<P> In Windows NT family of operating systems, the blue screen of death (officially known as a stop error and referred to as "bug check" in the Windows software development kit and driver development kit documentation) occurs when the kernel or a driver running in kernel mode encounters an error from which it cannot recover . This is usually caused by an illegal operation being performed . The only safe action the operating system can take in this situation is to restart the computer . As a result, data may be lost, as users are not given an opportunity to save data that has not yet been saved to the hard drive . </P> <P> The text on the error screen contains the code of the error and its symbolic name (e.g. "0x0000001E, KMODE_EXCEPTION_NOT_HANDLED") along with four error - dependent values in parentheses that are there to help software engineers fix the problem that occurred . Depending on the error code, it may display the address where the problem occurred, along with the driver which is loaded at that address . Under Windows NT, the second and third sections of the screen may contain information on all loaded drivers and a stack dump, respectively . The driver information is in three columns; the first lists the base address of the driver, the second lists the driver's creation date (as a Unix timestamp), and the third lists the name of the driver . </P> <P> By default, Windows will create a memory dump file when a stop error occurs . Depending on the OS version, there may be several formats this can be saved in, ranging from a 64kB "minidump" (introduced in Windows 2000) to a "complete dump" which is effectively a copy of the entire contents of physical memory (RAM). The resulting memory dump file may be debugged later, using a kernel debugger . For Windows WinDBG or KD debuggers from Debugging Tools for Windows are used . A debugger is necessary to obtain a stack trace, and may be required to ascertain the true cause of the problem; as the information on - screen is limited and thus possibly misleading, it may hide the true source of the error . By default, Windows XP is configured to save only a 64kB minidump when it encounters a stop error, and to then automatically reboot the computer . Because this process happens very quickly, the blue screen may be seen only for an instant or not at all . Users have sometimes noted this as a random reboot rather than a traditional stop error, and are only aware of an issue after Windows reboots and displays a notification that it has recovered from a serious error . This happens only when the computer has a function called "Auto Restart" enabled, which can be disabled in the Control Panel which in turn shows the stop error . </P> <P> Microsoft Windows can also be configured to send live debugging information to a kernel debugger running on a separate computer . If a stop error is encountered while a live kernel debugger is attached to the system, Windows will halt execution and cause the debugger to break in, rather than displaying the BSoD . The debugger can then be used to examine the contents of memory and determine the source of the problem . </P>

What is the reason for blue screen error