Rack servers are compact computer systems designed to be mounted in a rack, which is a standardized frame that holds multiple servers. They are typically 1U to 4U in height, where "U" refers to the unit of measurement for rack space. This design allows for efficient use of space in data centers, making it easier to manage and cool multiple servers in a single location. These servers are commonly used in enterprise environments for tasks such as hosting websites, managing databases, and running applications. Their modular design enables easy upgrades and maintenance, allowing businesses to scale their operations as needed while optimizing performance and resource utilization.