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https://github.com/memtest86plus/memtest86plus

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README 

        
# Memtest86+



Memtest86+ is a free, open-source, stand-alone memory tester for x86 and

x86-64 architecture computers. It provides a much more thorough memory

check than that provided by BIOS memory tests.



It is also able to access almost all the computer's memory, not being

restricted by the memory used by the operating system and not depending

on any underlying software like UEFI libraries.



Memtest86+ can be loaded and run either directly by a PC BIOS (legacy or UEFI)

or via an intermediate bootloader that supports the Linux 16-bit, 32-bit,

64-bit, or EFI handover boot protocol. It should work on any Pentium class or

later 32-bit or 64-bit CPU.



Binary releases (both stable and nightly dev builds) are available on

[memtest.org](https://memtest.org).



## Table of Contents



  * [Origins](#origins)

  * [Licensing](#licensing)

  * [Build and Installation](#build-and-installation)

  * [Boot Options](#boot-options)

  * [Keyboard Selection](#keyboard-selection)

  * [Operation](#operation)

  * [Error Display](#error-reporting)

  * [Trouble-shooting Memory Errors](#trouble-shooting-memory-errors)

  * [Execution Time](#execution-time)

  * [Memtest86+ Test Algorithms](#memory-testing-philosophy)

  * [Individual Test Descriptions](#individual-test-descriptions)

  * [Known Limitations and Bugs](#known-limitations-and-bugs)

  * [Code Contributions](#code-contributions)

  * [Acknowledgments](#acknowledgments)



## Origins



Memtest86+ v6.00 was based on PCMemTest, which was a fork and rewrite of the

earlier Memtest86+ v5, which in turn was a fork of MemTest-86. The purpose

of the PCMemTest rewrite was to:



  * make the code more readable and easier to maintain

  * make the code 64-bit clean and support UEFI boot

  * fix failures seen when building with newer versions of GCC



In the process of creating PCMemTest, a number of features of Memtest86+ v5

that were not strictly required for testing the system memory were dropped. In

particular, no attempt was made to measure the cache and main memory speed, or

to identify and report the DRAM type. These features were added back and expanded

in Memtest86+ v6.0 to create a unified, fully-featured release.



## Licensing



Memtest86+ is released under the terms of the GNU General Public License

version 2 (GPLv2). Other than the provisions of the GPL there are no

restrictions for use, private or commercial. See the LICENSE file for details.



## Build and Installation



Build is only tested on a Linux system, but should be possible on any system

using the GNU toolchain and the ELF file format. The tools required are:



  * GCC

  * binutils

  * make

  * dosfstools and mtools (optional)

  * xorrisofs (optional)



To build a 32-bit image, change directory into the `build32` directory and

type `make`. The result is a `memtest.bin` binary image file which can be

booted directly by a legacy BIOS (in floppy mode) or by an intermediate

bootloader using the Linux 16-bit boot protocol and a `memtest.efi` binary

image file which can be booted directly by a 32-bit UEFI BIOS. Either image

can be booted by an intermediate bootloader using the Linux 32-bit or 32-bit

EFI handover boot protocols.



To build a 64-bit image, change directory into the `build64` directory and

type `make`. The result is a `memtest.bin` binary image file which can be

booted directly by a legacy BIOS (in floppy mode) or by an intermediate

bootloader using the Linux 16-bit boot protocol and a `memtest.efi` binary

image file which can be booted directly by a 64-bit UEFI BIOS. Either image

can be booted by an intermediate bootloader using the Linux 32-bit, 64-bit,

or 64-bit EFI handover boot protocols.



In either case, to build an ISO image that can be used to create a bootable

CD, DVD, or USB Flash drive, type `make iso`, The result is a `memtest.iso`

ISO image file. This can then be written directly to a blank CD or DVD, or

to a USB Flash drive, which can then be booted directly by a legacy or UEFI

PC BIOS.



Note that when writing to a USB Flash drive, the ISO image must be written

directly ('dumped') to the raw device, either by using the `dd` command or

by using a utility that provides the same functionality.



