Network Basics: Server Form Factors

The computer networking term form factor refers to the size, shape, and packaging of a hardware device. Server computers typically come in one of three form factors:

  • Tower case: Most servers are housed in a traditional tower case, similar to the tower cases used for desktop computers. A typical server tower case is 18-inches high, 20-inches deep, and 9-inches wide and has room inside for a motherboard, five or more hard drives, and other components. Tower cases also come with built-in power supplies.

    Some server cases include advanced features specially designed for servers, such as redundant power supplies (so both servers can continue operating if one of the power supplies fails), hot-swappable fans, and hot-swappable disk drive bays. (Hot-swappable components can be replaced without powering down the server.)

  • Rack mount: If you need only a few servers, tower cases are fine. You can just place the servers next to each other on a table or in a cabinet that’s specially designed to hold servers. If you need more than a few servers, though, space can quickly become an issue. For example, what if your departmental network requires a bank of ten file servers? You’d need a pretty long table.

    Rack-mount servers are designed to save space when you need more than a few servers in a confined area. A rack-mount server is housed in a small chassis that’s designed to fit into a standard 19-inch equipment rack. The rack allows you to vertically stack servers in order to save space.

  • Blade servers: Blade servers are designed to save even more space than rack-mount servers. A blade server is a server on a single card that can be mounted alongside other blade servers in a blade chassis, which itself fits into a standard 19-inch equipment rack. A typical blade chassis holds six or more servers, depending on the manufacturer.

    One of the key benefits of blade servers is that you don’t need a separate power supply for each server. Instead, the blade enclosure provides power for all its blade servers. Some blade server systems provide rack-mounted power supplies that can serve several blade enclosures mounted in a single rack.

    In addition, the blade enclosure provides KVM switching so that you don’t have to use a separate KVM switch. You can control any of the servers in a blade server network from a single keyboard, monitor, and mouse.

    One of the biggest benefits of blade servers is that they drastically cut down the amount of cable clutter. With rack-mount servers, each server requires its own power cable, keyboard cable, video cable, mouse cable, and network cables. With blade servers, a single set of cables can service all the servers in a blade enclosure.