characterized by high-speed vacuum tube as the active component technology. Operation
continued without the benefit of an operating system for a time. The mode was called "closed
shop" and was characterized by the appearance of hired operators who would select the job to be
run, initial program load the system, run the user’s program, and then select another job, and so
forth. Programs began to be written in higher level, procedure-oriented languages, and thus the
operator’s routine expanded. The operator now selected a job, ran the translation program to
assemble or compile the source program, and combined the translated object program along with
any existing library programs that the program might need for input to the linking program,
loaded and ran the composite linked program, and then handled the next job in a similar fashion.
Application programs were run one at a time, and were translated with absolute computer
addresses. There was no provision for moving a program to different location in storage for any
reason. Similarly, a program bound to specific devices could not be run at all if any of these
devices were busy or broken.
At the same time, the development of programming languages was moving away from the basic
machine languages; first to assembly language, and later to procedure oriented languages, the
most significant being the development of FORTRAN
The Second Generation, 1956-1964
The second generation of computer hardware was most notably characterized by transistors
replacing vacuum tubes as the hardware component technology. In addition, some very important
changes in hardware and software architectures occurred during this period. For the most part,
computer systems remained card and tape-oriented systems. Significant use of random access
devices, that is, disks, did not appear until towards the end of the second generation. Program
processing was, for the most part, provided by large centralized computers operated under monoprogrammed batch processing operating systems.
Themost significant innovations addressed the problem of excessive central processor delay due
to waiting for input/output operations. Recall that programs were executed by processing the
machine instructions in a strictly sequential order. As a result, the CPU, with its high speed
electronic component, was often forced to wait for completion of I/O operations which involved
mechanical devices (card readers and tape drives) that were order of magnitude slower.
Thesehardware developments led to enhancements of the operating system. I/O and data channel
communication and control became functions of the operating system, both to relieve the
application programmer from the difficult details of I/O programming and to protect the integrity
of the system to provide improved service to users by segmenting jobs and running shorter jobs
first (during "prime time") and relegating longer jobs to lower priority or night time runs. System
libraries became more widely available and more comprehensive as new utilities and application
software components were available to programmers.
The second generation was a period of intense operating system development. Also it was the
period for sequential batch processing. Researchers began to experiment with multiprogramming
The Third Generation, 1964-1979
The Third generation officially began in April 1964 with IBM’s announcement of its System/360