The general trend has been for equipment to pack much more performance into an increasingly smaller footprint. That trend is likely to continue. However the smaller size did not, until recently, constitute a decrease in heat load, or power requirements. In the case of DASD the heat load per square foot had been increasing enormously, and the air flow requirements along with it. This along with the tight temperature requirements of DASD made planning a necessity. That trend has seemingly reversed itself, but has not lessened the requirement for good planning. The new generation of CMOS processors require less power per MIP, but still need good clean power and properly conditioned air. Over sizing the power and HVAC systems is costly and inefficient. This becomes especially true when air conditioners run lightly loaded or UPS systems are grossly oversized. Harmonics generated by all of the newer power supplies needs to be accounted for in design parameters of all Data Center power systems. The advances in technology have brought down the cost of computing, but accentuated the need for proper planning.