When using 7-Zip via the command line, the -mx switch determines the compression level. The number following "x" (ranging from 0 to 9) dictates how hard the computer works to shrink the file: No compression (Store mode). x1: Fastest compression; uses a 1 MB window size . x5: Normal compression (Default).

Ultra compression; can use up to a 256 MB window size but requires significantly more RAM and time. How to Use X1.7z Files

You can open these files using the 7-Zip File Manager or third-party tools like WinZip .

If a .7z file is too large for email or specific storage, 7-Zip can split it into smaller "chunks" (e.g., X1.7z.001 , X1.7z.002 ) which can then be rejoined. How to recover corrupted 7z archive