====================			= MemTest-86 v3.2  =			=   Nov 11, 2004   =			=   Chris Brady    =			====================Table of Contents=================  1) Introduction  2) Licensing  3) Installation  4) Serial Port Console  5) Online Commands  6) Memory Sizing  7) Error Display  8) Trouble-shooting Memory Errors  9) Execution Time 10) Memory Testing Philosophy 11) Memtest86 Test Algorithms 12) Individual Test Descriptions 13) Problem Reporting - Contact Information 14) Known Problems 15) Planned Features List 16) Change Log 17) Donations 18) Acknowledgments1) Introduction===============Memtest86 is thorough, stand alone memory test for Intel/AMD x86 architecturesystems.  BIOS based memory tests are only a quick check and often missfailures that are detected by Memtest86.For updates go to the Memtest86 web page:	http://www.memtest86.com2) Licensing============Memtest86 is released under the terms of the Gnu Public License (GPL). Otherthan the provisions of the GPL there are no restrictions for use, private orcommercial.  See: http://www.gnu.org/licenses/gpl.html for details.Explicit permission for inclusion of Memtest86 in software compilations andpublications is hereby granted.3) Installation (Linux Only)============================Memtest86 is a stand alone program and can be loaded from either a diskpartition or from a floppy disk.To build Memtest86:   1) Review the Makefile and adjust options as needed.   2) Type "make"This creates a file named "memtest.bin" which is a bootable image.  Thisimage file may be copied to a floppy disk or lilo may be used to boot thisimage from a hard disk partition.To create a Memtest86 bootdisk   1) Insert a blank write enabled floppy disk.   2) As root, Type "make install"To boot from a disk partition via lilo   1) Copy the image file to a permanent location (ie. /memtest).   2) Add an entry in the lilo config file (usually /etc/lilo.conf) to boot      memtest86.  Only the image and label fields need to be specified.       The following is a sample lilo entry for booting memtest86:	image = /memtest	label = memtest   3) As root,  type "lilo"      At the lilo prompt enter memtest to boot memtest86.If you encounter build problems a binary image has been included (precomp.bin).To create a boot-disk with this pre-built image do the following:   1) Insert a blank write enabled floppy disk.   2) Type "make install-precomp"4) Serial Console=================Memtest86 can be used on PC's equipped with a serial port for the console.By default serial port console support is not enabled since it slowsdown testing.  To enable change the SERIAL_CONSOLE_DEFAULT define inconfig.h from a zero to a one.  The serial console baud rate may alsobe set in config.h with the SERIAL_BAUD_RATE define.  The other serialport settings are no parity, 8 data bits, 1 stop bit.  All of the featuresused by memtest86 are accessible via the serial console.  However, thescreen sometimes is garbled when the online commands are used.5) Online Commands==================Memtest86 has a limited number of online commands.  Online commandsprovide control over caching, test selection, address range and errorscrolling.  A help bar is displayed at the bottom of the screen listingthe available on-line commands.   Command  Description  ESC   Exits the test and does a warm restart via the BIOS.  c     Enters test configuration menu	    Menu options are:               1) Cache mode               2) Test selection	       3) Address Range	       4) Memory Sizing	       5) Error Summary	       6) Error Report Mode 	       7) ECC Mode	       8) Restart 	       9) Adv. Options  SP    Set scroll lock (Stops scrolling of error messages)	Note: Testing is stalled when the scroll lock is	set and the scroll region is full.  CR    Clear scroll lock (Enables error message scrolling)6) Memory Sizing================The BIOS in modern PC's will often reserve several sections of memory forit's use and also to communicate information to the operating system (ie.ACPI tables).  It is just as important to test these reserved memory blocksas it is for the remainder of memory.  For proper operation all of memoryneeds to function properly regardless of what the eventual use is.  Forthis reason Memtest86 has been designed to test as much memory as ispossible. However, safely and reliably detecting all of the available memory has beenproblematic.  Versions of Memtest86 prior to v2.9 would probe to find wherememory is. This works for the vast majority of motherboards but is not 100%reliable. Sometimes the memory size is incorrect and worse probing the wrongplaces can in some cases cause the test to hang or crash.  Starting in version 2.9 alternative methods are available for determining thememory size. By default the test attempts to get the memory size from theBIOS using the "e820" method.  With "e820" the BIOS provides a table of memorysegments and identifies what they will be used for.  By default Memtest86will test all of the ram marked as available and also the area reserved forthe ACPI tables.  This is safe since the test does not use the ACPI tablesand the "e820" specifications state that this memory may be reused after thetables have been copied.  Although this is a safe default some memory willnot be tested.Two additional options are available through online configuration options.The first option (BIOS-All) also uses the "e820" method to obtain a memorymap.  However, when this option is selected all of the reserved memorysegments are tested, regardless of what their intended use is.  The onlyexception is memory segments that begin above 3gb.  Testing has shown thatthese segments are typically not safe to test.  The BIOS-All option is morethorough but could be unstable with some motherboards.The second option for memory sizing is the traditional "Probe" method.This is a very thorough but not entirely safe method.  