Zork

Zork
Zork I cover art
Developer(s)	Infocom
Publisher(s)	Personal Software Infocom
Designer(s)	Tim Anderson Marc Blank Dave Lebling Bruce Daniels
Engine	ZIL
Platform(s)	PDP-10 PDP-11 Personal computer (various)
Release	1977 (Zork) 1980 (Zork I) 1981 (Zork II) 1982 (Zork III)
Genre(s)	Adventure, interactive fiction
Mode(s)	Single-player

Zork is a text-based adventure game, first released in 1977 by developers Tim Anderson, Marc Blank, Bruce Daniels, and Dave Lebling for the PDP-10 mainframe computer. It was expanded by the original developers and others as Infocom and split into three titles—Zork I: The Great Underground Empire, Zork II: The Wizard of Frobozz, and Zork III: The Dungeon Master—which were released commercially for a variety of personal computers beginning in 1980. In the game, the player explores the abandoned Great Underground Empire in search of treasures. The game is composed of hundreds of areas, and the player moves between these areas and interacts with objects in them by typing commands which are interpreted by the game's natural language input system. The program acts as a narrator, describing the player's location and the results of the player's attempted actions. It has been described as the most famous piece of interactive fiction.

The original game, developed between 1977 and 1979 at the Massachusetts Institute of Technology (MIT), was inspired by Colossal Cave Adventure (1976), the first well-known example of interactive fiction and the first well-known well-known adventure game. The developers wanted to make a similar game that was able to understand more complicated sentences than Adventure's two-word commands. They and several other staff and students at the MIT computer center founded Infocom in 1979 to develop software programs, and Blank and Joel Berez created a way to run a smaller portion of Zork on a microcomputer. The three parts of Zork were Infocom's first products. The first episode was published by Personal Software in 1980, after which Infocom purchased back the rights and self-published all three episodes beginning in late 1981.

Zork was a massive success for Infocom, with sales increasing for years as the market for personal computers expanded. The first episode sold over 38,000 copies in 1982, and around 150,000 copies in 1984. Collectively, all three episodes sold more than 680,000 copies through 1986, making up over a third of Infocom's sales in the time period. Several more games in the Zork series were released beginning in 1987, as well as books and gamebooks. Reviews of the episodes were very positive, with several reviewers calling them the best adventure game to date. They were named to several "best of" lists in the 1990s, and in 2007, Zork was named to a list of the ten most important video games of all time, which formed the start of the game canon at the Library of Congress.

Gameplay

Zork is a text-based adventure game wherein the player explores the ruins of the Great Underground Empire (GUE) to find treasure. The player must explore the varied locations and solve puzzles by using items that they find to obtain the treasures and leave the underground empire. The player types in commands to move their character through the locations, interact with objects in the cave, pick up items to put into their inventory, and perform other actions. These commands can be one- or two-word commands like "get lantern" or can be more complex sentences like "put the lamp and sword in the case". The allowable commands are contextual to the area, or room, the player is in; for example, "get lamp" only has an effect if there is a lamp in the area. There are hundreds of rooms, each of which has a name such as "West of House" and a description, and may contain objects, obstacles, or creatures. The program acts as a narrator, describing to the player their location and the results of certain actions. If it does not understand the player's commands, it asks for the player to retype their actions.^[1] The program's replies are typically in a sarcastic, conversational tone, much as a Dungeon Master would use in leading players in a tabletop role-playing game.^[2]

The original 1977 version of the game was a single release, Zork, but when it was converted into a commercial software title the game was expanded and divided into three components, sold as Zork I: The Great Underground Empire, Zork II: The Wizard of Frobozz, and Zork III: The Dungeon Master; most of the added and expanded sections are in Zork II and III. Zork also contained multiple ways of moving between the areas used in the three episodes, which were removed in favor of a single exit at the end of each game.^[3]

Much of the game world is composed of puzzles which must be solved to continue, such as a set of buttons on a dam or a maze to be traversed. Puzzles may have more than one solution.^[1] Some areas contain monsters which the player can fight using items or weapons, and beginning in the second part of the game, released as Zork II, the player can learn magic spells to use and fight with.^[4] A thief character wanders the underground maze as well, and will steal items that the player has dropped on the ground.^[5] In dark areas, the character must carry a light source, most of which have limited uses, or else they may be eaten by a grue. The ultimate goal of each of the three episodes is to discover all of the treasures and use them to complete a final challenge. Collecting treasures earns the player points, which keep rough track of how much of the game has been completed.^[1][6][7]

