Average number of electronic components packed on a silicon chip doubled each year after 1965. This progress soon led to the era of large-scale integration(LSI) when it was possible to integrate over 30,000 electronic components on a single chip, followed by very-large-scale integration (VLSI) when it was possible to integrate about one million electronic components on a single chip. This progress led to a dramatic development-creation of a microprocessor. A microprocessor contains all circuits needed to perform arithmetic logic and control functions, the core activities of all computers, on a single chip. Hence, it became possible to build a complete computer with a microprocessor, few additional primary storage chips, and other support circuitry. It started a new social revolution=personal computer (PC) revolution. Overnight computers became incredibly compact. They became inexpensive to make, and suddenly it became possible for many to own a computer.
By 1978, Apple Computer Inc. and the TRS-80 model from the Radio Shack Division of Tandy corporation were dominant personal computers. By 1980, IBM realized that the personal computer market was too promising to ignore and came out with its own PC in 1981, popularly known as IBM PC. Several other manufacturers used IBM's specification and designed their own PCs, popularly known as IBM compatible PCs or clones. The IBM PC and its clones became a popular standard for the PC industry during the fourth generation.
During fourth generation, semiconductor memories replaced magnetic core memories resulting in large random access memories with very fast access time. Hard disks became cheaper, smaller, and large in capacity. In addition to magnetic tapes, floppy disks became popular as a portable medium for porting programs and data from one computer system to another.
Significant advancements also took place during fourth generation in the area of large-scale computer systems. In addition to improved processing and storage capabilities of maintain systems, the fourth-generation saw the advent of supercomputers based on parallel vector processing and symmetric multiprocessing technologies. A supercomputer based on parallel vector processing technology contains a small number of custom-designed vector processors which are connected to a number of high-speed data access shared memory modules through a custom-designed, high-bandwidth crossbar switch network. On the other hand, a supercomputer based on symmetric multiprocessing technology uses commodity microprocessors connected to a shared memory through a high-speed bus or a crossbar switch network. primary builders of supercomputers pf the former category included Cray Research and ETA Systems, where as of the latter category included IBM, Silicon Graphics, and Digital Equipment Corporation.
High-speed computer networking also developed during fourth-generation, This enabled interconnection of multiple computers for communication and sharing of data among them. Local area networks (LANs) became popular for connecting computers within an organization or within a campus. Similarly, wide area networks (WANs) became popular for connecting computers located at larger distances. This gave rise to network of computers and distributed systems.
On software front, several new developments emerged to match the new technologies of fourth generation. For example, vendors developed several new operating systems for PCs. Notable ones among these were MS-DOS. MS-Windows, and Apple's proprietary Mac OS. Since PCs were for individuals who were not computer professionals, companies developed graphical user interfaces for making computers more user friendly (easier to use). A graphical user interface (GUI) provides icons (pictures) and menus (list of choices) that users can select with a mouse. PC manufacturers and application software developers developed several new PC-based application to make PCs a powerful tool. Notable among these were powerful word processing packages that allowed easy development of documents, spreadsheet package that allowed easy manipulation and analysis of data organized in columns and rows, and graphics packages that allowed easy drawing of pictures and diagrams. Another very useful concept that became popular during fourth-generation was that of multiple windows on a single terminal screen. This features allowed users to see the status of several applications simultaneously in separate windows on same terminal screen.
In the area of software for large-scale computers, key technologies that became popular included multiprocessing operating systems and concurrent programming languages. With multiprocessing operating systems, a mainframe system could use multiple processors ( a main processor and several subordinate processors) in such a manner that the subordinate processors could manage the user terminals and peripheral devices, allowing the main processor to concentrate on processing the main program, improving the overall performance. Supercomputers also used multiprocessing operating system to extract the beast performance from the large number of processors used in these systems. Concurrent programming languages further helped in effectively using the multiprocessing capabilities of these systems by allowing programmers to write their applications in such way that different processors could execute parts of the application in parallel. The most ambitious language of this type was ADA.
During fourth-generation, the UNIX operating system also became very popular for use on large-scale systems. Additionally, due to proliferation of computer networks, several new features were included in existing operating systems to allow multiple computers on the same network to communicate with each other and share resources.
Some other software technologies that became popular during fourth-generation are C programming language, object-oriented software design, and object-oriented programming. C language combines features of high-level programming languages with effiency of an assembly language. The primary objectives of object-oriented software design are to make programs generalized and to build software systems by combaining reusable pieces of program codes called objects. To facilities object-oriented software design, several object-oriented programming languages were introduced. Out of these, C++ emerged as the most popular object-oriented language.
Characteristic features of fourth-generation computers are as follows:-
PCs were smaller and cheaper than mainframes or minicomputers of third generation.
Although the fouth-generation mainframes and supercomputers required proper air-conditioned of the rooms/area in which they were located, no air-conditioned was required for PCs.
They consumed less power than third-generation computers.
They were more eligible and less prone to hardware failures than third-generation computers requiring negligible maintenance cost.
They had faster and larger primary and secondary storage as compared to third generation computers.
They were general purpose machines.
Their manufacturing did not require manual assembly of individual components into electronic circuits resulting in reduced human labor and cost involved at assembly stage. Hence, commercial production of these systems was easier and cheaper. However, highly sophicated technology and expensive setup was required for manufacturing LSI and VLSI chips.
Use of standard high-level programming languages allowed programs written for one computer to be easily ported to and executed on another computer.
Graphical user interface (GUI) enabled new users to quickly learn how to use computers.
PC-based applications made PCs powerful tool for both office and home usage.
Network of computers enabled sharing of resources like disks, printers, etc. among multiple computers and their users. They also enabled several new types of applications involving interaction among computer users at geographically distant locations. Computer Supported Cooperative Working (CSCW),or groupware is one such application in which multiple members working on a single project and located at distant locations cooperate with each other by using a network of computers.
In addition to unbundled software, these systems also used add-on hardware feature that allowed users to invest only in the hardware configuration and software of their need and value.
PCs of fourth-generation made computers affordable even by individuals for their personal use at home.
Supercomputers of fourth-generation enabled parallel processing of different parts of an application on large number of processors used in these systems. This in turn, enabled running of time-consuming applications much faster.