MemTest86 Technical Information


What's New in MemTest86 for the UEFI platform (Version 5 and later)?

MemTest86 supports booting from both the newer UEFI platform and the traditional BIOS. When booting from UEFI, MemTest86 has access to additional services not available in BIOS including:

  • Native 64-bit support
  • No longer requires the use of the PAE workaround to access more than 4GB of memory. (PAE = Physical Address Extension)
  • Mouse support, where supported by the underlying UEFI system. On older systems a keyboard is still required.
  • Improved USB keyboard support. The keyboard now works on systems that fail to emulate IO Port 64/60 correctly. So Mac USB keyboards are now supported.
  • Improved multi-threading support, where supported by the underlying UEFI system.
  • Reporting of detailed RAM SPD information. Timings, clock speeds, vendor names and much more.
  • Support to writing to the USB drive that MemTest86 is running from for logging and report generation. In all prior MemTest86 releases, there was no disk support.
  • Use of GPT. (GUID Partition Table)
  • ECC RAM support (limited hardware support, ongoing development)
    • Detection of ECC support in both the RAM and memory controller
    • Polling for ECC errors
    • Injection of ECC errors for test purposes. (limited hardware only)
  • Support for DDR4 RAM (and associated hardware), including retrieval and reporting of DDR4-specific SPD details. This includes DDR4 RAM that support Intel XMP 2.0 DDR4 RAM timings
  • Option to disable CPU caching for all tests
  • Having a configuration file to allow settings to be pre-defined without the need for keyboard input. This can help with automation.
  • Support for Secure Boot.
  • Speed improvements of between 10% and 30%+. Especially for tests, #5, #8 & #9. This is the result more moving to native 64bit code, removing the PAE paging hack, switching compilers and using faster random number generation algorithms.
  • Addition of 2 new memory tests to take advantage of 64bit data and SIMD instructions.
  • See the What's New page for a complete list of changes.

See the feature comparison page for a summary of the differences between the various editions of MemTest86.

If UEFI is not supported on the system, the older v4 BIOS version is booted. MemTest86 can boot from a CD, USB flash drive or, with Linux systems, by the boot loader (for example, LILO or Grub). Any Windows, Linux or Mac system may be used to create the CD or USB flash drive. Once a MemTest86 boot disk has been created, it may be used on any x86 (PC/Mac) computer.

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Creating a MemTest86 boot disk in Windows

To create a MemTest86 bootable USB, CD or floppy in Windows, it is recommended that you download one of the Windows MemTest86 images.

Note: There is no difference in the resulting MemTest86 boot disk created using either the Windows or Linux/Mac images; the difference is merely that the images are packaged in a way that it is more suited for the respective operating system (eg. zip vs tarball).

Create a bootable CD-ROM:

  1. Download the Windows MemTest86 ISO image.
  2. Right click on the downloaded file and select the "Extract to Here” option. This places the CD-ROM ISO image into the current folder.
  3. Use the CD burning software available on your system to create a CD-ROM using the extracted ISO image. Be sure that you create a CD image from the ISO file rather than placing a copy of the ISO file onto a data CD. Look for “Burn Image from File” or similar option under the File menu of your CD burning software.

Create a bootable USB Flash drive:

  1. Download the Windows MemTest86 USB image.
  2. Right click on the downloaded file and select the "Extract to Here” option. This places the USB image and imaging tool into the current folder.
  3. Run the included imageUSB tool, it should already have the image file selected and you just need to choose which connected USB drive to turn into a bootable drive. Note that this will erase all data on the drive.

Create a bootable floppy (v4 only):

  1. Download the Windows MemTest86 floppy disk image.
  2. Right click on the downloaded file and select the "Extract to Here” option. This places the floppy disk image into the current folder.
  3. Creating a bootable floppy disk requires use of a third party program to write the floppy disk image to a disk. A number of programs are available to write the disk image. Rawwrite is a recommended free program available at: http://www.chrysocome.net/rawwrite. A more robust solution is WinImage, available at http://www.winimage.com/download.htm.
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Creating a MemTest86 boot disk in Linux/Mac

To create a MemTest86 bootable USB, CD or floppy in Linux/Mac, it is recommended that you download one of the Linux/Mac pre-compiled MemTest86 images. Advanced users may wish to build from source and optionally make source code changes.