Plot

Zork does not follow a linear storyline, instead relying on a set of puzzles and locations in the GUE that the player can solve in mostly any order. Location and item descriptions, as well as the manuals in later versions of the game, describe that the long before the present day, the Quendor empire, having conquered everywhere above ground, built a massive underground cave complex in order to expand the empire. Two hundred years later, the ruler Lord Dimwit Flathead renamed the empire to the Great Underground Empire and spent his reign building massive, largely pointless projects such as an underground dam and the royal museum; a century later his and his descendants' spending caused the empire to collapse and all of the residents left. The abandoned empire is the setting of the three episodes of Zork.^[8]

Zork I begins with the unnamed player character near a white house in a small, self-contained area. The player is given little instruction, but exploring the game world leads them into the Great Underground Empire. The first episode has little plot, but has nineteen treasures scattered throughout the game world behind puzzles, some of which require other treasures to solve. Placing all of the treasures into the trophy case in the white house scores the player 350 points and grants the rank of "Master Adventurer." An ancient map with further instructions then magically appears in the trophy case. These instructions provide access to a stone barrow, which is the beginning of Zork II.

In Zork II, the player character again journeys into the GUE in search of treasures, starting from the stone barrow. In this episode, the player learns through descriptions of items and areas that the GUE was ruled by the Flatheads. They also learn of the Wizard of Frobozz, who was once a respected enchanter, but when his powers began to fade was exiled by Lord Dimwit Flathead. Now gone mad and having forgotten all of his spells except those that start with the letter "F", the wizard appears randomly throughout the game and casts spells on the player, with varied effects. The player's goal, similar to the previous episode, is to solve puzzles and collect all ten treasures and then leave from the final area to the endless stair; if the player has also completed all of the optional tasks, they can reach a total of 400 points.

Zork III follows a similar pattern to the prior two episodes, but rather than just collecting treasures for their own sake, the player character is trying to gather the garb of the Dungeon Master and prove themselves as worthy of being their successor. The player collects the six items from their puzzles, with the twist that one of them, the key, must be collected before 130 actions have been taken or else it is trapped by an earthquake. Once the player has all the items, they must feed an elderly man, who reveals himself as the Dungeon Master and shows them the doorway leading to the final hallway. Once the player solves the final puzzles, getting past the Guardians of Zork and opening the Treasury of Zork, the Dungeon Master appears and transforms the player into a duplicate of himself, signifying the player's succession to his position. This episode does not give points for finding the items or optional areas, but instead gives up to seven points for taking creative steps toward solving puzzles, rather than actually solving them.

Development

MIT

Marc Blank in 2018, Bruce Daniels in 2009, and Dave Lebling in 2010

Zork was developed beginning in May 1977 by Tim Anderson, Marc Blank, Bruce Daniels, and Dave Lebling. The four were members of the Dynamic Modelling Group (DM) at the Massachusetts Institute of Technology (MIT) Laboratory for Computer Science: Anderson, Blank, and Daniels as students, and Lebling as an employee. They were inspired to create the game by Colossal Cave Adventure, a text-based adventure game which is the first well-known example of interactive fiction, as well as the first well-known adventure game. Adventure was originally created by William Crowther in 1975 and 1976, but Don Woods, a graduate student at Stanford University, expanded the game, and his version was immensely popular among the small computer-using population of the time. Historian Alexander Smith described it as "ubiquitous" on computer networks by the end of 1977.^[9] It was a big hit at MIT in early 1977, and by the end of May players had managed to completely solve it.^[10]

The four programmers began to design a game that would be a "better" text adventure game, believing that the MDL programming language that they were familiar with would be better suited to processing text inputs than the Fortran code that Crowther and Woods had used.^[10][11] The group was familiar with creating video games: Lebling had been heavily involved with Maze (1973), a multiplayer first-person shooter and the first 3D first-person game ever made, while Blank and Anderson had worked on Trivia, a multiplayer trivia game. Lebling first created a natural language input system, and Anderson and Blank built a small prototype text game to use it. The prototype was built for the Digital Equipment Corporation PDP-10 mainframe computer, the only system which supported the MDL language.^[10]

