A stop error, better known as a Blue Screen of Death (also known as a blue screen or BSoD), is an error screen displayed on a Windows computer system after a fatal system error, also known as a system crash: when the operating system reaches a condition where it can no longer operate safely.
BSoDs have been around since the first Windows edition, Windows 1.01. It appears as a blue screen with white letters telling of a problem. BSoDs have been present in Windows NT 3.1 (the first version of the Windows NT family, released in 1993) and all Windows operating systems released afterwards. BSoDs can be caused by poorly written device drivers or malfunctioning hardware, such as faulty memory, power supply issues, overheating of components, or hardware running beyond its specification limits. In the Windows 9x era, incompatible DLLs or bugs in the operating system kernel could also cause BSoDs. Because of the instability and lack of memory protection in Windows 9x, BSoDs were much more common.