If the level of analysis is smaller than 9, 7-Zip analyses only files that have some file name extensions: EXE, DLL, WAV. 7-Zip reads small data block at the beginning of file and tries to parse the header. It supports only some formats: WAV, PE, ELF, Mach-O. Then it can select filter that can increase compression ratio for that file.
By default 7-Zip uses x86 filters (BCJ or BCJ2) for PE files (EXE, DLL). 7-Zip doesn't use analysis in default (yx=5) mode. If (yx=7), then analysis is used for PE files, and it can increase compression ratio for files for non-x86 platforms like ARM. |