KVM switch (with KVM being an abbreviation for Keyboard, Video or Visual Display Unit, Mouse) is
a hardware device that allows a user to control multiple computers from a single keyboard, video monitor and mouse.
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 USB devices and speakers with multiple computers.
Some KVM switches can also function in reverse - that is, a single PC can be connected to multiple monitors, keyboards, and mice. While not as common as the former, this configuration is useful when the operator wants to access a single computer from two or more (usually close) locations - for example, a public kiosk machine that also has a staff maintenance interface behind the counter, or a home office computer that doubles as a home theater PC.
A user connects a monitor, keyboard, and mouse to the KVM switch, then uses special cables (generally USB and VGA ) to connect the KVM device to the computers. Control is switched from one computer to another by the use of a switch or buttons on the KVM device, with the KVM passing the signals between the computers and the keyboard, mouse and monitor depending on which computer is currently selected. Most electronic devices also allow control to be switched through keyboard commands (such as hitting a certain key, often Scroll Lock, rapidly two or three times).
You can connect from 2 to 512 computers to a single KVM switch.
A KVM switch is useful where there are multiple computers, but no need for a dedicated keyboard, monitor and mouse for each one. They are frequently used in data centers where multiple servers are placed in a single rack with a single keyboard, monitor and mouse. A KVM 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 OS, such as a Macintosh.
Local remote KVM device design allows users to control computer equipment up to 1000 feet (300 m) away from the user consoles (keyboard, monitor and mouse). KVM over IP devices use a dedicated microcontroller and potentially specialized video capture hardware to capture the video, keyboard, and mouse signals, compress and convert them into packets, and send them over an Ethernet link to a remote console application that unpacks and reconstitutes the dynamic graphical image.
Your keyboard and mouse can be connected via USB or PS2 ports. Most modern mice and keyboards use USB interface. The drawback of using USB is that when you have a problem with your computer, PS2 is more reliable way of using your mouse or keyboard, it usually works fine even if you need to access your BIOS or when you boot into safe mode. So I recommend to buy a PS2 KVM switch.
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