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The Second Computer Generation

In 1955, the use of transistors  instead of vacuum tubes  marked the beginning of the second computer generation (Tanenbaum 6; Vorndran 101). At the same time, a shift from military to economic and scientific usage of computers took place (Ebeling 77). Computers such as the IBM 7094  and Siemens 2002  were less expensive than machines of the preceding generation and, more importantly, reliable enough to be sold to institutions (Tanenbaum 6; Vorndran 107). In contrast to the previous computer generation, these machines were operated and programmed by other people than those who had built them (Tanenbaum 6).⁹ Programs were no longer part of the machines (Klaeren 16). Software was programmed for the needs of each client should they not be able to do so by themselves (Zuse 124).
Although second generation computers were less expensive than their predecessors, they were still expensive enough to ensure they were used efficiently (Silberschatz and Galvin 791). In order to reduce valuable CPU idle time and setup time, programs, so-called jobs, were collected by an operator and then read onto magnetic tapes by small computers (Tanenbaum 6). These batch jobs were then read and run on expensive mainframes; results were written to a second tape which was then read by a smaller computer which printed the output (Tanenbaum 6-7, Galvin and Silberschatz 790-791). In order to save time, jobs of the same type were batched together, since each job required an interpreter of the language in which the job was written (Silberschatz and Galvin 791).
Programming was dominated by imperative languages (Bauknecht and Zehnder 164). Plugboards and direct operation from a console were replaced by punch cards, on which programmers punched their programs after they had written them on paper (Tanenbaum 6). Programs were usually written in assembly language and, later, using high-level languages like FORTRAN (mathematical FORmula TRANslating system), COBOL (COmon Business Oriented Language), and ALGOL 60 (ALGOrithmic Language which appeared in 1960) (Bauknecht and Zehnder 159-160; Tanenbaum 7).¹⁰ In contrast to first generation computers, programmers had to wait for the outcome of their efforts since they were seldomly the operators of these machines. At that time, it could take hours or even days between the writing of a program and receiving its results or, worse, still receiving only a core dump due to an error in the program (Silberschatz and Galvin 791; Tanenbaum 6).
According to Silberschatz and Galvin, the second computer generation was a first step towards the concepts of modern operating systems, providing two major functions:

• resource management (e.g. CPU time)
• shielding programmers from the complexity of the hardware.

The concepts of modern operating systems will be further discussed in section 3.1.4 later.

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