Editing Z-machine (section)

===Before Z-machine===
The [[MDL (programming language)|MDL]] programming language was derived from [[Lisp (programming language)|Lisp]] at the [[Massachusetts Institute of Technology]] by the Dynamic Modeling group of the [[MIT Computer Science and Artificial Intelligence Laboratory|Laboratory for Computer Science (LCS)]] in the 1970s; inspired by ''[[Colossal Cave Adventure]]'' (1977), members of that group went on to write ''Zork'' in MDL, completing the initial version two weeks later.<ref>{{cite journal |doi=10.1109/MC.1979.1658697 |title=Zork: A Computerized Fantasy Simulation Game |first1=P. David |last1=Lebling |first2=Marc S. |last2=Blank |first3=Timothy A. |last3=Anderson |date=April 1979 |volume=12 |pages=51–59 |journal=Computer |publisher=IEEE Computer Society}}</ref><ref name=Infocom-story>{{cite web |url=http://infocom.elsewhere.org/mit-class-history/infocom-paper.pdf |title=Down From the Top of Its Game: The Story of Infocom, Inc. |first1=Hector |last1=Briceno |first2=Wesley |last2=Chao |first3=Andrew |last3=Glenn |first4=Stanley |last4=Hu |first5=Ashwin |last5=Krishnamurthy |first6=Bruce |last6=Tsuchida |publisher=MIT Course 6.933J/STS.420J (Structure of Engineering Revolutions) |date=December 15, 2000 |access-date=3 January 2025}}</ref>{{rp|5–6}} Like ''Adventure'', ''Zork'' was programmed for the [[Digital Equipment Corporation|DEC]] [[PDP-10]]; the finished version occupies 1&nbsp;MB of MDL code and requires 512&nbsp;KB of RAM to run. Because contemporary home computers did not have these resources, considerable effort was needed to port the game.<ref name=Infocom-story/>{{rp|11}} Eventually, the developers split ''Zork'' into two games for personal computers.<ref>{{cite magazine |url=https://archive.org/details/byte-magazine-1980-12/page/n173/mode/2up |title=Zork and the Future of Computerized Fantasy Simulations |first1=P. David |last1=Lebling |date=December 1980 |magazine=BYTE |pages=172–182}}</ref>

The compression required to run ''Zork'' from [[floppy disk]]s with approximately 80&nbsp;KB of storage seemed like an insurmountable barrier to Blank. Berez realized that [[UCSD Pascal]] used a [[virtual machine]] (VM) model to generate executable files that could be readily ported across platforms, and together with Blank, they devised requirements for a lightweight VM optimized for text adventure games, which would retrieve data and execute instructions as needed from storage to compensate for the relatively small RAM sizes in typical microcomputers.<ref name=Infocom-story/>{{rp|11}} The resulting Z-machine used an [[Tree (abstract data type)|object tree structure]] for in-game items, locations, characters, and weapons.<ref name=Infocom-story/>{{rp|11}} For comparison, the Z-machine parser occupies 3&nbsp;[[Byte|kB]] of storage, while the original PDP-10 parser occupies 10&nbsp;[[Word (computer architecture)|Kwords]] ([[36-bit computing|36-bit]]).<ref name=CrCo-1980/>