Introduction to Operating Systems:Early History: The 1940s and 1950s

Early History: The 1940s and 1950s

Operating systems have evolved over the last 60 years through several distinct phases or generations that correspond roughly to the decades (see the Operating Systems Thinking feature, Innovation).3 In the 1940s, the earliest electronic digital computers did not include operating systems.4, 5, 6 Machines of the time were so primitive that programmers often entered their machine-language programs one bit at a time on rows of mechanical switches. Eventually, programmers entered their machine-language programs on punched cards. Then, assembly languages—which used English-like abbreviations to represent the basic operations of the computer— were developed to speed the programming process.

General Motors Research Laboratories implemented the first operating sys- tem in the early 1950s for its IBM 701 computer.7 The systems of the 1950s generally executed only one job at a time, using techniques that smoothed the transition between jobs to obtain maximum utilization of the computer system.8 A job consti- tuted the set of program instructions corresponding to a particular computational task, such as payroll or inventory. Jobs typically executed without user input for minutes, hours or days. These early computers were called single-stream batch-processing systems, because programs and data were submitted in groups or batches by loading them consecutively onto tape or disk. A job stream processor read the job control language statements (that defined each job) and facilitated the setup of the next job. When the current job terminated, the job stream reader read in the con- trol-language statements for the next job and performed appropriate housekeeping chores to ease the transition to the next job. Although operating systems of the 1950s reduced interjob transition times, programmers often were required to directly control system resources such as memory and input/output devices. This was slow, difficult and tedious work. Further, these early systems required that an entire program be loaded into memory for the program to run. This limited pro- grammers to creating small programs with limited capabilities.9

Self Review

1. Why were assembly languages developed?

2. What limited the size and capabilities of programs in the 1950s?

Ans: 1) Assembly languages were developed to speed the programming process. They enabled programmers to specify instructions as English-like abbreviations that were easier for humans to work with than machine-language instructions. 2) The entire program had to be loaded into memory to execute. Because memory was relatively expensive, the amount of memory available to those computers was small.

Operating Systems Thinking

Innovation

Innovation is a fundamental challenge for operating systems designers. If we are going to make the massive investment required to produce new operating systems or new versions of existing operating systems, we must constantly be evaluating new technologies, new applications of computing and communications and new thinking about

how systems should be built. We have provided thousands of citations and hundreds of Web resources for you to do additional readings on topics that are of interest to you. You should con- sider belonging to professional organizations like the ACM (www.acm.org), the IEEE (www.ieee.org) and USENIX (www.usenix.org) that publish journals on the latest research and development efforts in the computer field. You should access the Web frequently to follow important developments in the field. There is always a high degree of risk when innovating, but the rewards can be substantial.