Hardware requirements for servers vary, depending on the server application. Absolute CPU speed is not usually as critical to a server as it is to a desktop machine. Servers' duties to provide service to many users over a network lead to different requirements like fast network connections and high I/O throughput. Since servers are usually accessed over a network, they may run in headless mode without a monitor or input device. Processes that are not needed for the server's function are not used. Many servers do not have a graphical user interface (GUI) as it is unnecessary and consumes resources that could be allocated elsewhere. Similarly, audio and USB interfaces may be omitted.
Servers often run for long periods without interruption and availability must often be very high, making hardware reliability and durability extremely important. To increase reliability, most of the servers use memory with error detection and correction, redundant disks, redundant power supplies and so on. As servers need stable power supply, good Internet access, increased security and are also noisy, it is usual to store them in dedicated server centers or special rooms. It is common for a server machine to take several minutes to start up, but it may not need restarting for months or years.