TERSE

TERSE is a data compression format used on OS/2, and on IBM mainframes. It is still in regular use on IBM mainframes to this day.

More research is needed to understand the scope of what TERSE was used for, and how many versions of it there are.

It can at least be used for single-file compression, as is done by the Advantis software listed below. This file format does not appear to have a conventional filename extension – compressed files may keep their original name.

Identification
At least some TERSE-compressed files start with bytes.

Related formats
The ZIP format documentation (APPNOTE) lists two "TERSE" compression methods:

10 - PKWARE Data Compression Library Imploding (old IBM TERSE) 18 - File is compressed using IBM TERSE (new)

So, apparently, PKWARE DCL Implode is closely related to TERSE. It's possible that this distinction is or is related to the PACK/SPACK distinction in the file type.

Software

 * TERSE utility by Michael Nagy and Advantis
 * → tersepc.zip - Collection of binaries for several platforms
 * terse.zip - OS/2 binaries
 * IBM Knowledge Center: Terse Utility
 * TerseDecompress – open source (Apache2 licensed) Java program, written by IBM, to decompress TERSE files for mainframe.

Links

 * Wikipedia article