Well first of all, lets assume you use windows XP for your computer.
XP uses between 300 and 500 MB of ram to itself depending on what programs and services you run in the background.
Now based on Dark Warriors info that a realmap uses 1GB of ram, that would leave you with -500MB ram, which means the computer would start using the harddrive (virtual memory) instead of ram.
And now im assuming that you got only 1 harddrive, and have the server-files and virtual-memory is on the same harddrive, then you will have serious lag even with 1 player, since not only is the harddrive thousands of times slower than your RAM but the harddrive would also loose read speed/access time due to beeing read from by 2 separate sources (and perhaps even more), making it even slower.
And if you also USE the same computer for hosting AND daily use such as surfing, tibia-client and whatnot, then that will cause even MORE seveer lag.
The best solution is to either get more ram, or use a smaller map.
