Font libraries are distributed with emTeX. They contain a collection of PK files. Font libraries have several advantages over a directory full of PK files: they are easier to maintain (because you don't have to deal with hundreds of files); they are faster to search (because they are indexed more efficiently than a directory); they are smaller (because each PK file wastes an average of half a cluster of disk space); and the name of each font is not limited to eight characters as it is under MS-DOS file naming conventions. Note: dvips can also use emTeX FLI files.