When using an intermediate bootloader, either the `memtest.bin` file or the

`memtest.efi` file should be stored in a disk partition the bootloader can

access, and the bootloader configuration should be updated to boot from

that file as if it were a Linux kernel with no initial RAM disk. Several

boot command line options are recognised, as described below. If using the

16-bit boot protocol, Memtest86+ will use the display in text mode (640x400).

If using the 32-bit or 64-bit boot protocols, Memtest86+ will use the display

in either text mode or graphics mode, as specified in the `boot_params` struct

passed to it by the bootloader. If in graphics mode, the supplied framebuffer

must be at least 640x400 pixels; if larger, the display will be centred. If

the system was booted in UEFI mode, graphics mode must be used.



For test purposes, there is also an option to build an ISO image that uses

GRUB as an intermediate bootloader. See the `Makefile` in the `build32` or

`build64` directory for details. The ISO image is both legacy and UEFI

bootable, so you need GRUB modules for both legacy and EFI boot installed

on your build system (e.g. on Debian, the required GRUB modules are located

in packages `grub-pc-bin`, `grub-efi-ia32-bin` and `grub-efi-amd64-bin`).

You may need to adjust some path and file names in the Makefile to match

the naming on your system.



The GRUB configuration files contained in the `grub` directory are there for

use on the test ISO, but also serve as an example of how to boot Memtest86+

from GRUB.



## Boot Options



An intermediate bootloader may pass a boot command line to Memtest86+. The

command line may contain one or more options, separated by spaces. Each

option consists of an option name, optionally followed by an `=` sign and

one or more parameters, separated by commas. The following options are

recognised:



  * nosmp

    * disables ACPI table parsing and the use of multiple CPU cores

  * nobench

    * disables the integrated memory benchmark

  * nobigstatus

    * disables the big PASS/FAIL pop-up status display

  * nosm

    * disables SMBUS/SPD parsing, DMI decoding and memory benchmark

  * nomch

    * disables memory controller configuration polling

  * nopause

    * skips the pause for configuration at startup

  * keyboard=*type*

    * where *type* is one of

      * legacy

      * usb

      * both

  * screen.mode=*w*x*h* (EFI framebuffer only)

    * where *w*x*h* is the preferred screen resolution (e.g. 1024x768)

  * screen.mode=bios (EFI framebuffer only)

    * uses the default screen resolution set by the UEFI BIOS

  * screen.rhs-up (graphics mode only)

    * rotates the display clockwise by 90 degrees

  * screen.lhs-up (graphics mode only)

    * rotates the display anti-clockwise by 90 degrees

  * efidebug

    * displays information about the EFI framebuffer

  * usbdebug

    * pauses after probing for USB keyboards

  * usbinit=*mode*

    * where *mode* is one of

      * 1 = use the two-step init sequence for high speed devices

      * 2 = add a second USB reset in the init sequence

      * 3 = the combination of modes 1 and 2

  * console=ttyS*x*,*y*

    * activate serial/tty console output, where *x* is one of the following IO port

      *  0 = 0x3F8

      *  1 = 0x2F8

      *  2 = 0x3E8

      *  3 = 0x2E8

    * and *y* is an optional baud rate to choose from the following list

      * 9600

      * 19200

      * 38400

      * 57600

      * 115200 (default if not specified or invalid)

      * 230400

  * console=*x*,*y*

    * activate MMIO UART console, where *x* is the MMIO stride (reg. width)

      * mmio   = 8-bit MMIO

      * mmio16 = 16-bit MMIO

      * mmio32 = 32-bit MMIO

    * and *y* is the MMIO address in hex. with `0x` prefix (eg: 0xFEDC9000)



## Keyboard Selection



Memtest86+ supports both the legacy keyboard interface (using I/O ports 0x60

and 0x64) and USB keyboards (using its own USB device drivers). One or the

other or both can be selected via the boot command line, If not specified on

the command line, the default is to use both if the system was booted in UEFI

mode, otherwise to only use the legacy interface.



Older BIOSs usually support USB legacy keyboard emulation, which makes USB

keyboards act like legacy keyboards connected to ports 0x60 and 0x64. This

can often be enabled or disabled in the BIOS setup menus. If Memtest86+'s

USB device drivers are enabled, they will override this and access any USB

keyboards directly. The downside of that is that the USB controllers and

device drivers require some memory to be reserved for their private use,

which means that memory can't then be covered by the memory tests. So to

maximise test coverage, if it is supported, enable USB legacy keyboard

emulation and, if booting in UEFI mode, add `keyboard=legacy` on the boot

command line.



