of computers. Machines whose design was initiated after 1960 (approximately). Probably the most significant criterion of difference between second generation and third generations lies in the concept of computer architecture. Generally, second generation machines were limited to what the engineers could put together and make work. Advances in electronic technology—the development of integrated circuits and the like—made it possible for designers to design an architecture to suit the requirements of the tasks envisaged for the machines and the programmers who were going to work them. With the development of the experimental machines—the IBM Stretch and the Manchester University Atlas—the concept of computer architecture became a reality. Comprehensive operating systems became, more or less, part of the machines. Multiprogramming was facilitated and much of the task of control of the memory and I/O and other resources became vested in the operating system or the machine itself.