Zork was originally written at MIT for PDP-10s in an obscure Lisp dialect (MDL). The authors then later formed a company to sell the game on micro-computers. To do it, they built a virtual machine optimized for this purpose, a new Lisp dialect (ZIL) that could compile to the virtual machine, and the ported the game over to that new dialect. Even so, they had to split the game into three parts to fit.
The source you're linking to is the original MDL source. This is about the ZIL source for the three games that the original Zork was split into.
The source you're linking to is the original MDL source. This is about the ZIL source for the three games that the original Zork was split into.