**NOTE**: Some UEFI BIOSs only support USB legacy keyboard emulation when

you enable the Compatibility System Module (CSM) in the BIOS setup. Others

only support it when actually booting in legacy mode.



Many USB devices don't fully conform to the USB specification. If the USB

keyboard probe hangs or fails to detect your keyboard, try the various

workarounds provided by the "usbinit" boot option.



**NOTE**: Hot-plugging is not currently supported by the Memtest86+ USB

drivers. When using these, your USB keyboard should be plugged in before

running Memtest86+ and should remain plugged in throughout the test.



## Display Rotation



Some 2-in-1 machines use an LCD panel which is natively a portrait mode

display but is mounted on its side when attached to the keyboard. When

using the display in graphics mode, Memtest86+ can rotate its display

to match. Add either the "screen.rhs-up" or the "screen.lhs-up" option

on the boot command line, depending on the orientation of the LCD panel.

When using the display in text mode, it is expected that the BIOS will

take care of this automatically.



## Screen Resolution



When booted in legacy mode, Memtest86+ will use the screen resolution that

has been set by the BIOS or by the intermediate bootloader. When booted in

UEFI mode, Memtest86+ will normally select the smallest available screen

resolution that encompasses its 640x400 pixel display. Some BIOSs return

incorrect information about the available display modes, so you can

override this by adding the "screen.mode=" option on the boot command

line.



Note that when using display rotation, the specified screen resolution is

for the unrotated display.



## Operation



Once booted, Memtest86+ will initialise its display, then pause for a few

seconds to allow the user to configure its operation. If no key is pressed,

it will automatically start running all tests using a single CPU core,

continuing indefinitely until the user reboots or halts the machine.



At startup, and when running tests, Memtest86+ responds to the following keys:



  * F1

    * enters the configuration menu

  * F2

    * toggles use of multiple CPU cores (SMP)

  * Space

    * toggles scroll lock (stops/starts error message scrolling)

  * Enter

    * single message scroll (only when scroll lock enabled)

  * Escape

    * exits the test and reboots the machine



Note that testing is stalled when scroll lock is enabled and the scroll region

is full.



The configuration menu allows the user to:



  * select which tests are run (default: all tests)

  * limit the address range over which tests are performed (default: all memory)

  * select the CPU sequencing mode (default: parallel)

    * parallel

      * each CPU core works in parallel on a subset of the memory region being

        tested

    * sequential

      * each CPU core works in turn on the full memory region being tested

    * round robin

      * a single CPU core works on the full memory region being tested, with a

        new CPU core being selected (in round-robin fashion) for each test

  * select the error reporting mode (default: individual errors)

    * error counts only

    * error summary

    * individual errors

    * BadRAM patterns

  * select which of the available CPU cores are used (at startup only)

    * a maximum of 256 CPU cores can be selected, due to memory and

      display limits

    * the bootstrap processor (BSP) cannot be deselected

  * enable or disable the temperature display (at startup only)

  * enable or disable boot tracing for debug (at startup only)

  * skip to the next test (when running tests)



In all cases, the number keys may be used as alternatives to the function keys

(1 = F1, 2 = F2, ... 0 = F10).



## Error Reporting



The error reporting mode may be changed at any time without disrupting the

current test sequence. Error statistics are collected regardless of the

current error reporting mode (so switching to error summary mode will show

the accumulated statistics since the current test sequence started). BadRAM

patterns are only accumulated when in BadRAM mode.



Any change to the selected tests, address range, or CPU sequencing mode will

start a new test sequence and reset the error statistics.



### Error Counts Only



The error counts only mode just displays the total number of errors found since

the current test sequence started.



