Los fabricantes de computadoras especificaron la carga de calor requerida para ser manejada, el flujo requerido de aire acondicionado y la temperatura que se medirá en los puntos de entrada del gabinete. Most of the systems were installed on raised floors, with a space of approximately 1 meter or 3 feet below the floor. This allowed the air conditioning to be supplied under the floor and be expelled through the false ceiling. This space was also used for the wiring of the systems. An airlock was often provided for entry and exit.
Other components of the computer system, such as disks, also generated heat and needed to be considered. Tape drives were particularly big heat producers. It was common, in large-scale systems, for tapes and disks to be installed in a separate room, or partitioned from the mainframe, so that air conditioning requirements could be better controlled. (Printers were also partitioned, but mainly because of noise, dust, and publishing requirements.
Por ejemplo, los discos son sensibles a los cambios rápidos de humedad, ya que la condensación que se forma en la superficie del disco puede provocar que el cabezal se estrelle debido a la pequeña altura a la que vuela. Treadmills produce a lot of heat due to the powerful motors they use, but are more tolerant of changes in temperature.
Integrated circuits, or chips, introduced in the late 1960s produced a similar escalation in heat generation and tolerance. As they became more sophisticated and LSI (Large Scale Integration) became common, the escalation continued. This problem is still with us today: have you tried using a laptop on your lap lately? In addition to the increasingly sophisticated fan design, along with heat dissipators and funnels or air flow cameras, another approach has been used from time to time. This is the system we mentioned earlier, water cooling.
The computer user already provides a close tolerance power supply, sometimes at different frequencies, such as 400 Hz instead of 50 or 60. It must also supply air conditioning with temperature and humidity gradients specified within strict limits. It is now required to supply cold water, also with strict tolerances.
The computer logic circuits were assembled on multilayer PCBs (or PCAs – Printed Circuit Boards or Arrays) which were ‘plugged in’ to the backplane. The Backplane was a large multilayer printed circuit panel, of varying size, depending on the system, but normally around one meter or 3ft square. Approximately 60-100 PCBs would connect to this panel via a multipin connector, with several hundred pins, on the board.
The multilayer or backplane PCB had been necessary since the early 1970s, due to the incorporation of much more circuitry on the board. A single two -dimensional plane could not contain all the interconnections required for this multitude of circuits. The multilayer board incorporates circuitry in each layer, with links across the layers, to achieve the required connections.
For water cooling, the PCB consisted of a large heat sink, around which the circuit components were assembled, through which the chilled water flowed. When the PCB was plugged into the backplane, it also connected via special leak proof connectors to the chilled water supply flowing in the backplane. In turn, the backplane was connected with larger leak-proof connectors to the customer supply.
Today’s systems are generally physically smaller for the same computing power, and are designed to have a higher tolerance of air conditioning requirements, some in a so-called ‘office environment’. They are designed with a wind tunnel approach and require all doors to be closed.