UTF-9 and UTF-18

UTF-9 And UTF-18

UTF-9 and UTF-18 (9- and 18-bit Unicode Transformation Format, respectively) were two April Fools' Day RFC joke specifications for encoding Unicode on systems where the nonet (nine bit group) is a better fit for the native word size than the octet, such as the 36-bit PDP-10. Both encodings were specified in RFC 4042, written by Mark Crispin (inventor of IMAP) and released on April 1, 2005. The encodings suffer from a number of flaws and it is confirmed by their author that they were intended as a joke.

However unlike some of the "specifications" given in other April 1 RFCs they are actually technically possible to implement, and have in fact been implemented in PDP-10 assembly language. They are not endorsed by the Unicode Consortium.