### Error Summary



The error summary mode displays the following information:



  * Lowest Error Address

    * the lowest address that where an error has been reported

  * Highest Error Address

    * the highest address that where an error has been reported

  * Bits in Error Mask

    * a hexadecimal mask of all bits that have been in error

  * Bits in Error

    * total bits in error for all error instances and the min, max and average

      number of bits in error across each error instance

  * Max Contiguous Errors

    * the maximum of contiguous addresses with errors

  * Test Errors

     * the total number of errors for each individual test



### Individual Errors



The individual error mode displays the following information for each error

instance:



  * pCPU

    * the physical CPU core number that detected the error

  * Pass

    * the test pass number where the error occurred (a test pass is a single

      run over all the currently selected tests)

  * Test

    * the individual test number where the error occurred

  * Failing Address

    * the memory address where the error occurred

  * Expected

    * the hexadecimal data pattern expected to be found

  * Found

    * the hexadecimal data pattern read from the failing address

  * Err Bits (only in 32-bit builds)

    * a hexadecimal mask showing the bits in error



### BadRAM Patterns



The BadRAM patterns mode accumulates and displays error patterns for use with

the [Linux BadRAM feature](http://rick.vanrein.org/linux/badram/). Lines are

printed in the form `badram=F1,M1,F2,M2...` In each `F,M` pair, the `F`

represents a fault address and the `M` is a bitmask for that address. These

patterns state that faults have occurred in addresses that equal F on all `1`

bits in M. Such a pattern may capture more errors that actually exist, but

at least all the errors are captured. These patterns have been designed to

capture regular patterns of errors caused by the hardware structure in a terse

syntax.



The BadRAM patterns are grown incrementally rather than calculated from an

overview of all errors. The number of pairs is constrained to ten for a

number of practical reasons. As a result, handcrafting patterns from the

output in address printing mode may, in exceptional cases, yield better

results.



**NOTE** As mentioned in the individual test descriptions, the walking-ones

address test (test 0) and the block move test (test 7) do not contribute to

the BadRAM patterns as these tests do not allow the exact address of the

fault to be determined.



## Trouble-shooting Memory Errors



Please be aware that not all errors reported by Memtest86+ are due to bad

memory. The test implicitly tests the CPU, caches, and motherboard. It is

impossible for the test to determine what causes the 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 is corrected.



Once a memory error has been detected, determining the failing module is not a

clear cut procedure. With the large number of motherboard vendors and possible

combinations of memory slots it would be difficult if not impossible to assemble

complete information about how a particular error would map to a failing memory

module. However, there are steps that may be taken to determine the failing

module. Here are some techniques that you may wish to use:



* Removing modules

  * This is the simplest method for isolating a failing modules, but may only

    be employed when one or more modules can be removed from the system. By

    selectively removing modules from the system and then running the test

    you will be able to find the bad module(s). Be sure to note exactly which

    modules are in the system when the test passes and when the test fails.



* Rotating modules

  * When none of the modules can be removed then you may wish to rotate modules

    to find the failing one. This technique can only be used if there are three

    or more modules in the system. Change the location of two modules at a time.

    For example put the module from slot 1 into slot 2 and put the module from

    slot 2 in slot 1. Run the test and if either the failing bit or address

    changes then you know that the failing module is one of the ones just moved.

    By using several combinations of module movement you should be able to

    determine which module is failing.



* Replacing modules

  * If you are unable to use either of the previous techniques then you are

    left to selective replacement of modules to find the failure.



Sometimes memory errors show up due to component incompatibility. A memory

module may work fine in one system and not in another. This is not uncommon

and is a source of confusion. The components are not necessarily bad but

certain combinations may need to be avoided.



In the vast majority of cases errors reported by Memtest86+ are valid. There

are some systems that cause Memtest86+ to be confused about the size of memory

and it will try to test non-existent memory. This will cause a large number of

consecutive addresses to be reported as bad and generally there will be many

bits in error. If you have a relatively small number of failing addresses and

only one or two bits in error you can be certain that the errors are valid.

Also intermittent errors are always valid.



All valid memory errors should be corrected. It is possible that a particular

error will never show up in normal operation. However, operating with marginal

memory is risky and can result in data loss and even disk corruption.



Memtest86+ can not diagnose many types of PC failures. For example a faulty CPU

that causes your OS to crash will most likely just cause Memtest86+ to crash in

the same way.



