Computer rack cooling system

A method of operating a plurality of computers in a computer rack, comprising:

• providing a first and a second computer in a partial back-to-back relationship in the computer rack such that an overlapping portion of the back of the first computer faces an overlapping portion of the back of the second computer;
• passing cooling air through the first computer and out of an exposed portion of the back of the first computer and into a first cooling plenum or passing cooling air from the first cooling plenum into the first computer;
• and
• passing cooling air through the second computer and out of an exposed portion of the back of the second computer and into a second cooling plenum or passing cooling air from the second cooling plenum into the second computer.

A computer system, comprising:

• a computer rack;
• a first stack and a second stack provided in the computer rack, each stack comprising one or more computers;
• a first cooling plenum configured such that cooling air can flow between the computers in the first stack and the first cooling plenum;
• and
• a second cooling plenum configured such that cooling air can flow between the computers in the second stack and the second cooling plenum;
• wherein:
• the first cooling plenum is defined by an exposed portion of the back of the first stack, a first side of the second stack, and the computer rack;
• and
• the second cooling plenum is defined by an exposed portion of the back of the second stack, a first side of the first stack, and the computer rack.