XRONOS is a descendant of a series of timing analysis programs written at the EXOSAT Observatory to analyse interactively the EXOSAT data on Hewlett Packard Series 1000 minicomputers. The development of XRONOS started in 1987 during the post operational phase of the EXOSAT project. XRONOS was designed to provide a timing analysis package as independent of the detectors as possible, so that it could be used for future missions with few if any changes. Some of the original design characteristics of XRONOS were deeply influenced by the experience with the analysis of large sets of high time resolution EXOSAT data. In order to limit the number of page folds, while retaining the array sizes needed, e.g., for the fast Fourier transform (FFT) of large data sets, it was decided that XRONOS should consist of a collection of programs, each dedicated to one task. Preference was initially given to a question/answer user interface.
A preliminary version of XRONOS was developed under UNIX on a Hewlett Packard 9000 computer. This was ported to VAX/VMS in 1988 to make XRONOS produce light curves within the EXOSAT database system. A test version of XRONOS, including only a small number of applications, was presented at the the first EXOSAT Database Workshop in December 1988. In response to suggestions by participants XRONOS was made more user-friendly and a command/driven user interface added which could speed up the work of experienced users. The number of XRONOS applications grew rapidly in 1989. Since early 1990 all XRONOS applications can be run from the control environment provided by the program xronos, which is characterised by 3 different user interfaces: a question/answer user interface, a simplified, partial question/answer user interface and a command-driven user interface. Moreover, all XRONOS applications are available in a command-driven fashion within the EXOSAT Database System. An intermediate version of XRONOS was presented at the Second EXOSAT Database Workshop in February 1990.
Version 3.00 (July 1992) was the first complete portable version of XRONOS and runs on VAX/VMS and SUN, DEC and NEXT UNIX machines. The current version (4.02) extends XRONOS to include FITS input and output file support.