FIT2D was originally developed on a VAX running VMS, but was later been ported Sun and HP versions of Unix67, and versions for all common versions of Unix (Dec-OSF1/Dec-Unix, Dec-Ultrix, HPUX-9, HPUX-10, IBM AIX4, Linux, Silicon Graphics IRIX5.3, Silicon Graphics IRIX6.2 SunOS4, SunOS5.4/Solaris) have been produced.
FIT2D has been ported to Windows systems, and versions have run on all systems from Windows 95 onwards. Presently the best supported and tested version is for Windows XP, but since I have a home system running Windows 98 I can test that versions run well on Windows 98.
Since Macintosh have now changed to using a Unix based operating system, I have been able to help Macintosh users to produce a Macintosh version.
The vast majority of the code is written in Fortran-77 (plus the MIL-STD-1753 extensions), and is highly portable from one system to another. (As its written in Fortran the frequency of bugs is smaller than a correspondingly sized "C" program as pointers are much less necessary, and run-time array bound checking allows most of the worst bugs to be trapped before they do any harm.) A small amount of code is written in ANSI-C for interfacing to certain POSIX system calls and the X-11 library. The code also exists as automatically converted Fortran-90, and it is hoped soon to be able to use exclusively Fortran-90 instead of Fortran-77 and take advantage of its very powerful features.
FIT2D is not in any sense Unix dependent (as a good program should not be operating system dependent), however they are to a limited extent POSIX 1003.1 dependent (POSIX 1003.1 being an international standard). For Windows systems low level equvalents to POSIX calls have been used where necessary.