## Execution Time



The time required for a complete pass of Memtest86+ will vary greatly depending

on CPU speed, memory speed, and memory size. Memtest86+ executes indefinitely.

The pass counter increments each time that all of the selected tests have been

run. Generally a single pass is sufficient to catch all but the most obscure

errors. However, for complete confidence when intermittent errors are suspected

testing for a longer period is advised.



## Memory Testing Philosophy



There are many good approaches for testing memory. However, many tests simply

throw some patterns at memory without much thought or knowledge of memory

architecture or how errors can best be detected. This works fine for hard

memory failures but does little to find intermittent errors. BIOS based memory

tests are useless for finding intermittent memory errors.



Memory chips consist of a large array of tightly packed memory cells, one for

each bit of data. The vast majority of the intermittent failures are a result

of interaction between these memory cells. Often writing a memory cell can

cause one of the adjacent cells to be written with the same data. An effective

memory test attempts to test for this condition. Therefore, an ideal strategy

for testing memory would be the following:



  1. write a cell with a zero

  2. write all of the adjacent cells with a one, one or more times

  3. check that the first cell still has a zero



It should be obvious that this strategy requires an exact knowledge of how the

memory cells are laid out on the chip. In addition there is a never ending

number of possible chip layouts for different chip types and manufacturers

making this strategy impractical. However, there are testing algorithms that

can approximate this ideal strategy.



## Memtest86+ Test Algorithms



Memtest86+ uses two algorithms that provide a reasonable approximation of the

ideal test strategy above. The first of these strategies is called moving

inversions. The moving inversion tests work as follows:



  1. Fill memory with a pattern

  2. Starting at the lowest address

     1. check that the pattern has not changed

     2. write the pattern's complement

     3. increment the address

     4. repeat 2.1 to 2.3

  3. Starting at the highest address

     1. check that the pattern has not changed

     2. write the pattern's complement

     3. decrement the address

     4. repeat 3.1 to 3.3



This algorithm is a good approximation of an ideal memory test but there are

some limitations. Most high density chips today store data 4 to 16 bits wide.

With chips that are more than one bit wide it is impossible to selectively

read or write just one bit. This means that we cannot guarantee that all

adjacent cells have been tested for interaction. In this case the best we can

do is to use some patterns to ensure that all adjacent cells have at least

been written with all possible one and zero combinations.



It can also be seen that caching, buffering, and out of order execution will

interfere with the moving inversions algorithm and make it less effective.

It is possible to turn off caching but the memory buffering in new high

performance chips cannot be disabled. To address this limitation a new

algorithm called Modulo-20 was created. This algorithm is not affected by

caching or buffering. The algorithm works as follows:



  1. For starting offsets of 0 - 19 do

     1. write every 20th location with a pattern

     2. write all other locations with the pattern's complement

     3. repeat 1.2 one or more times

     4. check every 20th location for the pattern



This algorithm accomplishes nearly the same level of adjacency testing as

moving inversions but is not affected by caching or buffering. Since separate

write passes (1.1, 1.2) and the read pass (1.4) are done for all of memory we

can be assured that all of the buffers and cache have been flushed between

passes. The selection of 20 as the stride size was somewhat arbitrary. Larger

strides may be more effective but would take longer to execute. The choice of

20 seemed to be a reasonable compromise between speed and thoroughness.



## Individual Test Descriptions



Memtest86+ executes a series of numbered tests to check for errors. These tests

consist of a combination of test algorithm, data pattern and caching. The

execution order for these tests were arranged so that errors will be detected

as rapidly as possible. A description of each test follows.



To allow testing of more than 4GB of memory on 32-bit CPUs, the physical

address range is split into 1GB windows which are be mapped one at a time

into a virtual memory window. Each 1GB window may contain one or more

contiguous memory regions. For most tests, the test is performed on each

memory region in turn. Caching is enabled for all but the first test.



### Test 0 : Address test, walking ones, no cache



In each memory region in turn, tests all address bits by using a walking

ones address pattern. Errors from this test are not used to calculate BadRAM

patterns.



### Test 1 : Address test, own address in window



In each memory region in turn, each address is written with its own address

and then each address is checked for consistency. This test is performed

sequentially with each available CPU, regardless of the CPU sequencing mode

selected by the user.



