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Unit 2: Evolution of Operating System

The 1960's – Third Generation Notes

The systems of the 1960's were also known as batch processing systems, but they were able to
take improved advantage of the computer's resources by executing numerous jobs at once. So
operating systems designers produced the concept of multiprogramming in which numerous
jobs are in main memory at once; a processor is switched from job to job as required to keep
numerous jobs advancing while keeping the peripheral devices in function.

Example: On the system without multiprogramming, when the present job paused to
wait for other I/O operation to absolute, the CPU simply sat idle until the I/O finished. The
solution for this difficulty that evolved was to partition memory into numerous pieces, with a
dissimilar job in every partition. While one job was waiting for I/O to complete, another job
could be by means of the CPU.

Another major characteristic in third-generation operating system was the technique known as
spooling (concurrent peripheral operations on line). In spooling, a high-speed device akin to a
disk interposed among a running program and a low-speed device involved with the program
in input/output. Rather than writing directly to a printer, for instance, outputs are written to the
disk. Programs can execute to completion faster, and other programs can be initiated sooner
when the printer turns out available, the outputs may be printed.

Notes Spooling technique is much like thread being spun to a spool so that it may be later
be unwound as needed.
Another trait present in this generation was time-sharing technique, a deviation of
multiprogramming technique, in which every user has an online (i.e., directly associated)
terminal. As the user is present and interacting with the computer, the computer system must
respond quickly to user requests, or else user productivity could undergo. Timesharing systems
were produced to multiprogram huge number of concurrent interactive consumers.

Fourth Generation

With the expansion of LSI (Large Scale Integration) circuits, chips, operating system appeared in
the system entered in the personal computer and the workstation age. Microprocessor technology
evolved to the peak that it turn out to be possible to construct desktop computers as influential
as the mainframes of the 1970s. Two operating systems have conquered the personal computer
scene: MS-DOS, written by Microsoft, Inc. for the IBM PC and other machines by means of the
Intel 8088 CPU and its successors, and UNIX, which is foremost on the huge personal computers
using the Motorola 6899 CPU family.

2.1.1 Operating Systems Classification

The variations and differences in the nature of different operating systems may give the impression
that all operating systems are absolutely different from each-other. But this is not true. All
operating systems contain the same components whose functionalities are almost the same. For
instance, all the operating systems perform the functions of storage management, process
management, protection of users from one-another, etc. The procedures and methods that are
used to perform these functions might be different but the fundamental concepts behind these
techniques are just the same.

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