From the early 1940's to the present, computer scientists have been able to identify clear-cut stages in the development of computer technology. With each stage radical breakthroughs in electronics occurred, with the result that the computers based on the older technology of electronics have been replaced by a newer form of machine& These stages have been referred to as generation, where each computer generation had certain unique characteristics or properties. Some of these aspects are discussed in the following paragraphs.
From first generation of vacuum, tube computers, computer design advanced through developments in hardware and software. On the hardware side, the computer changed with the replacement of vacuum tubes by transistors, the progressive miniaturisation of integrated circuitry, and the development of enhanced electronic memory. The transistor invented at Bell Laboratories in 1948, did not completely replace the vacuum tube in computers until the beginning of the 1960s. The second generation of computers was based on transistors and magnetic core memory. Although integrated circuit was developed in the late 1 950s, it was too expensive and untested for wide spread commercial use. However military applications of integrated circuits in the rocket and space flight programmes proved the reliability of integrated circuit technology.
The third generation computers based on integrated circuits and semiconductor memory, appeared in the late 1960s. From 1970s on, rapid advances in large-scale integration (LSI)of transistors on silicon chips, inexpensive random access memory (RAM), and microprocessors led to the production of powerful fourth generation mainframes, midsize minicomputers, personal computers, and workstations. Throughout this period, the steady advance of semi-conductor technology allowed the number of transistors on a chip to double every year, reaching the levels of 500,000 transistors integrated on a square centimeter. Chips with one million elements are now in production.
On the software skip, the development of operating systems, computer languages, programming techniques and applications accompanied the changes in hardware. The first computers were programmed with assembly language code. As this method was difficult and lime consuming, programming languages evolved quickly through second generation intermediate code to third generation high level languages. In 1953, John Backus at IBM developed the first high level language, FORTRAN for scientific applications. In the year 1959, Grace Hopper was mainly responsible for the creation of COBOL, a language for commercial and record-keeping applications. The movement from batch processing to time-sharing systems with terminals in the 1960s and 1970s led to the development of more interactive languages such as BASIC and APL Programmers have also written many special purpose languages for artificial intelligence (e.g., LISP and PROLOG), simulation (SNOBOL and SIMULA), and other uses.