merits of compounds, and overclockers often consider some compounds to be superior to others. The main consideration is to use the minimal amount of thermal compound required to even out surfaces, as the thermal conductivity of compound is typically 1/3 to 1/400 that of metal, though much better than air. The conductivity of the heatsink compound ranges from about 0.5 to 80W/mK (see articles); that of aluminium is about 200, that of air about 0.02. Heat-conductive pads are also used, often fitted by manufacturers to heatsinks. They are less effective than properly applied thermal compound, but simpler to apply and, if fixed to the heatsink, cannot be omitted by users unaware of the importance of good thermal contact, or replaced by a thick and ineffective layer of compound. Unlike some techniques discussed here, the use of thermal compound or padding is almost universal when dissipating significant amounts of heat. Heat sink lapping Mass-produced CPU heat spreaders and heatsink bases are never perfectly flat or smooth; if these surfaces are placed in the best contact possible, there will be air gaps which reduce heat conduction. This can easily be mitigated by the use of thermal compound, but for the best possible results surfaces must be as flat as possible. This can be achieved by a laborious process known as lapping, which can reduce CPU temperature by typically . Rounded cables Most older PCs use flat ribbon cables to connect storage drives (IDE or SCSI). These large flat cables greatly impede airflow by causing drag and turbulence. Overclockers and modders often replace these with rounded cables, with the conductive wires bunched together tightly to reduce surface area. Theoretically, the parallel strands of conductors in a ribbon cable serve to reduce crosstalk (signal carrying conductors inducing signals in nearby conductors), but there is no empirical evidence of rounding cables reducing performance. This may be because the length of the cable is short enough so that the effect of crosstalk is negligible. Problems usually arise when the cable is not electromagnetically protected and the length is considerable, a more frequent occurrence with older network cables. These computer cables can then be cable tied to the chassis or other cables to further increase airflow. This is less of a problem with new computers that use serial ATA which has a much narrower cable. Airflow The colder the cooling medium (the air), the more effective the