Lebling then left for a two-week vacation, and in his absence Anderson, Blank, and Daniels designed an adventure game concept, which Anderson and Blank then developed as an early version of Zork. This prototype contained many of the concepts of the final game, such as puzzles and locations found in the final game, but was simplified as, according to Anderson, "it took time for people to learn how to write good problems", and Lebling's first input system, or parser, wasn't very complex and was only "almost as smart as Adventure's". The game was unnamed, but the group had a habit of naming their programs "zork" until they were completed. The group, referring to themselves as the "implementers", continued working on the game after Lebling returned, adding features and iterating on the parser through June 1977.^[10]

The four developers did not announce their game while it was in progress, but a lack of security on the MIT systems meant that anyone who could access the PDP-10 computer over the ARPANET could see what programs were being run. As a result, there was a small community of people who would "snoop" on the system for new programs, and who then found the new "zork" adventure game and spread word of it under the name Zork. This community—dozens or possibly hundreds of players, according to Lebling—interacted with the developers as they created the game, playtesting new additions and submitting bug reports.^[4][12] The implementers added a command transcript to the game, so that they could keep track of what commands players tried to use that didn't work or what puzzles they found confusing and then try to fix the issues.^[12]

By the end of June, the game was approximately half the size of the final game, with a large community of players for the time. The group had added several sections, such as the river, volcano, and coal mine sections, and then took a break from adding new content. For the next couple months, they instead improved the engine of the game, and added the ability to save the player's progress in the game. Following user requests, they also added the ability for the game to run on other PDP-10 computers running different operating systems, TENEX and TOPS-20. These users then set up a mailing list to distribute updates to the game. The group returned to creating new content in the fall of 1977, adding the "Alice in Wonderland" section and a system for fighting enemies.^[4]

Around this time, Ted Hess at DEC decoded the protection the group had made for the source code, and another DEC employee, Bob Supnik, created a port of the game to Fortran. He released it in January 1978, thereby making the game available to a wider set up players outside of those with access to a PDP-10 mainframe. At the time, the team had decided to give the game an actual name, as "zork" had been a placeholder, and named the game Dungeon; this name was used for the Fortran version, which was spread through the DEC users group, DECUS, and became one of the most popular pieces of software distributed through the group. The name change was soon rescinded for the main game, however, as TSR Hobbies, the publishers of Dungeons & Dragons, claimed the name violated their trademark, and Zork became the official name for the game.^[4]

Over the course of 1978, the team added the final sections of the game, including the bank and the Royal Zork Puzzle Museum sections, including some puzzles and ideas suggested by players. The last puzzle was added in February of 1979, though the team continued to release bug fix updates until the final update in January of 1981. Anderson attributes this to the team running out of ideas and time, and having no more available space in the megabyte of memory allocated for the game.^[4]

Very little of the game was planned ahead of time nor were parts of the game specific to one developer; instead, whenever one of the developers had an idea they liked that developer would add it to the game, developing the concept and writing the text to go with it. Lebling claims that Blank ended up focusing mostly on the parser, Anderson on the game code, Blank and Daniels on adding puzzles, and Lebling on descriptions of areas.^[12] Anderson agrees that Blank worked mostly on the parser, claiming he wrote "40 or 50" iterations of it, and describes Daniels as designing puzzles which were then largely implemented by the others. He credits Blank with vehicles and saving, and Lebling with the robot, grues, and the fighting system.^[4] The player character was purposely left unsubscribed, with the developers removing any accidental descriptions or gendered pronouns introduced, in order to help the player be immersed in the game.^[12] The text responses to the player's commands were frequently opinionated and sarcastic as a design choice in addition to mirroring the group's speaking patterns,as they felt it would both make the system feel less like a computer and also train the player to write commands in a way that the parser could understand rather than ways it would misinterpret.^[2]

Lebling claims that the group had few direct influences when creating the game beyond Adventure, as there were few other games to emulate at the time; he does admit to basing the combat on Dungeons & Dragons, but says that the other members had never played it.^[12] The versions of the game from 1978 contain a leaflet object at the start of the game, however, that credits the game's inspiration to Adventure and Dungeons & Dragons.^[13] Lebling also thought of the parser and associated text responses as taking on the role of the Dungeon Master from a Dungeons & Dragons trying to lead the player through a story solely by describing it; this had also been the idea behind Crowther's parser in Adventure.^[2][14]

Infocom

In 1979, eight members of the Dynamic Modelling Group, including Anderson, Blank, and Lebling, incorporated Infocom as a software company for members to join after leaving MIT.^[15] No specific projects were initially agreed upon and Infocom had no paid employees, but discussions were focused on developing software for minicomputers, smaller mainframe computers.^[15][3] Blank and Joel Berez, however, having graduated and moved to Pittsburgh, came up with a plan to make Zork work on personal microcomputers, which were then beginning to become popular and which would greatly expand the audience for the game. Although microcomputers had very limited memory space compared to mainframe computers, they felt that a combination of a custom programming language for the game as well as the use of floppy disks could make the project viable if the game was cut into two pieces.^[3]