Note: There is no difference in the resulting MemTest86 boot disk created using either the Windows or Linux/Mac images; the difference is merely that the images are packaged in a way that it is more suited for the respective operating system (eg. zip vs tarball).

Create a bootable CD-ROM:

  1. Download the Linux/Mac MemTest86 ISO image.
  2. UN-tar the package (tar xvzf MemTest86-*-iso.tar.gz). An ISO image file and a README file will be created in the current directory.
  3. Use the CD burning software available on your system to create a CD-ROM using the uncompressed ISO image. Be sure that you create a CD image from the ISO file rather than placing a copy of the ISO file onto a data CD. Look for “Burn Image from File” or similar option under the File menu of your CD burning software. On a Mac, you can use 'Disk Utility'. See this forum post for details.

Create a bootable USB Flash drive:

  1. Download the Linux/Mac MemTest86 USB image.
  2. UN-tar the package (tar xvzf MemTest86-*-usb.tar.gz). An image file and a README file will be created in the current directory.
  3. Follow instructions in the README to write the USB flash disk.

Create a bootable floppy (v4 only):

  1. Download the Linux floppy disk image.
  2. UN-tar the package (tar xvzf MemTest86-*-floppy.tar.gz). An image file and a README file will be created in the current directory.
  3. Follow instructions in the README to write the floppy disk.
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Usage

Booting MemTest86

MemTest86 supports booting from both UEFI and BIOS systems. Most newer systems are able to run the UEFI version of MemTest86, but all systems should be able to boot the traditional BIOS version.

To start MemTest86 insert the CD-ROM or USB flash drive into the appropriate drive and restart your computer. Note: If running on a UEFI system, the UEFI BIOS must be configured to boot from the device that MemTest86 is installed on. Most systems have an optional boot menu that is enabled be pressing a key at startup (often ESC, F9, F11 or F12) similar to the following:

UEFI BIOS Boot Menu

If available use the boot menu to select the correct drive. You may see both the UEFI and BIOS as separate options. Please consult your motherboard documentation for details.

On a Mac, you need to hold down the 'c' key while the computer is booting to boot from CD. To boot from USB, you need to hold down the ALT / Option key on the Mac keyboard while powering on the machine.

Using a Serial Console

For systems without video support, MemTest86 can run in serial console mode from both UEFI and BIOS systems. For MemTest86 v4, select option 5 from the menu to enable output to serial console. You will not need to do anything for MemTest86 v5 or later as it will automatically use the serial console, provided that the UEFI BIOS has been configured to redirect the console to the serial port. No GUI support is available when using the serial console so all test configurations must be done using the configuration file.

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Configuring MemTest86

When MemTest86 boots, a splashscreen is displayed with a 10 second countdown timer which when expires, automatically starts the memory tests with default settings. Pressing a key or moving the mouse shall stop the timer. To configure the memory tests, select 'Config' and the main menu is displayed. The main menu allows the user to customize the memory test settings such as the specific tests to execute, address range to test and which CPU(s) are used in testing.

MemTest86 Main Menu

The Main Menu is structured as follows:

  • System Info - displays the hardware details of the system
  • Test Selection - specifies which tests to enable, and how many passes to run
  • Address Range - specifies the lower and upper address memory limits to test
  • CPU Selection - select between Single, Parallel, Round Robin and Sequential modes
  • Start - start executing the memory tests
  • RAM Benchmark - performs benchmarking tests on RAM, and graphs the results on a chart
  • Settings - configure general MemTest86 settings such as language selection
  • Exit - exits MemTest86 and reboots the system

(Pro version only) Memory test parameters can also be set via a configuration file (mt86.cfg) that is loaded on startup, without the need to manually configure the memory tests every time MemTest86 is run. This is useful especially in testing environments where memory tests need to be executed in an automated fashion without user intervention. The mt86.cfg config file need to be placed into the EFI\BOOT folder on the USB drive. The following is an example of a MemTest86 configuration file:

TSTLIST=0,1,3,5,8
NUMPASS=3
ADDRLIMLO=0x10000000
ADDRLIMHI=0x20000000
CPUSEL=PARALLEL
CPUNUM=1
ECCPOLL=0
ECCINJECT=0
MEMCACHE=0
PASS1FULL=0
ADDR2CHBITS=12,9,7
LANG=ja-JP
REPORTNUMERRS=10
             
