Minecraft wiki entry for Crash, associated text: JVM Crashes are crashes where the Java Virtual Machine, the program that runs Minecraft itself, crashes. These are almost always caused by doing large, potentially groundbreaking operations like moving many blocks, exploding a lot of TNT, or other memory or processor intensive activities, and additionally almost always are caused by running out of RAM. These are unique in that the crash message is quite different, having come from the JVM's crash handler rather than Minecraft's handler. Because of this, they do not generate a crash report in the .minecraft/crash-reports directly, but rather one directly in the .minecraft folder, with name "hs_err_pid<PID>.log" where <PID> is the Process ID of the JVM at that time. Additionally, these crashes cannot be stopped by mods that "catch" Minecraft crashes, like VanillaFix.