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.PAR File Extension

File Type 1	Parchive Index File (Most common)
File Format	File
Common?	No
File Description	Index file containing a group of parity volumes in a Parchive (or "parity volume set") archive; can be used to recover a file archive when one of the files contained in the archive is lost.
Program(s) that open par files	Mac: MacPAR deLuxe Windows: parchive; QuickPar Unix: parchive; PyPar2

File Type 2	Dedicated Micros DVR Recording
File Format	Proprietary File
Common?	No
File Description	Digital video format used by Dedicated Micros DVRs; used for both commercial and professional purposes; saved in a proprietary format that can be downloaded to a computer and viewed using NetVu software.
Program(s) that open par files	Mac: Dedicated Micros NetVu Investigator Windows: Dedicated Micros NetVu ObserVer; Dedicated Micros NetVu Investigator

Information from FileInfo.com - The File Extensions Resource.
http://www.fileinfo.com/extension/par