A computer data center system (100, 300, 400, 440, 460, 500), comprising: a plurality of stacks (102, 202a, 202b, 302, 404, 504) of computers, each of the stacks having a plurality of computer motherboard assemblies arranged vertically with respect to one another; a first row (120, 402a, 402b, 442a, 442b, 402a, 462b) of stacks, the row defined by stacks arranged adjacent to each other in a horizontal line of stacks; and a cool air supply plenum (121, 304, 408, 422, 444, 466) adjacent to the first row of stacks, the cool air supply plenum (a) being arranged to supply cool air to a first side of the first row of stacks for cooling the computer motherboard assemblies placed in the stacks of the first row of stacks, and (b) having a longitudinal axis substantially parallel with an average air flow of cooling air in the plenum, wherein: (i) the stacks are arranged in a saw-tooth pattern so that the trailing corner of each stack sticks out into the airflow relative to the front corner of each stack, or (ii) the stacks are arranged in a way that each stack down said cool air supply plenum in the direction of the airflow, is stepped out into the cool air supply plenum with respect to the prior stack so that the trailing edge of a subsequent stack steps out into the cool air supply plenum more than that of the prior stack, or (iii) the air flow is provided from overhead, the face portion of each of the vertically arranged computer motherboard assemblies is stepped out into the cool air supply plenum more than one of the prior computer motherboard assemblies but less than one of the subsequent computer motherboard assemblies in the direction of the air flow. a plurality of stacks (102, 202a, 202b, 302, 404, 504) of computers, each of the stacks having a plurality of computer motherboard assemblies arranged vertically with respect to one another; a first row (120, 402a, 402b, 442a, 442b, 402a, 462b) of stacks, the row defined by stacks arranged adjacent to each other in a horizontal line of stacks; and a cool air supply plenum (121, 304, 408, 422, 444, 466) adjacent to the first row of stacks, the cool air supply plenum (a) being arranged to supply cool air to a first side of the first row of stacks for cooling the computer motherboard assemblies placed in the stacks of the first row of stacks, and (b) having a longitudinal axis substantially parallel with an average air flow of cooling air in the plenum, wherein: (i) the stacks are arranged in a saw-tooth pattern so that the trailing corner of each stack sticks out into the airflow relative to the front corner of each stack, or (ii) the stacks are arranged in a way that each stack down said cool air supply plenum in the direction of the airflow, is stepped out into the cool air supply plenum with respect to the prior stack so that the trailing edge of a subsequent stack steps out into the cool air supply plenum more than that of the prior stack, or (iii) the air flow is provided from overhead, the face portion of each of the vertically arranged computer motherboard assemblies is stepped out into the cool air supply plenum more than one of the prior computer motherboard assemblies but less than one of the subsequent computer motherboard assemblies in the direction of the air flow. (i) the stacks are arranged in a saw-tooth pattern so that the trailing corner of each stack sticks out into the airflow relative to the front corner of each stack, or (ii) the stacks are arranged in a way that each stack down said cool air supply plenum in the direction of the airflow, is stepped out into the cool air supply plenum with respect to the prior stack so that the trailing edge of a subsequent stack steps out into the cool air supply plenum more than that of the prior stack, or (iii) the air flow is provided from overhead, the face portion of each of the vertically arranged computer motherboard assemblies is stepped out into the cool air supply plenum more than one of the prior computer motherboard assemblies but less than one of the subsequent computer motherboard assemblies in the direction of the air flow.