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Unit 1: Computer Fundamentals

programming languages were introduced during the third-generation period. Notable among Notes
these were PL/1, PASCAL, and BASIC.
We saw that second-generation computers used batch operating system. In these systems, users
had to prepare their data and programs and then submit them to a computer centre for
processing. The operator at the computer centre collected these user jobs and fed them to a
computer in batches at scheduled intervals. The respective users then collected their job’s
output from the computer centre. The inevitable delay resulting from this batch processing
approach was very frustrating to some users, especially programmers, because often they had
to wait for days to locate and correct a few program errors. To rectify this situation, John
Kemeny and Thomas Kurtz of Dartmouth College introduced the concept of timesharing
operating system. Timesharing operating system enables multiple users to directly access and
share computing resources simultaneously in a manner that each user feels that no one else
is using the computer. This is accomplished by using a large number of independent relatively
low-speed, on-line terminals connected to the main computer simultaneously. Introduction of
timesharing concept helped in drastically improving the productivity of programmers and
made on-line systems feasible, resulting in new on-line applications like airline reservation
systems, interactive query systems, etc.
Until 1965, computer manufacturers sold their hardware along with all associated software
without any separate charges for software. For example, buyers received language translators
for all languages supported on a computer they purchased. From user’s standpoint, software
was free. However, 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 language translators supported on the purchased computer. This led to the creation of
many new software houses and the beginning of an independent software industry.

Development and introduction of minicomputers also took place during the third-generation
period. Computers built until the early 1960s were mainframe systems that only very large
companies could afford to purchase and use. Clearly, a need existed for low-cost smaller
computers to fill the gaps left by the bigger, faster, and costlier mainframe systems. Several
innovators recognized this need and formed new firms in the 1960s to produce smaller
computers. Digital Equipment Corporation (DEC) introduced the first commercially available
minicomputer, the PDP-8 (Programmed Data Processor), in 1965. It could easily fit in the
corner of a room and did not require attention of a full-time computer operator. It used
timesharing operating system and a number of users could access it simultaneously from
different locations in the same building. Its cost was about one-fourth the cost of a traditional
mainframe system making it possible for smaller companies to afford computers. It confirmed
the tremendous demand for small computers for business and scientific applications, and by
1971, there were more than 25 computer manufacturers in minicomputer market.
Characteristic features of third-generation computers are as follows:

1. They were more powerful than second-generation computers. They were capable of
performing about one million instructions per second.

2. They were smaller than second-generation computers requiring smaller space.
3. They consumed less power and dissipated less heat than second-generation computers.
The rooms/areas in which third-generation computers were located still required to
be properly air-conditioned.

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