At the end of ISO operations, in May 1998, all ISO observations (around 900 days of data) were bulk-reprocessed (BKRP) with the latest version of the pipeline and calibration software to produce the first uniform ISO Interim Archive. All products were then stored on CD-ROM jukeboxes.
During the ISO Post-Operations Phase, the data processing and calibration software had been constantly updated and improved at the rate of one major update per instrument per year as the behaviour of instruments was better understood. In order to enable the astronomical community to take advantage of these improvements, an on-the-fly reprocessing facility for all data products was provided through the interface to the archive, for the user to always have the possibility to retrieve the latest version of the data products processed with the latest version available of the pipeline software (Osuna et al. 2000, [133]).
In late 2000, all ISO observations were reprocessed again to produce the `New Interim Archive'. As technology had evolved and storage facility had become more affordable, all products were saved on hard disk which allowed faster download of the data.
All ISO data were reprocessed with the final version of the pipeline to produce the so-called `Legacy Archive'. This was released at the end of February 2002 and represents the best set of products that can be generated by an overall automated processing chain. All products were put on hard disk and previous Interim Archive and New Interim Archives were discarded.
The ISO Data Archive is constantly enhanced both in contents (Highly Processed Data Products) and functionality throughout the ISO Active Archive Phase, ending in December 2006.