gzip GZIP is a file archiving and compression tool associated with the .gz filename extension. The utility was first released in 1992 for the UNIX operating system, with the intention of replacing the 'compress' tool that comes bundled with UNIX. Today (2015) the tool exists as a standalone cross platform file archiver. Several archiving and compression utilities exist that support the .gz (otherwise known as gzip) format. The motivation behind the format and utility was to create a capable compression archiving tool that was unencumbered by patents of other compression algorithms that existed at the time, particularly those surrounding the LZW algorithm.
t7z The .7z filename extension is associated with the 7z compressed file archive format and the open source 7-zip compression utility both developed by Igor Pavlov. The format had its initial release in 1999. It consists of a start header 32 bytes in size which contains the signature and link to the ending header, followed by the compressed data, a metadata block, and finally the end header. 7z supports limited recovery options for 7z archive files which can open but for one reason or another cannot extract due to CRC or other data related errors.