Device and Font Description Files (The GNU Troff Manual)

### 6.2 Device and Font Description Files

The `groff` font and output device description formats are slight extensions of those used by AT&T device-independent `troff`. In distinction to the AT&T implementation, `groff` lacks a binary format; all files are text files.125 The device and font description files for a device name are stored in a `devname` directory. The device description file is called `DESC`, and, for each font supported by the device, a font description file is called `f`, where f is usually an abbreviation of a font’s name and/or style. For example, the `ps` (PostScript) device has `groff` font description files for Times roman (`TR`) and Zapf Chancery Medium italic (`ZCMI`), among many others, while the `utf8` device (for terminal emulators) has only font descriptions for the roman, italic, bold, and bold-italic styles (`R`, `I`, `B`, and `BI`, respectively).

Device and font description files are read both by the formatter, GNU `troff`, and by output drivers. The programs delegate these files’ processing to an internal library, `libgroff`, ensuring their consistent interpretation.