make up the bulk of the machine in a powerful installation. The power 35 consumption of these machines is also quite high, not to mention the price that runs into hundreds of thousands of dollars. The future will bring great developments in the mechanical devices associated with computer systems. For a long time these have been the weak link, from the point of view of both efficiency and reliability. 40
 Large computer systems, or mainframes,as they are referred to in the 1 field of computer science, are those computer systems found in computer installationsprocessing immense amounts of data. These powerful computers make use of very high-speed main memories into which data and programs to be dealt with are transferred for rapid 5
access. These powerful machines have a larger repertoire of more complex instructions which can be executed more quickly. Whereas smaller computers may take several steps to perform a particular operation, a larger machine may accomplish the same thing with one instruction. 10
[21 These computers can be of two types: digitalor analog.The digital computer or general-purpose computer as it is often known, makes up about 90 per cent of the large computers now in use. It gets its name because the data that are presented to it are made up of a code consisting of digits- single-character numbers. The digital computer is 15 like a gigantic cash register in that it can do calculations in steps, one after another at tremendous speed and with great accuracy. Digital computer programmingis by far the most commonly used in electronic data processingfor business or statistical purposes. The analog computer works something like a car speedometer, in that it 20
continuously works out calculations. It is used essentially for problems involving measurements. It can simulate, or imitate different measurements by electronic means. Both of these computer types - the digital and the analog - are made up of electronic components that may require a large room to accommodate them. At present, the digital 25
computer is capable of doing anything the analog once did. Moreover, it is easier to program and cheaper to operate. A new type of scientific computer system called the hybrid computerhas now been produced that combines the two types into one.
13]Really powerful computers continue to be bulky and require special 30
provision for their housing, refrigeration systems, air filtration and power supplies. This is because much more space is taken up by the input/output devices - the magnetic tape and disk units and other peripheral equipment - than by the electronic components that do not