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There are now two types of interactive stories on the market: high-resolution ones that display colorful pictures on the screen, and text-only games that show just words. Judging from recent sales, the text programs are more popular. Deadline (price: $49.95) has sold more than 75,000 copies since it was released by Infocom almost two years ago. The company's three-part fantasy adventure, Zork, is doing even better. The first episode, Zork I, is the bestselling piece of recreational computer software on the market, with sales of 250,000 copies. It is currently outpacing the home versions of such arcade hits as Zaxxon and Frogger. "Whizbang graphics may be easier to sell to the uninitiated, but they are being replaced by games that give a sense of realism," says Marc Blank, the 29-year-old M.I.T. alumnus who wrote Deadline and is co-author of Zork.
The key to interactive fiction is the parser, the part of the computer program that interprets the player's commands. Parsers originally accepted only one-and two-word commands ("Take sword, Kill troll"), a most frustrating limitation. In 1977, a group of M.I.T. graduates, including Blank, began working on more powerful parsers.
Using programming techniques developed at the university's artificial-intelligence laboratory, they added adjectives, prepositions and compound verbs, allowing such full sentences as "Pick up the red bomb and put it in the mailbox" and "Where is the missing will?"
Their first game, Zork, was developed on one of M.I.T.'s huge mainframe computers. The next task was to squeeze the program down so that it would run on a microcomputer with one-thousandth as much processing power. Blank, who had been studying medicine when he helped write Zork, did the necessary programming while serving his internship.
With Zork and Deadline already big hits, newer and more colorful computer novels are appearing on the software bestseller lists.
Stuart Galley, an Infocom programmer, has written a detective story, The Witness, in the hard-boiled style of Raymond Chandler.
Infidel, by Michael Berlyn, is an archaeological adventure set in modern Egypt. Planetfall, by Steven Meretzky, is a science-fiction comedy that co-stars a robot named Floyd.
By literary standards, Infocom's stories are crude. The characters are two-dimensional, plots are forever clunking to a halt, and the writing tends to be sophomoric. Perhaps the best computer thriller to date is Suspended, also by Berlyn, a published author with several science-fiction books to his credit. With computer novels selling better than many hardcover books, it may not be long before the new genre attracts an Isaac Asimov or a Stephen King. By Philip Elmer-DeWitt. Reported by Jamie Murphy/Cambridge