File used by Z-machine, a game engine used for running text adventure games in the late 1970s and 80s; contains source code for games developed for the Apple II and TRS-80 Model I computers; only run by a Z-machine interpreter presently, several of which have been maintained by community members since the Z-machine was discontinued.

Z-code files use a programming language called the Zork Implementation Language (Zork was Infocom's first game). The file extensions use a numerical value for the version of the Z-machine that is used to run them. Examples include the .Z1, .Z3, .Z4, .Z5, .Z6, .Z7, and .Z8 extensions. Since version 8 was the last Z-machine version, Z8 is the most popular of the extensions. NOTE: Z2 and Z1 files are extremely rare, since very few games were released in the first and second versions of the Z-machine.