International Union of Crystallography (IUCr)

An account is given of the development of theSHELXsystem of computer programs fromSHELX-76 to the present day. In addition to identifying useful innovations that have come into general use through their implementation inSHELX, a critical analysis is presented of the less-successful features, missed opportunities and desirable improvements for future releases of the software. An attempt is made to understand how a program originally designed for photographic intensity data, punched cards and computers over 10000 times slower than an average modern personal computer has managed to survive for so long.SHELXLis the most widely used program for small-molecule refinement andSHELXSandSHELXDare often employed for structure solution despite the availability of objectively superior programs.SHELXLalso finds a niche for the refinement of macromolecules against high-resolution or twinned data;SHELXPROacts as an interface for macromolecular applications.SHELXC,SHELXDandSHELXEare proving useful for the experimental phasing of macromolecules, especially because they are fast and robust and so are often employed in pipelines forhigh-throughputphasing. This paper could serve as a general literature citation when one or more of the open-sourceSHELXprograms (and the Bruker AXS versionSHELXTL) are employed in the course of a crystal-structure determination.