typical consumer-grade switch provides up to 200 MHz bandwidth, allowing for high-definition resolutions at 60 Hz. For analogue video, resolution and refresh rate are the primary factors in determining the amount of bandwidth needed for the signal.
The method of converting these factors into bandwidth requirements is a point of ambiguity, in part because it is dependent on the analogue nature and state of the hardware. The same piece of equipment may require more bandwidth as kvm Windows Video Driver ages due to increased degradation of the source signal. Most conversion formulas attempt to approximate the amount of bandwidth needed, including a margin of safety.
As a rule of thumb, switch circuitry should provide up to three times the bandwidth required by the original signal specification, as this allows most instances of signal loss to be contained outside the range of the signal that is pertinent to picture quality. As CRT-based displays are dependent on refresh rate to prevent flickering, they generally require more bandwidth than comparable flat panel displays. A monitor uses DDC and EDID, transmitted through specific pins, to identify itself to the system.
None: the KVM switch lacks the circuitry to handle this data, and the monitor is not «visible» to the system. The system may assume a generic monitor is attached and defaults to safe settings.
Higher resolutions and refresh rates may need to be manually unlocked through the video driver as a safety precaution. EDID information will not be able to function correctly.
EDID information that may or may not be appropriate for the monitor that is attached. Problems may arise if there is an inconsistency between the KVM’s specifications and the monitor’s, such as not being able to select desired resolutions. Pass-through: the KVM switch attempts to make communication between the monitor and the system transparent.
MCSS commands — may result in incorrect orientation of the display or improper color calibration. Microsoft guidelines recommend that KVM switches pass unaltered any I2C traffic between the monitor and the PC hosts, and do not generate HPD events upon switching to a different port while maintaining stable non-noise signal on inactive ports.
KVM switches were originally passive, mechanical devices based on multi-pole switches and some of the cheapest devices on the market still use this technology. Mechanical switches usually have a rotary knob to select between computers. KVMs typically allow sharing of two or four computers, with a practical limit of about twelve machines imposed by limitations on available switch configurations. Modern hardware designs use active electronics rather than physical switch contacts with the potential to control many computers on a common system backbone. One limitation of mechanical KVM switches is that any computer not currently selected by the KVM switch does not ‘see’ a keyboard or mouse connected to it.
Likewise, a failure to detect the monitor may result in the computer falling back to 640×480 resolution. Another problem encountered with mechanical devices is the failure of one or more switch contacts to make firm, low resistance electrical connections, often necessitating some wiggling or adjustment of the knob to correct patchy colors on screen or unreliable peripheral response. Gold-plated contacts improve that aspect of switch performance, but add cost to the device.
KVM devices provide peripheral emulation, sending signals to the computers that are not currently selected to simulate a keyboard, mouse and monitor being connected. These are used to control machines which may reboot in unattended operation. Peripheral emulation services embedded in the hardware also provides continuous support where computers require constant communication with the peripherals.
Some types of active KVM switches do not emit signals that exactly match the physical keyboard, monitor, and mouse, which can result in unwanted behavior of the controlled machines. For example, the user of a multimedia keyboard connected to a KVM switch may find that the keyboard’s multimedia keys have no effect on the controlled computers. There are software alternatives to some of the functionality of a hardware KVM switch, such as Multiplicity, Input Director and Synergy, which does the switching in software and forwards input over standard network connections.