AEA from the very start of interest in the Atlas supercomputer made it clear that this would only be possible if it had a Fortran System comparable to that available on the IBM computers. The Fortran language itself was relatively unimportant. The strength was for a language capable of sub-compilation of individual subroutines in relocatable binary format. The ability to load such routines so that the subroutines of such an executable program could be in different addresses depending on the other subroutines in use at that time. As well as the Fortran subroutines being defined as a set of cards, the relocatable binary cards of compiled subroutines should also be available on cards. The ability to include subroutines written in other languages, particularly machine code, was essential for the production of large computer programs.
Such a system made the management of large programs feasible. Changes to a subroutine did not require the whole program to be recompiled. The use of predefined libraries was made simple. the ability to share code between users working on similar programs became possible.
Defining input and output as statements in the Fortran language meant that the ability to move programs from one environment to another was significantly easier.
Alan Curtis at Harwell wrote in January 1960: FORTRAN is now more than a mere compiler, it provides a complete operating system (Monitor), an assembly program for machine language programs, for use either as FORTRAN sub-programs or autonomously, a library of sub-programs and sub-routines, and a set of program diagnostics. It is suggested that all these are really desirable. The Harwell Research Group should write the FORTRAN system. This would give it control over the facilities provided, for although all present FORTRAN facilities should be included, there is no reason why some of the restrictions of FORTRAN should not be removed and extra facilities provided. The original FORTRAN took 30 man-years of programming effort. This could be greatly reduced, but with the addition of the extra facilities incorporated in later versions it might be expected to take half this effort. This means that work should be started more or less immediately if there is a serious chance that an ATLAS will be ordered by AEA.
Ian Pyle under the direction of Alan Curtis was given the task of producing a system capable of handling the process of compiling and loading individual subroutines potentially in relocatable binary format (including subroutines in Atlas machine code and potentially compiled from other languages).
The only problem was that it needed to be available when the Atlas arrived at Chilton and there was no Atlas computer available to develop the system on.
In 1961 work started on the HARTRAN compilation system for Fortran programs on the Ferranti Atlas. The only system readily available to the Harwell team was the IBM 7090 at Risley near Manchester. The solution was to write the HARTRAN system in Fortran and run it initially on the 7090 before moving it to Atlas. This in itself is quite complicated as the FORTRAN Compiler has to be submitted to itself on the 7090 to produce the Atlas code for a Fortran compiler on Atlas and then have a rudimentary HARTRAN system on Atlas to accept it. Ian Pyle produced a paper in 1962 explaining the process. One novelty was to dummy the Fortran I/O system so that Fortran output just placed characters in a buffer that then could be read as Fortran input. Using the abilities of the Fortran I/O plus some additional library subroutines most of the work in decoding the Fortran statements could be accomplished.
The best alternative procedure would probably have been to simulate the Atlas computer on the Risley 7090. Neither approach was ideal especially as the 7090 was not on the Harwell site.
Installation of the Chilton Atlas started in June 1964 and an at risk service started in October 1964. The HARTRAN system was working on the Chilton Atlas by the end of 1964, before the official hand over of the machine in May 1965.
Fuller details of the HARTRAN system are available.
