A fatal system error, also known as a system crash, stop error, kernel error, or bug check, is when an operating system halts at the moment it reaches a condition where it can no longer operate safely. In Microsoft Windows, a fatal system error can be deliberately caused from a kernel-mode driver with either the KeBugCheck or KeBugCheckEx function. However, this should only be done as a last option when a critical driver is corrupted and is impossible to recover. This design parallels that in OpenVMS. The Unix kernel panic concept is very similar.