The pair worked on the project through the summer and fall of 1979 without pay, as the new company only had the funds to pay for the computers. They ported the game to a new Zork Implementation Language (ZIL), which would then be run on a standardized "Z-machine" software-based computer, with each type of microcomputer having its own interpreter program that could run the Z-Machine. This meant that getting the game to run on a different type of microcomputer just required a new interpreter program instead of rewriting the game for a different operating system. Lebling separated out half of the game from the rest, and modifications were made to the game layout to improve the flow and to remove connections from the first part of the game to what would then be separate releases.^[3]

By the end of 1979, the core game was complete, though it had only been run on DECSYSTEM-20 and PDP-11 mainframe computers, and Berez was elected the company's president. Infocom purchased a TRS-80 personal computer early in 1980, and Blank and Scott Cutler wrote an interpreter program and successfully ran the game. Infocom began preparing to release the first section of Zork under the title Zork: The Great Underground Empire - Part I, and got Mike Dornbrook to test the game as an audience surrogate, as he had never played it. He felt that the game would be wildly successful and develop a cult following, and urged Infocom to produce tie-in products like maps, hints, and shirts; while the rest of the company was not convinced enough to start producing any products, they did add an object in the game that gave an address for players to mail in for maps and hints in case it proved popular.

The game now complete, the company needed to actually publish it; feeling that self-publishing the game by building connections with stores and distributors was not a good choice, it began looking for a professional publisher. Berez approached Microsoft, but it declined as it would compete with Microsoft Adventure (1979), its version of Adventure. Microsoft CEO Bill Gates was a fan of Zork, but by the time he heard of the proposal Infocom was in negotiations with another publisher, Personal Software, one of the first professional software publishing companies. Personal Software agreed to publish the game in June 1980, sending the company an advance on the game as their first revenue. Zork: The Great Underground Empire, also known as Zork I or just Zork, was published for the TRS-80 in December 1980. The first sale of Zork I was earlier in the year, however, as since Personal Software declined to publish the PDP-11 version of the game developed in 1979 Infocom announced it to various PDP-11 user groups, and sold some copies—later recalled by Lebling as around 20—directly as a floppy disk with a typewritten manual by Anderson.^[3][2]

By the end of 1980, an Apple II version of Zork I was completed, and was also sold through Personal Software. Infocom began receiving requests for hints and maps as predicted, and Berez began handling map and poster orders while Dornbrook wrote customized hints for players; in September 1981 he found the Zork User's Group as a separate company to handle all mail-order sales and hint requests. In the meantime, Lebling worked on converting the second half of Zork into Zork II, but in the process thought up several new puzzles for the game.^[3] While as late as December 1980 he told Byte that it would be a two-part game, Zork: The Great Underground Empire - Part I and Part II, it soon became clear that the second half would not fit into the allotted space.^[5] As a result, the game was split again into Zork II: The Wizard of Frobozz and Zork III: The Dungeon Master.^[3] According to Lebling, the result of the split and additions was that each part of the game had a different atmosphere: Zork I was focused on exploration and Adventure-style gameplay, II had more of a focus on plot and added magic spells to the base game, and III was less linear, with time-sensitive aspects.^[12]

Zork II was offered to Personal Software in April 1981 and the contract signed in June, as Berez became the first paid employee of the company, but Infocom began to be wary of continuing the relationship with Personal Software. The Infocom team felt that Personal Software was not advertising Zork I very strongly, and did not seem excited about Infocom's plans to release Zork III and then follow it with several other planned text adventure games such as Deadline and Starcross. This feeling was correct, as Personal Software planned to stop publishing entertainment software altogether and rebrand as VisiCorp to align with its VisiCalc spreadsheet software, which it did in 1982. Rather than find another publisher, Infocom decided to self-publish its games and began renting office space and contracting with production facilities. It bought out Personal Software's stock of Apple II Zork I copies, and began publishing Zork I and II directly by the end of 1981. Zork III followed in the fall of 1982. Infocom developed interpreters for the Commodore 64, the Atari 8-bit family of computers, CP/M systems, and the IBM Personal Computer, and released the episodes of Zork for them as well in 1982.^[3]

