IUE data was originally processed using IUESIPS (IUE Spectral Image Processing System). The data were distributed to Guest Observers in what is referred to as IUE ``GO'' format, which are variable length record binary files based on the Video Image Communication and Retrieval (VICAR) file format. These files contain a VICAR header label containing EBCDIC and binary data followed by data records of various data types. At the IUE Data Analysis Center (IUEDAC) the GO files were reformatted into fixed-length record binary files, with the header label in one file and the data records in a separate file. This format has become known as ``RDAF'' (Regional Data Analysis Facility--see above) format.
Beginning in 1993, reprocessing began of all IUE data using the new processing software known as NEWSIPS (NEW Spectral Image Processing System). The output files are archived using the FITS (Flexible Image Transfer System) format. FITS files used fixed-length logical records with an ASCII header of FITS keywords followed by data records. The extracted spectral data files use the FITS binary table extension, and the FITS IMAGE extension is used in some files for storing auxiliary data such as data quality flags. (See the NEWSIPS Image Processing Manual for more information on file formats.)
Most of our software for reading and writing data files expects your data to be in either RDAF or FITS format. There is another format that you may come across: ``SAV'' format. Generally, a user would start with RDAF format files and create SAV files at various stages of analysis. This is quite useful for high dispersion spectra; the RDAF format files are large and users often don't have sufficient disk space to keep them online for extended periods of time. The user could extract the interesting portions of the spectrum and store them in SAV files, and then delete the RDAF files.
One difficulty with RDAF and SAV format files is that they are not portable across different computer platforms (see section 2.3). For this reason, more users today tend to save data in either ASCII table files or FITS files.
We should also mention that the current IUEDAC software is supported on several platforms including VMS, UNIX, ULTRIX, MACos, and WINDOWS 3.1. When possible, we have described the known differences between these systems throughout this manual. In general, IUEDAC programs will run on any of these platforms without any modifications.