Z-machine

The Z-machine is a virtual machine that was used by Infocom for its text adventure games. Infocom compiled such games to files containing Z-machine instructions (called story files, or Z-code files), and could therefore port all its text adventures to a new platform simply by writing a Z-machine emulator for that platform. With the large number of incompatible home computer systems in use at the time, this was an important advantage over using native code.

The "Z" of Z-machine stands for Zork, Infocom's first adventure game. Z-code files usually have names ending in .z3, .z5, .z6 or .z8, where the number is the version number of the Z-machine on which the file is intended to be run, as given by the first byte of the story file. Previously it was common for the filenames to end with .zip (ZIP = Z-machine Interpreter Program), but this clashes with the present widespread use of .zip for PKZIP-compatible archive files.

The compiler (called Zilch) which Infocom used to produced its story files has never been released. But in May 1993, Graham Nelson released the first version of his Inform compiler, which generates Z-machine story files as its output. Inform has since become very popular in the interactive fiction community and, as a consequence, a large proportion of the interactive fiction now produced is in the form of Z-machine story files. Interpreters for these files are available on a wide variety of platforms.

During the 1990s, Graham Nelson drew up a Z-machine standard, based on detailed studies of the existing Infocom files.

External link:

• The Z-Machine Standards Document is available at http://www.gnelson.demon.co.uk/zspec/.