About the file format .7z
7-Zip is a free and open-source modern file archiver application written by Igor Pavlov and released as freeware and Open Source software. 7-Zip was originally developed for Microsoft Windows platforms, and ported by p7zip (POSIX-7Zip) project team on Unix platforms.
7Z features very high compression ratio through powerful compression algorithms (LZMA, LZMA2, PPMd, BZip2, optionally optimized Deflate). 7z file can theoretical be up to 2^64 bytes in size, far exceeding current needs and capabilities of filesystems as currently implemented.