LEGACY SYSTEMS AND ARCHITECTURES

Legacy Systems and Architectures

Legacy Systems and Architectures

Introduction

"Operating Systems have earned the reputation for being the most critical software in a computer system”

In this paper I will be talking about:

1. The history of operating systems (OS)

2. The function of OS

3. The reason why OS are considered to be so critical

History of Operating Systems

Early History: 1940s - 1950s:

At first, computers lacked any form of operating system. The computer user had sole use of the machine. The user would arrive at the machine armed with his or her program and data, often on punched paper tape. The program would be loaded into the machine, and then the machine set to work, until the program stopped. Later, computers came with libraries of support code which were linked to the user's program to assist in operations such as input and output. This would become the start of the modern-day operating system. However, these machines still only ran a single job at a time.

Originally, each user wrote all of the code necessary to implement a particular application, including the highly detailed machine level input/output instructions. Very quickly, this input/output coding needed to implement basic functions was consolidated into an input/output control system (IOCS). Users wishing to perform input/output operations no longer had to code the instructions directly. Instead, they used IOCS routines to do the real work. This greatly simplified and sped up the coding process. The implementation of input/output control system may have been the beginning of the concept of operating system. Under this system, the user has complete control over all of main storage memory and as a result, this system has been known as the single user contiguous storage allocation system. Storage is divided into a portion holding input/output control system (IOCS) routine, a portion holding the user's program and an unused portion (Fegall, 2006).

The first single-user real storage systems were dedicated to one job for more than the jobs execution time. Job's generally required a lot of setup time during which the operating system loaded, tapes and disk packs were mounted, appropriate forms were placed in the printer and time cards been punched in. When the jobs were completed, they required considerable time to teardown, as tapes and disk packs were removed; time cards were punched out etc.... During the job setup and job teardown, the computer sat idle.

Computer users soon realized that they could cut down the amount of time wasted between the jobs, if they could automate the job-to-job transition. The first major such system, which was considered by many to be the first operating system, was designed by the General Motors Research Laboratories for their IBM 701 mainframe beginning in early 1956 . Its success helped establish batch computing - the groupings of the jobs into a single deck of cards, separated by control cards that instructed computers about the various specification of the job. The programming language that the control cards used was called job control language (JCL).

The Era of Timesharing and Multiprogramming 1960s:

The systems of ...