Because "chsasan" is not a common technical term, it is likely a name chosen by the creator of the archive. Common reasons for such naming conventions include:
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Programs like 7-Zip or WinZip can reconstruct the original data by right-clicking the .001 file and selecting "Extract". Possible Origins of "chsasan"
To extract the contents, you generally need all subsequent parts (e.g., .002 , .003 ) in the same folder.
The .001 file acts as the header; it contains the metadata required to join and open the rest of the volumes.
A file ending in .001 indicates that a large archive has been "spanned" or broken into smaller pieces for easier sharing or storage.