Reception

Sales

The Personal Software versions of Zork I sold moderate amounts, with the TRS-80 version selling 1,500 copies in the nine months after its release in December 1980, and the Apple II version selling 6,000 copies in the same time period. After Infocom began publishing the trilogy directly, however, sales increased dramatically.^[3] Zork I was the best-selling game of 1982, with 32,000 copies sold in the first half of that year and 38,000 by the end;^[16][17][18] additionally, unlike most games, sales of the game increased over the next few years rather than decline as the market for personal computers expanded. Annual sales increased from 38,000 in 1982 to nearly 100,000 in 1983, and around 150,000 copies in 1984.^[18] Inc. reported in 1983 that the game had been a best seller for the company for years; by that point, Zork I was still making up 20 percent of Infocom's yearly sales despite 14 other released titles.^[19] Sales began to decline after that point, but it still sold well enough to reach nearly a total 380,000 copies by 1986.^[18] InfoWorld reported in April 1984 that Zork I "has returned to the top of the sales charts two years after its release".^[20] Based on sales and market-share data, Video listed it fifth on the magazine's list of best selling video games in both February^[21] and March 1985,^[22] and II Computing listed Zork I fourth on the magazine's overall list of top Apple II software as of October–November 1985, and first on the games list.^[23]

The second and third parts of Zork also sold well, though not as highly as the first: Zork II sold over 170,000 copies by 1986,^[18] while Zork III sold nearly 130,000 copies by the same date.^[18] Combined sales have been reported as more than 250,000 copies of the first three games by 1984,^[15] and more than 680,000 copies through 1986, including the 1986 Zork Trilogy release, and Zork overall comprised more than one third of Infocom's two million total game sales between 1982 and 1986. Infocom was purchased by Activision in 1986, which reported that the three Zork games and the trilogy compilation sold another 80,000 copies by early 1989.^[18]

Reviews

Byte declared in February 1981 that "no single advance in the science of Adventure has been as bold and exciting" as Zork. The magazine praised the sophisticated parser and quality of writing, stating, "That the program is entertaining, eloquent, witty, and precisely written is almost beside the point ... Zork can be felt and touched—experienced, if you will—through the care and attention to detail the authors have rendered."^[24] Jerry Pournelle recommended the game in his long-running column in the magazine in 1983, stating that "if you liked Adventure and wanted more [...] I guarantee you'll love Zork".^[25] Jon Mishcon reviewed Zork in The Space Gamer in June 1981 and said that "other than the absence of graphics, this game has no weak points I can find."^[26] Debra Marshall of 80 Micro in August 1981 called Zork "complicated and sophisticated ... a joy to play". She praised the documentation and wondered if the game could ever be completed because it "lets you do pretty much what you want to do, even if the consequences are much less than desirable".^[27] Deirdre L. Maloy reviewed the game for Computer Gaming World in January 1982, stating that "Zork is a program that is worth the money for anyone even mildly interested in adventure games."^[28]

The second and third parts were similarly praised; Softline praised Zork II's "well-balanced mix of humor, wit, and wry puns" and recommended the game to both new and experienced players.^[29] PC Magazine stated that "Zork II's appeal is universal" and that the game was challenging, enjoyable, and funny.^[30] Reviewers for K-Power in February 1984 called Zork III "the most intelligent text game for a microcomputer that we've ever seen".^[31] Carl Townsend of Creative Computing claimed in November 1983 that Zork III was the best of the trilogy.^[32] The Addison-Wesley Book of Atari Software 1984 gave all three parts of Zork an overall A+ rating, calling Zork I "THE definitive adventure game", claiming that Zork II "has the same outstanding command flexibility, wry humor, and word recognition of Zork", and concluding that Zork III was "perhaps the most entertaining of the three" and "a highwater mark for subtlety and logic".^[33]

Legacy

Zork has been described as "by far the most famous piece of [interactive fiction]" and "the father figure of the genre".^[13]

In 1992, Computer Gaming World added Zork to its Hall of Fame.^[34] In 1996, the magazine listed Zork at number 13 on their 150 best games of all-time list.^[35] Next Generation listed it as number 38 on their top 100 games of all time list that same year, and in 1999 listed the Zork series as a whole as number 48 on their top 50 games of all time list.^[36][37] On March 12, 2007, The New York Times reported that Zork was named to a list of the ten most important video games of all time, the so-called game canon, which were proposed to be archived in the Library of Congress.^[38] The Library of Congress took up this video game preservation proposal and began with the games from this list.^[39][40]

