Rack-mounted systems are computer systems designed to be installed in a standard 19-inch rack, which is a framework that holds multiple electronic devices. These systems are typically used in data centers and server rooms, allowing for efficient use of space and easy access to hardware components. Each unit, often called a rack unit or U, has a specific height measurement, making it easy to stack multiple devices vertically. This organization helps with cooling, cable management, and maintenance, making it a popular choice for businesses that require reliable and scalable computing solutions.