Page 17 - DCAP403_Operating System

Operating System

Notes violations, and machine checks in addition to I/O interrupts. In addition, the interrupt
system became the technique for the user program to request services from the operating
system kernel.
5. The advent of privileged instructions allowed the operating system to maintain coordination
and control over the multiple activities now going on with in the system.
Successful implementation of multiprogramming opened the way for the development of a
new way of delivering computing services-time-sharing. In this environment, several terminals,
sometimes up to 200 of them, were attached (hard wired or via telephone lines) to a central
computer. Users at their terminals, “logged in” to the central system, and worked interactively
with the system. The system’s apparent concurrency was enabled by the multiprogramming
operating system. Users shared not only the system hardware but also its software resources and

file system disk space.
The third generation was an exciting time, indeed, for the development of both computer
hardware and the accompanying operating system. During this period, the topic of operating
systems became, in reality, a major element of the discipline of computing.

1.5.5 Fourth Generation (1979 – Present)

The fourth generation is characterised by the appearance of the personal computer and the
workstation. Miniaturisation of electronic circuits and components continued and Large Scale
Integration (LSI), the component technology of the third generation, was replaced by Very Large
Scale Integration (VLSI), which characterizes the fourth generation. VLSI with its capacity for
containing thousands of transistors on a small chip, made possible the development of desktop

computers with capabilities exceeding those that filled entire rooms and floors of building just

twenty years earlier.
The operating systems that control these desktop machines have brought us back in a full circle, to
the open shop type of environment where each user occupies an entire computer for the duration
of a job’s execution. This works better now, not only because the progress made over the years
has made the virtual computer resulting from the operating system/hardware combination so
much easier to use, or, in the words of the popular press “user-friendly.”
However, improvements in hardware miniaturisation and technology have evolved so fast that you
now have inexpensive workstation – class computers capable of supporting multiprogramming
and time-sharing. Hence the operating systems that supports today’s personal computers and
workstations look much like those which were available for the minicomputers of the third
generation.

Example: Microsoft’s DOS for IBM-compatible personal computers and UNIX for
workstation.
However, many of these desktop computers are now connected as networked or distributed
systems. Computers in a networked system each have their operating systems augmented with
communication capabilities that enable users to remotely log into any system on the network
and transfer information among machines that are connected to the network. The machines that
make up distributed system operate as a virtual single processor system from the user’s point of
view; a central operating system controls and makes transparent the location in the system of the
particular processor or processors and file systems that are handling any given program.

1.6 Summary

This unit presented the principle operation of an operating system. In this unit you had
briefly described about the history, the generations and the types of operating systems.

10 LOVELY PROFESSIONAL UNIVERSITY