### Test 2 : Address test, own address + window



Across all memory regions, each address is written with its own virtual

address plus the window number (for 32-bit images) or own physical address

(for 64-bit images) and then each address is checked for consistency. This

catches any errors in the high order address bits that would be missed when

testing each window in turn. This test is performed sequentially with each

available CPU, regardless of the CPU sequencing mode selected by the user.



### Test 3 : Moving inversions, ones & zeros



In each memory region in turn, and for each pattern in turn, uses the moving

inversions algorithm with patterns of all ones and all zeros.



### Test 4 : Moving inversions, 8 bit pattern



In each memory region in turn, and for each pattern in turn, uses the moving

inversions algorithm with patterns of 8-bit wide walking ones and walking zeros.



### Test 5 : Moving inversions, random pattern



In each memory region in turn, and for each pattern in turn, uses the moving

inversions algorithm with patterns of a random number and its complement. The

random number is different on each test pass so multiple passes increase

effectiveness.



### Test 6 : Moving inversions, 32/64 bit pattern



In each memory region in turn, and for each pattern in turn, uses the moving

inversions algorithm with patterns of 32-bit wide (on 32-bit builds) or 64-bit

wide (on 64-bit builds) walking ones and walking zeros. Unlike previous tests,

the pattern is rotated 1 bit on each successive address.



### Test 7 : Block move, 64 moves



This test stresses memory by using block move (movs) instructions and is based

on Robert Redelmeier's burnBX test.



In each memory region in turn, memory is initialized with shifting patterns

that are inverted every 8 bytes. Then blocks of memory are moved around using

the movs instruction. After the moves are completed the data patterns are

checked. Because the data is checked only after the memory moves are completed

it is not possible to know where the error occurred. The addresses reported

are only for where the bad pattern was found. In consequence, errors from this

test are not used to calculate BadRAM patterns.



### Test 8 : Random number sequence



In each memory region in turn, each address is written with a random number,

then each address is checked for consistency and written with the complement

of the original data, then each address is again checked for consistency.



### Test 9 : Modulo 20, random pattern



In each memory region in turn, and for each pattern in turn, uses the

Modulo-20 algorithm with patterns of a random number and its complement.

The random number is different on each test pass so multiple passes increase

effectiveness.



### Test 10 : Bit fade test, 2 patterns



Across all memory regions, and for each pattern in turn, initialises each

memory location with a pattern, sleeps for a period of time, then checks

each memory location for consistency. The test is performed with patterns

of all zeros and all ones.



## Known Limitations and Bugs



Please see the list of [open issues](https://github.com/memtest86plus/memtest86plus/issues)

and [enhancement requests](https://github.com/memtest86plus/memtest86plus/discussions)

on GitHub.



Feel free to submit bug reports!



## Code Contributions



Code contributions are welcomed, either to fix bugs or to make enhancements.

See the README_DEVEL.md in the doc directory for some basic guidelines.



## Acknowledgments



Memtest86+ v6.0 was based on PCMemTest, developed by Martin Whitaker, which

was based on Memtest86+ v5.01, developed by Samuel Demeulemeester, which in

turn was based on Memtest86, developed by Chris Brady with the resources and

assistance listed below:



 * The initial versions of the source files bootsect.S, setup.S, head.S and

   build.c are from the Linux 1.2.1 kernel and have been heavily modified.



 * Doug Sisk provided code to support a console connected via a serial port.

   (not currently used)



 * Code to create BadRAM patterns was provided by Rick van Rein.



 * The block move test is based on Robert Redelmeier's burnBX test.



 * Screen buffer code was provided by Jani Averbach.

   (not used by Memtest86+ v6.0)



 * Eric Biederman provided all of the feature content for version 3.0

   plus many bugfixes and significant code cleanup.



 * Major enhancements to hardware detection and reporting in version 3.2, 3.3

   and 3.4 provided by Samuel Demeulemeester (from Memtest86+ v1.11, v1.60

   and v1.70).



In addition, several bug fixes for Memtest86+ were imported from

[anphsw/memtest86](https://github.com/anphsw/memtest86).