The software that powered the simulation, Halliday’s new OASIS Reality Engine, also represented a huge technological breakthrough. It managed to overcome limitations that had plagued previous simulated realities. In addition to restricting the overall size of their virtual environments, earlier MMOs had been forced to limit their virtual populations, usually to a few thousand users per server. If too many people were logged in at the same time, the simulation would slow to a crawl and avatars would freeze in midstride as the system struggled to keep up. But the OASIS utilized a new kind of fault-tolerant server array that could draw additional processing power from every computer connected to it. At the time of its initial launch, the OASIS could handle up to five million simultaneous users, with no discernible latency and no chance of a system crash.