in a sane OS? Nothing until you run out of ram. In a Microsoft OS? Depends on the app -- some are dependent (many games) on having swap available (and may err

in a sane OS? Nothing until you run out of ram. In a Microsoft OS? Depends on the app -- some are dependent (many games) on having swap available (and may err silently or under false pretenses without one). I've found that a lot of MMO style games include cheat detection systems (see : rootkit) that rely on swap, and fail without it. As to why they do that, i'm unsure.