- The .LBR (Library) file format was the most common form of multi-file archive on personal computers at one time. It was created by Gary P. Novosielski in 1982 for use by his LU (Library Utility) program and the author mentions benefits such as making it easier to download and distribute related files on RCPM systems as well as making better use of disk space and directory structure. .LBR reigned supreme until it was displaced by the .ARC/.ARK file format on MS-DOS and later CP/M which combined compressing member files with including them in an archive in a single process. If we look on the Walnut Creek CD we will see that the majority of multi-file archives are .LBR files.