types of operating system

1: Batch operating system

In earlier days, computers were large machines. The common input devices are card readers, tap drivers. The common output devices were line printers punch cards and tap drives.

            The entire system worked in following manner.

-                  The OS was very simple and always resident in  main memory.

-                  Programmers would prepare a job and wait it into the operator. Job was consisted of program, data and some control information.

-                  Operator would sort them in batches with similar requirements, and as computer became available, run them batch wise.

-                  At some later time (may be after some hours or even after some days), output appeared. The output consisted of the result of the program and error appeared. Programmers needed to wait during this time, and then collect output from the operator.

Here, memory is divided in to two parts as given in following figure. It is shared between the operating system and the job. At a time, one job is selected out of the batch of jobs, and is loaded in memory for execution. Once its execution completes, another job will be selected and loaded in memory for execution. 

Introduction to disk technology made it possible to direct access to several jobs and jobs job scheduling.

Disadvantages:

-                  Low throughput: because of, CPU remains idle when I/O is going on.

-                  Programmers do not have direct interaction with job.

-                  Debugging is possible only offline, after output appears.

-                  Operations were too much time consuming.