For example, Bell Laboratories proved that mechanical brains can be built so that no wrong results are allowed to come out. In other words, the machine checks itself all the time as it goes along and stops at once if the check shows that something is wrong. This is likely to be a standard feature of new automatic thinking machinery. The frequency of failures in the machinery being designed in the laboratories may be of the order of one or two mechanical failures a week. For any type of failure an alarm circuit and trouble lights will show what part of the machine needs attention. Plug-in parts for replacement are already in use in at least two of the four mechanical brains described and should be available in all the new machines. It is possible to build a machine that will automatically change from failing equipment to properly functioning equipment. For some years though, this may be too expensive to be reasonable. The use of magnetic tape for storage reduces greatly the number of parts and so increases reliability. For example, instead of 18,000 electronic tubes in an electronic brain, there may be less than 3000. A final degree of reliability is gained when most of the time the machine operates unattended. Then, there is no human operator standing by who may fail to do the correct thing at the moment when the machine needs some attention. In fact, the motto for the room housing a mechanical brain should become, “Don’t think; let the machine do it for you.” Unattended operation from the end of one working day to the beginning of the next, with the machine changing itself from one problem to another problem, has already been proved possible on the Bell Laboratories machine. AUXILIARY DEVICES In order to use a mechanical brain, we have to give it and take from it language that it understands, _machine language_. A mechanical brain that can do 10,000 additions a second can very easily finish almost all its work at once. How can we, slow as we are, keep our friend, the giant brain, busy? We have found so far several answers to this question, none of them yet very good. Devices for preparing input will be very important. For each brain, we shall need a great many of these devices. For, at best, we type at a rate, say, of 4 characters a second, selecting any one of some 38 keys, each of which is equivalent to about 6 units of information. This is about 800 units of information per second. The machine, however, is likely to be able to gulp information from its input mechanism at the amazing rate of 60,000 units of information per second, equal to 75 people typing with no mistakes and no resting. Fortunately, at least some of the time the machine will be busy computing!