Server hardware

Although servers can be built from commodity computer components—particularly for low-load and/or non-critical applications—dedicated, high-load, mission-critical servers use specialized hardware that is optimized for the needs of servers.

A server rack seen from the back
For example, servers may incorporate “industrial-strength” mechanical components such as disk drives and computer fans that provide very high reliability and performance at a correspondingly high price. Aesthetic considerations are ignored, since most servers operate in unattended computer rooms and are only visited for maintenance or repair purposes. Although servers usually require large amounts of disk space, smaller disk drives may still be used in a trade-off of capacity vs. reliability.

CPU speeds are far less critical for many servers than they are for many desktops. Not only are typical server tasks likely to be delayed more by I/O requests than processor requirements, but the lack of any graphical user interface (GUI) in many servers frees up very large amounts of processing power for other tasks, making the overall processor power requirement lower. If a great deal of processing power is required in a server, there is a tendency to add more CPUs rather than increase the speed of a single CPU, again for reasons of reliability and redundancy.

The lack of a GUI in a server (or the rare need to use it) makes it unnecessary to install expensive video adapters. Similarly, elaborate audio interfaces, joystick connections, USB peripherals, and the like are usually unnecessary.

Because servers must operate continuously and reliably, noisy but efficient and trustworthy fans may be used for ventilation instead of inexpensive and quiet fans; and in some cases, centralized air-conditioning may be used to keep servers cool, instead of or in addition to fans. Special uninterruptible power supplies may be used to ensure that the servers continue to run in the event of a power failure.

Typical servers include heavy-duty network connections in order to allow them to handle the large amounts of traffic that they typically receive and generate as they receive and reply to client requests.

The major difference between servers and desktop computers is not in the hardware but in the software. Servers often run operating systems that are designed specifically for use in servers. They also run special applications that are designed specifically to carry out server tasks.

Servers have a unique property where the more powerful and complex the system, the longer it takes for the hardware to turn on and begin loading the operating system. Servers often do extensive pre-boot memory testing and verification, along with starting up remote management services. The hard drive controllers then start up banks of drives in sequence so as not to overload the power supply with the sudden surge of everything turning on at once, then followed by RAID system prechecks for correct operation of redundancy. It is not uncommon for all these preboot hardware checks to take several minutes, but then for the machine to run continuously for months at a time.