SQ (DOS/Windows)

SQ (DOS/Windows) is a data compression program from the early 1980s that is used on both DOS and CP/M computer systems. Data compression or bit-rate reduction involves encoding information using fewer bits than the original representation. It is a useful application because it helps reduce usage, such as data storage space or transmission capacity. Text files compressed with SQ are identified by the use of the letter “Q” in the middle initial of the file extension, and the text files ended with the extension, for example, executable files are labeled .EQE or .CQM, while text files are labeled .TQT. Groups of files compressed with SQ were often combined and stored in an archive using the LU (Library Utility) program. The archive files created from this process carried the .LBR file extensions. Individual files were compressed singly, or the LBR archive was itself compressed with SQ. Due to the development of ARC programs that combine compression and archiving, SQ became obsolete on most systems except for CP/M that lacked an ARC port.