Third Generation Computers (1964-1975)
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| Third Generation Computers (1964-1975) ) |
In 1958, Jack St. Clair Kilby and
Robert Noyce invented the first integrated circuit. Integrated circuits are
circuits consisting of several electronic components like transistors,
resistors, and capacitors grown on a single chip of silicon eliminating wired
interconnection between components. IC technology was also known as
“microelectronics” technology because it made it possible to integrate larger number
of circuit components into very small (less than 5 mm square) surface of
silicon, known as "chip". Initially the integrated circuits contained
only about ten to twenty components. This technology was named small-scale
integration(SSI). Later with the advancement in technology for manufacturing
ICs, it became possible to integrate up to abut hundred components on a single
chip. This technology was known as medium scale integration (MSI).
Third generation computers were
manufactured using ICs. Earlier ones used SSI technology and later ones used
MSI technology. ICs were smaller, less expensive to produce, more rugged and
reliable, faster in operation, dissipated less heat, and consumed less power
than circuits built by wiring electronic components manually. hence,
third generation computers were more powerful, more reliable, less expensive,
smaller, and cooler to operate than second-generation computers.
Parallel advancements in storage
technologies allowed construction of larger magnetic core based random access
memory as well as larger capacity magnetic disks and tapes. Hence,
third generation computers typically had few megabytes (less than 5 Megabytes)
of main memory and magnetic disks capable of storing few tens of megabytes of
data per disk drive.
On software front,
standardization of high-level programming languages, timesharing operating
systems, unbundling of software from hardware, and creation of an independent
software industry happened during third generation. FORTRAN and COBOL were the
most popular high-level programming languages in those days. American National
Standards Institute (ANSI) standardized them in 1966 and 1968 respectively, and
the standardized versions were called ANSI FORTRAN and ANSI COBOL. The idea was
that as long as a programmer follows these standards in program writing, he/she
could run his/her program on any computer with an ANSI FORTRAN or ANSI COBOL
compiler. Some more high-level programming languages were introduced during the
third-generation period. Notable among these were PL/1, PASCAL, and BASIC.
Second-generation computers used
batch operating system. In those 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 a computer's 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 computer simultaneously. A
separate user uses each terminal to gain direct access to the computer.
Timesharing operating system allocates CPU time in such a way that all user
programs have a brief share (known as a time slice) of CPU time in turn.
Processing speed of CPU allows it to switch from one user job to another in
rapid succession and execute a small portion of each job in allocated time
slice until the job is completed. Each user gets the illusion that he/she alone
is using the computer. Introduction of timesharing concept helped in
drastically improving the productivity of programmers and made on-line systems
feasible, resulting in new on-line applications hip airline reservation
systems, interactive query systems, etc.
Until 1965, computer
manufacturers sold their hardware along with all associated software without
separately charging 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 beg-an 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.
Another important concept
introduced during third-generation was that of backward compatible family of
computers. During this period, IBM introduced its System 360 as a family of
computers with backward compatibility as they were different sizes of mainframe
systems based on the same machine language. This enabled businesses to upgrade
their computers without incurring costs of replacing peripheral equipment and
modifying programs to run on new systems.
Development and introduction of
minicomputers also took place during third-generation. Computers built until
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 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:
- They were more powerful than second-generation computers. They were capable of performing about 1 million instructions per second.
- Third generation computers were smaller than second-generation computers requiring smaller space.
- 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.
- They were more reliable and less prone to hardware failures than second-generation computers requiring lower maintenance cost.
- They had faster and larger primary and secondary storage as compared to second-generation computers.
- They were general-purpose machines suitable for both scientific and commercial applications.
- Their manufacturing did not require manual assembly of individual components into electronic circuits resulting in reduced human labour and cost involved at assembly stage. Hence, commercial production of these systems was easier and cheaper. However, highly sophisticated technology and expensive setup was required for the manufacture of IC chips.
- Standardization of high-level programming languages allowed programs written for one computer to be easily ported to and executed on another computer.
- Timesharing operating system allowed interactive usage and simultaneous use of these systems by multiple users.
- Timesharing operating system helped in drastically improving the productivity Of programmers cutting down the time and cost of program development by several fold.
- Timesharing operating system also made on systems feasible resulting in usage of these systems for new on-line applications.
- Unbundling of software from hardware gave users of these systems an opportunity to invest only in software of their need and value.
- Third generation computers made computers affordable even by smaller companies.
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