Zork was quickly followed by several more text adventure games using variants of the Zork codebase, each of which sold tens of thousands of copies at minimum.^[2][18] By 1984, three years after Infocom began self-publishing Zork I, Infocom had 50 full-time employees, US$6 million in annual sales, and 12 additional games released.^[15] By 1986 this had increased to 26 total titles, including a Zork Trilogy compilation release that included all three episodes.^[18] Infocom, however, following its initial plans to make software in general rather than just games, invested heavily in creating Cornerstone (1985), a relational database software product which had poor sales. This resulted in financial difficulties and the company being sold to Activision in 1986; it was shut down entirely in 1989.^[41]

While several of Infocom's games after Zork were referred to internally as e.g. "Zork: the Mystery" (Deadline, 1982), and "Zorks in Space" (Starcross, 1982), and Wishbringer: The Magick Stone of Dreams (1985) was ostensibly set in the same wold as Zork while Enchanter was originally internally referred to as Zork IV, the company did not make any more games explicitly in the Zork series before it was purchased. Afterwards, it created two more Zork games: Beyond Zork: The Coconut of Quendor (1987), which added a graphical map and more role-playing and combat elements, and Zork Zero: The Revenge of Megaboz (1988), a prequel game which added graphical elements and menus as well as graphical minigames. After the studio was dissolved, Activision returned to the series with several graphic adventure games: Return to Zork (1993), Zork Nemesis: The Forbidden Lands (1996), and Zork: Grand Inquisitor (1997). It additionally released Zork: The Undiscovered Underground (1997), a free text adventure game partially written by original Infocom implementors Michael Berlyn and Marc Blank to promote Zork: Grand Inquisitor, and started by never finished The Philosopher's Stone, a text adventure prequel to Zork Nemesis. In 2009, Jolt Online Gaming released Legends of Zork, a freemium browser-based online adventure game.

Zork games have been released in several compilations in addition to Zork Trilogy. The Lost Treasures of Infocom (1991) the original trilogy as well as Beyond Zork, Zork Zero, and 15 other titles, while Zork Anthology (1994) includes the original trilogy, Beyond Zork, and Zork Zero. Classic Text Adventure Masterpieces of Infocom (1996) includes all the text-based Zork games, among others.

Four gamebooks, written by Infocom developer Steve Meretzky and taking place in the Zork world, were published in 1983-1984 by Tor Books in the US and Canada, and Puffin Books in the UK: The Forces of Krill (1983), The Malifestro Quest (1983), The Cavern of Doom (1983), Conquest at Quendor (1984). These books, known collectively as the "Zork books", are presented as interactive fiction in the style of the Choose Your Own Adventure series, wherein the player makes periodic choices and turns to a page that corresponds to that choice rather than being read straight through like a novel. Additionally, six novels were published as "Infocom Books" by Avon between 1988 and 1991, two of which were directly based on Zork: The Zork Chronicles by George Alec Effinger (1990) and The Lost City of Zork by Robin W. Bailey (1991). In 1996 Threshold Entertainment acquired the rights to Zork and announced plans to create a Zork movie and live action TV series, though it was never produced.^[42][43]

External links

• Source code for a 1977 PDP-10 version of Zork

References

Sources

• Blank, Marc; Lebling, Dave (1984). Zork I – The Great Underground Empire Instruction Manual (Zork Trilogy) (PDF). Infocom.
• Blank, Marc; Lebling, Dave (1984). Zork II – The Wizard of Frobozz Instruction Manual (Zork Trilogy) (PDF). Infocom.
• Blank, Marc; Lebling, Dave (1984). Zork III – The Dungeon Master Instruction Manual (Zork Trilogy) (PDF). Infocom.
• Dibbell, Julian (1998). My Tiny Life: Crime and Passion in a Virtual World. Holt Paperbacks. ISBN 978-0-8050-3626-8. LCCN 98-13636.
• Montfort, Nick (2003). Twisty Little Passages: An Approach To Interactive Fiction. MIT Press. ISBN 978-0-262-13436-1.
• Smith, Alexander (2019). They Create Worlds: The Story of the People and Companies That Shaped the Video Game Industry, Vol. I: 1971-1982. CRC Press. ISBN 978-0-429-75261-2.
• Stanton, Jeffrey; Wells, Robert P.; Rochowansky, Sandra; Mellid, Michael, eds. (1984). The Addison-Wesley Book of Atari Software. Addison-Wesley. ISBN 0-201-16454-X.