Page 15 - DCAP403_Operating System

Operating System

Notes second generation – the interrupt. The data channel was able to interrupt the CPU with a
message – usually “I/O complete.” Infact, the interrupt idea was later extended from I/O to
allow signalling of number of exceptional conditions such as arithmetic overflow, division by

zero and time-run-out. Of course, interval clocks were added in conjunction with the latter, and
thus operating system came to have a way of regaining control from an exceptionally long or

indefinitely looping program.
These hardware developments led to enhancements of the operating system. I/O and data
channel communication and control became functions of the operating system, both to relieve

the application programmer from the difficult details of I/O programming and to protect the
integrity of the system to provide improved service to users by segmenting jobs and running

shorter jobs first (during “prime time”) and relegating longer jobs to lower priority or night time
runs. System libraries became more widely available and more comprehensive as new utilities
and application software components were available to programmers.
In order to further mitigate the I/O wait problem, system were set up to spool the input batch from
slower I/O devices such as the card reader to the much higher speed tape drive and similarly,
the output from the higher speed tape to the slower printer. In this scenario, the user submitted
a job at a window, a batch of jobs was accumulated and spooled from cards to tape “off line,”
the tape was moved to the main computer, the jobs were run, and their output was collected on
another tape that later was taken to a satellite computer for off line tape-to-printer output. User
then picked up their output at the submission windows.

Toward the end of this period, as random access devices became available, tape-oriented
operating system began to be replaced by disk-oriented systems. With the more sophisticated
disk hardware and the operating system supporting a greater portion of the programmer’s work,
the computer system that users saw was more and more removed from the actual hardware-
users saw a virtual machine.
The second generation was a period of intense operating system development. Also it was the
period for sequential batch processing. But the sequential processing of one job at a time remained

a significant limitation. Thus, there continued to be low CPU utilisation for I/O bound jobs and
low I/O device utilisation for CPU bound jobs. This was a major concern, since computers were
still very large (room-size) and expensive machines. Researchers began to experiment with
multiprogramming and multiprocessing in their computing services called the time-sharing
system.

Note A noteworthy example is the Compatible Time Sharing System (CTSS),
developed at MIT during the early 1960s.

Task CPU is the heart of computer system what about ALU.

1.5.4 Third Generation (1964-1979)

The third generation officially began in April 1964 with IBM’s announcement of its System/360

family of computers. Hardware technology began to use Integrated Circuits (ICs) which yielded
significant advantages in both speed and economy.

Operating system development continued with the introduction and widespread adoption of

multiprogramming. This marked first by the appearance of more sophisticated I/O buffering

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