Downloadable and cartridge fonts need Printer Font Metrics (PFM) and Printer Cartridge Metrics (PCM) files. These files contain the same kind of header information as Windows screen-font files, but also include extended font metrics, kerning tables, and driver-specific information. A Windows printer driver uses the information in a metrics file to prepare the width and kerning tables used by the application during composition. A font vendor must provide PFM files for downloadable fonts and PCM files for cartridges.