INTRODUCTION Unless otherwise specified or discussed@ the current references to air cooling and liquid cooling are directed to such implementations on the equipment design and not at the rack or room level. It is well established that liquid cooling@ which includes most of the non-air cooling technologies@ such as water@ 2- phase/multi-phase flow and refrigerant systems@ is a much more effective method of extracting heat because@ by comparison@ air is a poor conductor of heat and has low heat capacity. These alternative cooling techniques are not new in electronic cooling@ but reinvestigated every decade or so when existing electronics technology reaches a power density plateau that cannot be adequately addressed by air cooling. The most recognized of these past liquid-cooling designs is the IBM Thermal Conduction Module (TCM) (Kraus et al. 1983) of the ??80s to the early ??90s for cooling Bipolar devices. It was abandoned when CMOS technology came along that provided continued scaling of higher performance with lower power consumption. However@ since then the server vendors brought back liquid cooling to the latest generation of DC servers because the rack power density is surpassing 30kW (102@363Btu/hr). Air cooling has always been the cooling of choice because of its beneficial attributes that are much more attractive than pure comparison of cooling performance. Some of these attributes include low cost@ ease of implementation (both in the design and equipment deployment)@ dielectric in nature@ and no adverse environmental impact. Until there is a drastic paradigm shift in the ultimate heat sinking fluid@ such as dumping the waste heat into the ocean (or lake) directly@ from a holistic view air is still the ultimate source that the heat is dissipated to and will be continued to be dumped into the environment. The industry is once again nearing the power plateau. Strong debates exist between the 2 dipoles of air cooling and liquid cooling of IT equipment and continuum of solutions in between them@ because the power density is at the transition boundary. If the power density continues its exponential growth@ the cooling sweet spot may be shifted; it will not be a debate further@ but will push the industry into liquid cooling because other issues are getting less manageable@ such as acoustic noise@ air flow distribution@ and maintaining proper local component temperatures. The market for computer and computer server units are larger than the network equipment market. Most of the commercial cooling equipment vendors are much more familiar and involved with DC environment. In this paper@ it is the main purpose to point out the differences and hope this will help vendors to derive solutions that will be tailored for CO operators instead of a 1-sizefits- all approach. Before the industry can embrace liquid cooling@ there are issues that need to be understood and addressed.