Tony wrote: Compressed, rather then encrypted, although I'm sure the resulting obfuscation was considered a benefit by the designers. And it wasn't just strings that were read from the disk; the actual game was written in Z-code, the instruction set for a virtual machine. The only Z-80 code was the Z-code interpreter, which implemented a virtual memory system in order to make Zork playable on a 32K machine. The general principles were described in the article "How to Fit a Large Program Into a Small Machine, or How to Fit the Great Underground Empire on Your Desk-top", by Mark Blank and Stu Galley, published in Creative Computing in July 1980. The article may be found at http://www.csd.uwo.ca/~pete/Infocom/Articles/small.html