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Unformatted text preview: user program is allocated a very short period of CPU time (known as a time slice) one by
one. The processing speed of the CPU allows the CPU to switch from one user job to
another in rapid succession and to execute a small portion of each job in the allocated
time slice until the job is completed. The processing speed of CPU is such that each user
gets the illusion that he/she alone is using the computer. The introduction of timesharing
concept helped in drastically improving the productivity of programmers, and also made on-line systems feasible, resulting in new on-line applications like airline reservation
systems, interactive query systems, etc.
Till 1965, computer manufacturers sold their hardware along with all the associated
software, and did not charge separately for the software they provided to customers. For
example, buyers received language translators for all the languages that could run on the
computers they purchased. From the user's standpoint, all this software was free. But the
situation changed in 1969 when IBM and other computer manufacturers began to price
their hardware and software products separately. This unbundling of software from
hardware gave users an opportunity to invest only in software of their need and value. For
example, now buyers could purchase only the language translators they needed and not
all the language translators supported on the computers they purchased. This led to the
creation of many new software houses and the beginning of an independent software
Another important concept introduced during the third-generation period was that of
upward compatible family of computers. During this period, IBM introduced its System
360 which was conceived as a family of computers with upward compatibility. That is,
the 360s were different sizes of mainframe systems based on the same machine language.
This sharing of a single machine language enabled businesses to easily upgrade their
computers without the usual costs of replacing peripheral equipment and modifying
programs to run on new systems. That is, when a company outgrew one model it could...
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This document was uploaded on 04/07/2014.
- Spring '14