In January 1979, during the National Science Foundation (NSF) Image Analysis meeting at KPNO, the exchange format problem was discussed. P. Boyce (NSF), the chair of the meeting, urged NOAO and NRAO to come up with a solution and assigned a task force of R. Burns (NRAO), E. Groth (Princeton), and Wells to begin the process. Burns organized a meeting at the VLA of this task force and the VLA programmers. On direction from the initial session of the meeting, E. Greisen (NRAO) and Wells retired to the VLA conference room in the cafeteria building and worked together to produce the Basic FITS Agreement in 36 hours on March 27/28, 1979. It incorporated the lessons learned from the Harten and Wells prototypes. One key issue during the development process was the choice of a logical record size that would be both convenient for all machines in use at the time and would at the same time be close to filling a physical block on magnetic tape. The adopted 23040-bit logical record was an integral multiple of the word sizes of all machines then in use and was close to the 30240-bit physical block size limit of the CDC 6000/7000 series tapes. One data structure was supported: an unsigned 8-bit, signed 16-bit, or signed 32-bit integer array with 0-999 axes. However, to permit future growth, additional records were permitted to follow the data array, as long as the logical record size was the 23040-bit standard, a provision that served as the basis for the later development of extensions.
In May 1979, NOAO and NRAO exchanged FITS tapes, thereby showing that the rules of the Basic Agreement would operate in practice. The first FITS tape was written by a PL/I program executing on an IBM-360 under OS/MVT (32-bits twos complement and EBCDIC) and was successfully read by a FORTRAN program executing on a CDC-6400 under SCOPE (60-bits ones complement and Display Code), very nearly the worst possible combination of environments for interchange. This insistence on testing the format before it was presented set a precedent for future development: a practical demonstration of transfer using a proposed FITS structure is still required before it can be approved.
On June 8, 1979, Basic FITS was presented at an International Image Processing Workshop in Trieste, Italy (Wells and Greisen 1979). Harten endorsed it, it won immediate acceptance; and within one year FITS became the worldwide de facto standard in astronomy. Wells, Greisen, and Harten (1981; hereafter FITS Paper I) published the description.