A file ending in .part1.rar is the first segment of a split-volume RAR archive
Understanding the .part1.rar File – The First Piece of a Split Archive XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX.part1.rar
The .part1.rar file is not a standalone archive. It is the . Think of it like a jigsaw puzzle: you need every piece (every .partX.rar file) to assemble the original picture (the complete file). A file ending in