Third and Fourth generation of computer:
The third generation began in 1965 with germanium transistors being replaced by silicon transistors. Integrated circuits, circuits consisting of transistors, resistors, and grown on a single chip of silicon eliminating wired interconnection between emerged. From small-scale integrated circuits which had about 10 transistors per chip, with medium scale integrated circuits with 1OO transistors per chip. switching speed of transistors went up by a factor of 10, reliability increased by a factor of 10; power dissipation reduced by a factor of 10 and size was also reduced by a factor of 10.The cumulative effect of this was the emergence of extremely powerful CPUs with the capacity of carrying out of 1million of instructions per second. Several new architectural ideas such as virtual me interrupt the processors, base registers, etc., became part of commercial computers and extensively used.
There were significant improvements in the design of magnetic core memories. The size of main memories reached about 4 MB. Magnetic disk technology improved rapidly.100 MB drive became feasible.
The combined effect of high capacity memory, powerful CPU and large disk memories led to the development of time shared operating system. Time shared systems increased programmer productivity.
Many important on-line systems became feasible. In particular, dynamic production control systems, airline reservation systems, interactive query systems, and real-time closed loop process control systems were implemented. Integrated database management systems emerged.
High level languages improved. FORTRAN IV and optimizing FORTRAN complex were developed. COBOL 68 was standardized by the American National Standards Institute PL/1 of IBM emerged and was quite a powerful language.
The third generation probably ended by 1975. The improvements in the period 65-75 were substantial but no revolutionary new concept could be identified as heralding the end of third generation.
Main memory and hard disk went up by a factor of 4 every 3 years, Many of the features originally found in CPUs of large expensive Initial computers of he first decade of the fourth generation became part of the microprocessor architecture in the 90's. Thus, the mainframe computer of early 80s died in mid -90's. The alpha microprocessor chip designed by DEC in 1994 packed 9.3 million single chip, was driven by a 300 MHz clock and could carry out a billion operations per second. It had a built in 64 but floating point arithmetic unit, used 64 but data and 64 bit address buses. It had a built in cache memory of 64 KB and 32 registers to store temporary operands. Apart from this IBM. Apple computers and Motorola cooperated in designing a microprocessor called Power PC 600 series. Intel also designed a powerful chip in 90s called Pentium (1993) which sold in large numbers. The original Pentium was followed by Pentium with MMX (Multimedia Extension) and pentium II with a clock speed of 46 MHz and a Celeron processor with a 300 MHz clock. In 2000 Intel introduced a 64-bit processor called IA 64 or Itanium.
Microprocessors such as Pentium, Power PC, etc., are being used as the CPU of Personal Computers and portable laptop and palm held computers. Desktop workstations and powerful servers for numeric computing as well as file services use RISC microprocessors such as Alpha, MIPS and SUNSPARC.
The area of hard disk storage also saw vast improvements. 1 GB of disk on workstations became common in 1994. For larger disks RAID technology (Redundant Array of expensive Disks) was used to give storage of 100 GB. Optical disks also emerged as mass storage particularly for read only files.
Optical storage sizes were of the order of 650 MB on a 5.25" disk. New optical disks known as Digital Versatile Disk ROMs, (DVDROMs) with maximum storage capacity of around 17 GB emerged around 1998. Writable CDs were developed around the same time. The availability of optical disks at low cost saw the development of multimedia applications. Multimedia workstations were widely used.
Computer Networks came of age. The networks became very powerful with the advent of fibre optic Local Area Networks which could transmit 100 MB/sec to 1 GB/sec. Many mainframes were replaced by powerful workstations connected by a fibre optic network. Another major event during this phase was the rapid increase in the number of computers connected to the Internet. This led to the emergence of the World Wide Web which information retrieval. The Internet also brought out the need to execute programs on a variety of computers. This led to the emergence of a new object oriented language called Java. Applications written in Java, called Java applets, could be glued together with a software called Java script to create large programs.
In the area of languages, C language became popular. This was followed by a new method of design called object oriented design. The primary objectives of object oriented design are to generalize programs and to reuse objects. The C++ language emerged as the most popular object oriented language. One also saw a trend towards design of specification oriented languages. PROLOG was designed for logic oriented specification language and I-IASKELL, ML, etc., as functional specification oriented languages. With the emergence Of distributed computers connected by networks considerable effort has gone into programming distributed systems. A variety of parallel computers were built but no commonly accepted standard parallel programming language emerged.