There are several advantages in making computers as small as one can. Sometimes weight is particularly important. A modern aircraft, for example, carries quite a load of electronic apparatus. If it is possible to make any of these smaller, and therefore lighter, the aircraft can carry a bigger pay-load. This kind of consideration applies to space satellites and to all kinds of computers that have to be carried about. But weight is not the only factor. The smaller the computer the faster it can work. The signals go to and fro at a very high but almost constant speed. So if one can scale down all dimensions to, let us say, one tenth, the average lengths of the current-paths will be reduced to one tenth. So, very roughly speaking, scaling down of all linear dimensions in the ratio of one to ten also gives a valuable bonus: the speed of operation is scaled up 10 times. Other techniques allow even further speed increases. This increase of operation is a real advantage. There are some applications in which computers could be used which require very fast response times. Many of these are military, of course but military applications also have applications in engineering sooner or later. For example, automatic blind landing of aircraft requires continuous computer calculations which result in control of the aircraft flight. The more immediate the responses are, the more stable that control can be. Another advantage is that less power is required to run the computer. In space vehicles and satellites this is an important matter but even in a trial application we need not waste power. Sometimes a computer takes so much power that cooling systems which require still more power have to be installed to keep the computer from getting too hot, which would increase the risk of faults developing. So a computer which does not need to be cooled saves power on two counts. Another advantage is reliability. Mini-computers have been made possible by the development of integrated circuits. Instead of soldering bits of wire to join separate components such as resistors and capacitors sometimes in the most intricate networks, designers can now produce many connected circuits in one unit which involves no soldering and therefore no risk of broken joints at all. Which of the following is NOT one of the advantages of mini-computers?