Data input to the first version of PHOENICS, which was released in 1981, was effected by way of Fortran statements and data files. In 1984, to help PHOENICS users not only to enter data more easily but also to enjoy the assistance of on-line help, the PHOENICS Input Language was introduced. Its name was soon shortened to PIL.
It was at that time that the "Q1 file" came into existence; and PIL was the language in which the contents of the file were written.
Since that time, PIL has been continuously enriched, a particularly extensive enrichment accompanying the issue of version 1.5 in 1989, with the introduction of "advanced PIL commands", referred to as such at various points in the Encyclopaedia.
It was at this time that the so-called "general menu" came into existence, which enabled users to input data without directly using PIL. Data were supplied, instead by "pressing buttons" and "filling number boxes".
Nevertheless, PIL was still active behind the scenes; for, when the menu session ended, the PHOENICS satellite automatically wrote out a PIL-language Q1 file. This could be ignored by un-interested users; but those who recognised the advantages of so doing could inspect those files, edit them, perhaps 'parameterize' them (i.e. replace numerical values by the equivalent of algebraic symbols), and turn them to time-saving advantage in many ways.
This tradition of maintaining the accessibility and editability of the PIL-language Q1 file has persisted with later versions of PHOENICS, even though the General Menu has been replaced by the Virtual Reality Interface.
Many modern users find it most economical to use the latter to set up their geometries and to make the initial settings; but they revert thereafter to editing the resulting Q1s.
Partly so as to facilitate understanding, and partly for the convenience of persons who are familiar with the earlier versions and are inquiring about the more recent ones, the language will be presented here in historically-sequenced parts.