We have mentioned the provisions made to provide backup power systems involving generators and battery banks (see computer history – redundancy). You can probably tell from this that we’re talking about a lot of power here.

Power means heat, and in the demanding world of the computer, excessive heat can cause all sorts of problems. Manufacturers had very tight tolerances for operating temperature and humidity.

In the early days of vacuum tubes, electronic circuits were more heat tolerant, most components could be designed to operate at high temperatures. For example, a resistor designed for quarter-watt dissipation in a current circuit could have been replaced by a 10-watt resistor of the same value in the tube design and have the same effect on the circuit. Of course, the 10 watt resistor is physically much larger, but space was not as critical as it is in today’s circuits.

However, heat generation problems were very apparent in the vacuum tube computer. The vacuum tube works by heating the cathode so that it emits electrons. The cathode is negatively charged, while the anode is positively charged.

Due to the voltage difference of a few hundred volts, the electrons are attracted to the anode and can flow freely in a vacuum. This flow is regulated by one or more grids placed between the cathode and the anode. The grid is slightly negatively biased compared to the cathode and can be modulated or modified to control the flow of electrons and thus current.

For example, in an amplifier, a triode (a tube with three electrodes, anode, cathode, and grid) can be made by applying a variable signal, perhaps from a vinyl record, to the grid. Its small variations in amplitude or size are amplified in the current flowing through the tube, usually measured through a resistor in the anode circuit.

But we got sidetracked! Back to the computer. In computers using vacuum tubes, they were generally used as a switch, on or off, 0 or 1, in tune with the binary system. This was easily accomplished by applying a negative voltage to the cathode to turn the tube off, or a more positive one to turn it on. This arrangement works well in circuits such as flip-flops and their derivatives.

But, there is always a but, due to the large number of circuits required, with each tube generating heat to function, the cooling problems were enormous. Large blowers and cooling fans around the tubes, as well as room air conditioning, were standard. Liquid cooling was also used.

When transistors first appeared in the 1960s, less heat was generated per circuit. However, with new solid-state technology came new requirements for more sophisticated designs and capabilities. The number of individual circuits multiplied.

Added to this was the narrow tolerance to temperature variations. A transistor, also normally used as a switch, could turn on when it’s supposed to be off, when it overheats, causing chaos in the system.

A transistor was not a perfectly predictable device at the time. They would perform as required within tolerances, and were individually selected for this. If it is close to the tolerance limit and in a susceptible position in the circuit or physically on the machine, a problem could occur. The air conditioning of the rooms has become very important.

In part 2 we will look at the conditions in the computer room.