The basic IRAF data file format is the so-called Old IRAF Format (OIF). Despite this name there is no `new' IRAF format. Most IRAF tasks use the OIF format. Some brief details of it are given below.
In IRAF version 2.11 and subsequent versions most tasks can also access data files in the widely-used international standard FITS1(Flexible Image Transport System) format.
Other formats are used for more specialised purposes. For example, the STF format is used by the STSDAS package for storing HST data, the QPOE format is used to hold photon event lists (which are usually produced by X-ray astronomy satellites) and the PLIO format for pixel lists (which flag individual pixels in an image).
The IRAF dataio package contains tasks for converting between
numerous different formats.
An Introduction to IRAF