In the majority ofcases the BIOS-All and Probe methods will return the same memory map.For older BIOS's that do not support the "e820" method there are twoadditional methods (e801 and e88) for getting the memory size from theBIOS.  These methods only provide the amount of extended memory that isavailable, not a memory table.  When the e801 and e88 methods are usedthe BIOS-All option will not be available.The MemMap field on the display shows what memory size method is in use.Also the RsvdMem field shows how much memory is reserved and is not beingtested.7) Error Information======================Memtest has two options for reporting errors.  The default is to reportindividual errors.  In BadRAM Patterns mode patterns are created foruse with the Linux BadRAM feature.  This slick feature allows Linux toavoid bad memory pages.  Details about the BadRAM feature can be found at:	http://home.zonnet.nl/vanrein/badramFor individual errors the following information is displayed when a memoryerror is detected.  An error message is only displayed for errors with adifferent address or failing bit pattern.  All displayed values are inhexadecimal.  Tst:			Test number  Failing Address :	Failing memory address   Good:			Expected data pattern   Bad:			Failing data pattern   Err-Bits:		Exclusive or of good and bad data (this shows the			position of the failing bit(s))  Count:		Number of consecutive errors with the same address			and failing bitsIn BadRAM Patterns mode, Lines are printed in a form badram=F1,M1,F2,M2.In each F/M pair, the F represents a fault address, and the corresponding Mis a bitmask for that address. These patterns state that faults haveoccurred in addresses that equal F on all "1" bits in M. Such a pattern maycapture more errors that actually exist, but at least all the errors arecaptured. These patterns have been designed to capture regular patterns oferrors caused by the hardware structure in a terse syntax.The BadRAM patterns are `grown' increment-ally rather than `designed' from anoverview of all errors. The number of pairs is constrained to five for anumber of practical reasons. As a result, handcrafting patterns from theoutput in address printing mode may, in exceptional cases, yield betterresults.8) Trouble-shooting Memory Errors================================Please be aware that not all errors reported by Memtest86 are due tobad memory. The test implicitly tests the CPU, L1 and L2 caches as well asthe motherboard.  It is impossible for the test to determine what causesthe failure to occur.  Most failures will be due to a problem with memory.When it is not, the only option is to replace parts until the failure iscorrected.  Once a memory error has been detected, determining the failingmodule is not a clear cut procedure.  With the large number of motherboardvendors and possible combinations of simm slots it would be difficult ifnot impossible to assemble complete information about how a particularerror would map to a failing memory module.  However, there are stepsthat may be taken to determine the failing module.  Here are threetechniques that you may wish to use:1) Removing modulesThis is simplest method for isolating a failing modules, but may only beemployed when one or more modules can be removed from the system.  Byselectively removing modules from the system and then running the testyou will be able to find the bad module(s).  Be sure to note exactly whichmodules are in the system when the test passes and when the test fails.2) Rotating modulesWhen none of the modules can be removed then you may wish to rotate modulesto find the failing one.  This technique can only be used if there arethree or more modules in the system.  Change the location of two modulesat a time.  For example put the module from slot 1 into slot 2 and putthe module from slot 2 in slot 1.  Run the test and if either the failingbit or address changes then you know that the failing module is one of theones just moved. By using several combinations of module movement youshould be able to determine which module is failing.3) Replacing modulesIf you are unable to use either of the previous techniques then you areleft to selective replacement of modules to find the failure.  4) Avoiding allocationThe printing mode for BadRAM patterns is intended to construct boot timeparameters for a Linux kernel that is compiled with BadRAM support. Thiswork-around makes it possible for Linux to reliably run on defectiveRAM.  For more information on BadRAM supportfor Linux, sail to       http://home.zonnet.nl/vanrein/badramSometimes memory errors show up due to component incompatibility.  A memorymodule may work fine in one system and not in another.  This is notuncommon and is a source of confusion.  The components are not necessarilybad but certain combinations may need to be avoided.I am often asked about the reliability of errors reported by Mestest86.In the vast majority of cases errors reported by the test are valid.There are some systems that cause Memtest86 to be confused about the size ofmemory and it will try to test non-existent memory.  This will cause a largenumber of consecutive addresses to be reported as bad and generally therewill be many bits in error.  If you have a relatively small number offailing addresses and only one or two bits in error you can be certainthat the errors are valid.  Also intermittent errors are always valid.All valid memory errors should be corrected.  It is possible that aparticular error will never show up in normal operation. However, operatingwith marginal memory is risky and can result in data loss and evendisk corruption.  You can be sure that Murphy will get you if you knowabout a memory error and ignore it.Memtest86 can not diagnose many types of PC failures.  For example afaulty CPU that causes Windows to crash will most likely just causeMemtest86 to crash in the same way.