GoKawiilReverse-engineering the 1998 Ultima Online demo server
May 1, 2026
After 10 years of on-and-off work, I’m releasing a full reverse-engineering of the 1998 Ultima Online demo server: https://github.com/draxinar/ouo. About 5,000 functions disassembled from MSVC x86 and translated into portable C99, with each function compared instruction-by-instruction against the binary.
UoDemo.exe
For those who don’t know, Ultima Online is a 1997 MMORPG developed by Origin Systems Inc. It was one of the first commercially successful MMORPGs. The client ran on Windows and each server (so called “shards”) ran on multiple Solaris machines (the map was split by regions).
The first release of “Ultima Online: The Second Age” expansion (October 1998) shipped with a standalone Ultima Online demo ( UoDemo.exe and UoDemo.dat ), which bundled a client and a Windows port of the full server code and data. UoDemo.exe is dated 1998-09-02, and the server data were extracted from the production server on June 2nd, 1998. A handful of features were stubbed for the demo and the playable map was reduced to the island of Ocllo (a small NPC town off the southern coast of Britannia), but the rest is the actual production server code that was running on live UO in mid-1998. The demo featured a simple quest to kill a dragon on the island of Ocllo, with an overview of the basic game mechanisms (speech, trading, combat, etc.). Many UO server emulators reused parts of it, but so far none have ever fully reverse-engineered it.
UoDemo.exe was compiled with Microsoft Visual C++ 5.0 (Visual Studio 97), targeting a pre-C++98 dialect of C++.
I worked on this project intermittently for 10 years, until recent developments in LLMs finally made it possible to complete this seemingly never-ending task.
Methodology
Disassembly with radare2.
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