One of the most important features of Fortran programs is their portability, that is the ease with which they can be moved from one computer system to another. Now that each generation of hardware succeeds the previous one every few years, while good software often lasts for much longer, more and more programs need to be portable. The growth in computer networks is also encouraging the development of portable programs.
The first step in achieving portability is to ensure that a standard form of programming language is acceptable everywhere. This need is now widely recognised and has resulted in the development of standards for all the major programming languages. In practice, however, many of the new standards have been ignored and standard-conforming systems for languages like Basic and Pascal are still very rare.
Fortunately Fortran is in much better shape: almost all current Fortran systems are designed to conform to the standard usually called Fortran77. This was produced in 1977 by a committee of the American National Standards Institute (ANSI) and was subsequently adopted by the International Standards Organisation (ISO). The definition was published as ANSI X3.9-1978 and ISO 1539-1980. The term ``Standard Fortran" will be used in the rest of this book to refer to mean Fortran77 according to this definition.
Fortran is now one of the most widely used computer languages in the world with compilers available for almost every type of computer on the market. Since Fortran77 is quite good at handling character strings as well as numbers and also has powerful file-handling and input/output facilities, it is suitable for a much wider range of applications than before.