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SHELX is a set of programs for crystal structure determination from single-crystal diffraction data. The first version of SHELX was written at the end of the 1960's. The gradual emergence of a relatively portable FORTRAN subset enabled it to be distributed (in compressed form including test data as one box of punched cards) in 1976. SHELX-76 survived unchanged - the extremely compact globally optimized code proved resistant to mutations - until major advances in direct methods theory made an update of the structure solution part necessary (SHELXS-86). Rewriting and validating the least-squares refinement part proved more difficult, but was finally achieved with the release of SHELXL-93.

During this time operating systems such as RDOS, VMS and MSDOS, under which FORTRAN and SHELX flourished, rose and fell. Even punched cards became obsolete (except in Florida). The current version SHELX-97 is essentially upwards compatible with SHELX-76, for example the format of the reflection file remained unchanged (Microsoft please note). These programs are used in well over 50% of small-molecule structure determinations. Although SHELX was originally intended only for small molecules, improvements in computing performance and data collection methods have led to increased use of SHELX for macromolecules, especially the location of heavy atoms from MAD, SIR and SAD data using SHELXS (and recently SHELXD and SHELXE), and the refinement of proteins against high-resolution data (2.5A or better) using SHELXL.

SHELX-97 consists of the following programs:

SHELXS - Structure solution by Patterson and direct methods
SHELXC - Preparations of files for macromolecular phasing with SHELXD and SHELXE
SHELXD - Structure solution for difficult problems (and location of heavy atom sites)
SHELXE - Phases from SHELXD heavy atom sites (and density modification)
SHELXL - Structure refinement (the version SHELXH is for large structures)
CIFTAB - Tables for publication via (small molecule) CIF format
SHELXA - Post-absorption corrections (for emergency use only)
SHELXPRO - Protein interface to SHELX
SHELXWAT - Automatic water divining for macromolecules