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'{{refimprove|date=June 2011}} A '''machine-check exception''' ('''MCE''') is a type of [[computer hardware]] [[error]] that occurs when a [[computer]]'s [[central processing unit]] detects a hardware error in the processor itself, the memory, the [[Input/output|I/O]] devices, or on the system bus; in some architectures{{efn|On other architectures, an MCE may occur in order to log, e.g., a memory corrected by ECC.}}, an MCE only occurs for an unrecoverable error. On [[x86]] architectures, a machine-check exception is not caused by software. However, on other architectures such as [[PowerPC]], certain software bugs such as invalid memory accesses can cause machine-check exceptions. The error usually occurs due to component failure or the overheating or overclocking of hardware components. Most machine-check exceptions halt the operating system and require a restart before users can continue normal operation.{{dubious|linux restart|date=May 2020}} Diagnosing the failure can be often difficult because so little information about what caused the problem is captured during the error. Modern versions of [[Microsoft Windows]] on [[IA-32]] and [[x86-64]] processors handle machine-check exceptions through the [[Windows Hardware Error Architecture]]. When [[Windows Hardware Error Architecture|WHEA]] detects an uncorrectable machine check exception, it displays the error in a [[Blue Screen of Death]], with the following parameters (which vary, but the first parameter is always 0x0 for a machine check exception):<ref>{{cite web | url=https://docs.microsoft.com/en-us/windows-hardware/drivers/debugger/bug-check-0x124---whea-uncorrectable-error | title=Bug Check 0x124: WHEA_UNCORRECTABLE_ERROR | publisher=[[MSDN]] | date=2016-09-29 | accessdate=2017-07-13}}</ref> ''' *** STOP: 0x00000124 (0x0000000000000000, 0x0000000000000000, 0x0000000000000000, 0x0000000000000000) ''' Older versions of Windows handle similar exceptions through the [[Machine Check Architecture]]. In this case, the Blue Screen of Death will show an error similar to the following:<ref>{{cite web | url=https://support.microsoft.com/en-au/help/162363/understanding-and-troubleshooting-the-stop-0x0000009c-screen | title=Bug Check 0x9C: MACHINE_CHECK_EXCPETION | publisher=[[Microsoft Support]] | date=2018-03-31 | accessdate=2018-03-31}}</ref> ''' STOP: 0x0000009C (0x00000030, 0x00000002, 0x00000001, 0x80003CBA) ''' On [[Linux]], a process (such as <code>klogd</code><ref>{{cite web | url= https://linux.die.net/man/8/klogd | title= klogd(8) - Linux man page | author=Steve Lord, Greg Wettstein | quote=klogd is a system daemon which intercepts and logs Linux kernel messages. | accessdate=2017-07-13}}</ref>) writes a message to the kernel log and/or the console screen (usually only to the console when the error is non-recoverable and the machine crashes as a result): '''CPU 0: Machine Check Exception: 0000000000000004 Bank 2: f200200000000863 Kernel panic: CPU context corrupt''' ==Problem types== Most of these errors relate specifically to the [[Pentium (brand)|Pentium]] processor family. Similar errors may occur on other processors and will cause similar problems. Some of the main hardware problems that cause MCEs include: * [[System bus]] errors: (error communicating between the processor and the [[motherboard]]). * [[Random access memory|Memory]] errors: [[parity bit|parity checking]] detects when a memory error has occurred. [[Error correction code]] (ECC) can correct limited memory errors so that processing can continue. * [[CPU cache]] errors in the processor. ==Possible causes== Machine checks are a hardware problem, not a software problem. They are often the result of [[overclocking]] or overheating. In some cases, the microprocessor will enter thermal shutdown when its temperature exceeds a defined limit, a behavior intended to avoid permanent damage. Machine checks may be caused by bus errors introduced by other components, such as memory and/or I/O devices. Possible causes include: * Inadequate microprocessor cooling due to a [[Computer cooling|CPU heatsink]] and/or [[Computer fan|case fans]] (or filters) clogged with dust or detached from mountings. * [[Overclocking]] the system beyond the maximum speed at which the microprocessor is capable of operating. * Failing mainboard component, or physical damage to the mainboard, such as a fractured trace. * Failing microprocessor. * Failing memory. * Failing I/O controllers, on either the mainboard or on accessory cards. * Failing I/O devices, such as disk drives. * Inadequate or failing power supply. Cooling problems are usually obvious upon inspection. A failing mainboard or microprocessor usually can be identified by swapping them with parts known to be good. Memory can be checked by booting to a diagnostic tool, such as [[memtest86]]. Non-essential failing I/O devices and controllers can be identified by unplugging them if possible or disabling them to see if the problem disappears. If the failures typically only occur fairly soon after the OS is booted or not at all or not for days, it may be suggestive of a power supply issue. With a power supply problem, the failure often occurs when power demand peaks as the OS starts up any external devices for use. ==Decoding MCEs== For IA-32 and Intel 64 processors, consult the Intel 64 and IA-32 Architectures Software Developer's Manual<ref>{{cite book | title = Intel® 64 and IA-32 Architectures Software Developer's Manual Volume 3B: System Programming Guide, Part 2 | publisher = [[Intel]] Corporation | date = November 2018 | chapter = Machine Check Architecture | chapter-url = https://software.intel.com/en-us/download/intel-64-and-ia-32-architectures-sdm-volume-3b-system-programming-guide-part-2}}</ref> Chapter 15 (Machine-Check Architecture), or the Microsoft KB Article on Windows Exceptions.<ref>{{cite web | url=https://support.microsoft.com/en-us/kb/329284 | title=Stop error message in Windows XP that you may receive: "0x0000009C (0x00000004, 0x00000000, 0xb2000000, 0x00020151)" | publisher=[[MSDN]] | date=2015-12-07 | accessdate=2017-07-13}}</ref> ===Programs to decode Intel and AMD MCEs=== * mcat: A Windows command-line program from [[AMD]] to decode MCEs from [[AMD K8]], Family [[AMD K10|0x10]] and [[AMD K11|0x11]] processors. * mcelog<ref>{{cite web | url=http://www.mcelog.org/ | title=mcelog: Advanced hardware error handling for x86 Linux | date=2015-04-20 | accessdate=2017-07-13}}</ref> A [[Linux]] daemon by Andi Kleen to handle MCEs for modern x86 processors. mcelog can also decode machine checks. * parsemce<ref>{{cite web | url=https://www.kernel.org/pub/linux/kernel/people/davej/tools/parsemce.c | title=parsemce: Linux Machine check exception handler parser. | date=2003-07-22 | accessdate=2017-07-13}}</ref> a [[Linux]] program by Dave Jones to decode MCEs from [[AMD K7]] processors. * mced<ref>{{Github|thockin/mcedaemon}}</ref> a [[Linux]] program by Tim Hockin to gather MCEs from the kernel and alert interested applications. Note that it does not try to interpret the MCE data, it simply alerts other programs. ==See also== *[[Machine check architecture]] *[[Blue screen of death]] *[[Kernel panic]] ==Notes== {{Notelist}} ==References == {{Reflist|35em}} ==External links== * [http://www.mcelog.org mcelog: Advanced hardware error handling for x86 Linux] * [https://www.kernel.org/pub/linux/kernel/people/davej/tools/parsemce.c parsemce: Linux Machine check exception handler parser] [[Category:Computer errors]] {{compu-hardware-stub}}'