Power. Electrical power, that is. The very lifeblood of any functioning data center. It doesn't matter if it's the electricity that keeps your server at home running, or the electricity that keeps your employer in business, power is probably the single most important necessity in any IT process. You see, it doesn't matter how well you've developed the application, or how powerful your processing engines are; without electricity to run them, they may as well be boat anchors.