n. 1. In software, a misfeature that becomes understandable only in historical context, as a remnant of times past retained so as not to break compatibility. Example: the retention of octal as default base for string escapes in C, in spite of the better match of hexadecimal to ASCII and modern byte-addressable architectures.
See dusty deck.
2. More restrictively, a feature with past but no present utility. Example: the force-all-caps (LCASE) bits in the V7 and BSD UNIX tty driver, designed for use with monocase terminals. In a perversion of the usual backward-compatibility goal, this functionality has actually been expanded and renamed in some later USG UNIX releases as the IUCLC and OLCUC bits.
3. The FOSSIL (Fido/Opus/Seadog Standard Interface Level) driver specification for serial-port access to replace the brain-dead routines in the IBM PC ROMs. Fossils are used by most MS-DOS BBS software in lieu of programming the bare metal of the serial ports, as the ROM routines do not support interrupt-driven operation or setting speeds above 9600. Since the FOSSIL specification allows additional functionality to be hooked in, drivers that use the hook but do not provide serial-port access themselves are named with a modifier, as in 'video fossil'.