Parameter Description
TSTLIST List of tests to execute in the test sequence. Each test is specified by a test number, separated by a comma.
NUMPASS Number of iterations of the test sequence to execute. This must be a number greater than 0.
ADDRLIMLO The lower limit of the address range to test. To specify a hex address, the address must begin with '0x'. Otherwise, the address shall be interpreted as a decimal address.
ADDRLIMHI The upper limit of the address range to test. To specify a hex address, the address must begin with '0x'. Otherwise, the address shall be interpreted as a decimal address.
CPUSEL One of the following CPU selection modes:
{ 'SINGLE', 'PARALLEL', 'RROBIN', 'SEQ' }
CPUNUM The CPU # of the specific CPU to test. This parameter only has an effect if CPUSEL is set to 'SINGLE'.
ECCPOLL Specifies whether ECC errors shall be polled.
0 – Polling disabled, 1 – Polling enabled
ECCINJECT Specifies whether ECC error injection shall be enabled.
0 – ECC injection disabled, 1 – ECC injection enabled
MEMCACHE Specifies whether memory caching shall be enabled/disabled during testing.
0 – Memory caching disabled, 1 – Memory caching enabled
PASS1FULL Specifies whether the first pass shall run the full or reduced test. By default, the first pass shall run a reduced test (ie. fewer iterations) in order to detect the most obvious errors as soon as possible.
0 – Reduced test, 1 – Full test
ADDR2CHBITS List of bit positions of a memory address to exclusive-or (XOR) to determine which memory channel (0 or 1) is used. This is useful if you know that the memory controller maps a particular address to a channel using this decoding scheme. If this parameter is specified and MemTest86 detects a memory error, the channel number will be calculated and displayed along with the faulting address. Each bit position specified is separated by a comma. For example,
ADDR2CHBITS=1,8,9
will XOR bits 1,8,9 of the address to determine the channel.
LANG Specifies one of the following languages to use:
{
    'en-US',  // English
    'fr-FR',  // French
    'es-AR',  // Spanish (Latin American)
    'de-DE',  // German
    'ja-JP',  // Japanese
    'zh-CN',  // Chinese (Simplified)
    'zh-HK'   // Chinese (Traditional)
}
REPORTNUMERRS Number of the most recent errors to display in the report file. This number must be no more than 5000.
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Test Results

At the end of the test, a summary of the test results is displayed, as shown in the following screenshot:

MemTest86 Test Summary

  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 mask of all bits that have been in error (hexadecimal).
  Bits in Error:
     Total bit in error for all error instances and the min, max and average
     bit in error of each individual occurrence.
  Max Contiguous Errors:
     The maximum of contiguous addresses with errors.
  ECC Correctable Errors:
     The number of errors that have been corrected by ECC hardware.
  Test  Errors:
     On the right hand side of the screen the number of errors for each test
     are displayed.

The user may also save the results as an HTML test report to a file. The test report appearance is fully customizable in the pro version. Here is an example of an HTML test report

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Troubleshooting Memory Errors

Please see the Troubleshooting Memory Errors page on what to do when MemTest86 detects an errory with memory.

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Execution Time

The time required for a complete pass of MemTest86 will vary greatly depending on CPU speed, memory speed and memory size. The pass counter increments after 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.

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Detailed Descriptions

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.

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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 test works as follows:

  1. Fill memory with a pattern
  2. Starting at the lowest address
    • check that the pattern has not changed
    • write the patterns complement
    • increment the address
    • repeat
  3. Starting at the highest address
    • check that the pattern has not changed
    • write the patterns complement
    • decrement the address
    • repeat

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 insure 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 less effective. It is possible to turn off cache but the memory buffering in new high performance chips can not be disabled. To address this limitation a new algorithm I call Modulo-X was created. This algorithm is not affected by cache or buffering. The algorithm works as follows:

  1. For starting offsets of 0 - 20 do
    • write every 20th location with a pattern
    • write all other locations with the patterns complement
    • repeat above one or more times
    • 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 (1a, 1b) and the read pass (1c) 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.

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Individual Test Descriptions

MemTest86 executes a series of numbered test sections to check for errors. These test sections consist of a combination of test algorithm, data pattern and cache setting. The execution order for these tests were arranged so that errors will be detected as rapidly as possible. A description of each of the test sections follows:

Test 0 [Address test, walking ones, no cache]

Tests all address bits in all memory banks by using a walking ones address pattern.

Test 1 [Address test, own address, Sequential]

Each address is written with its own address and then is checked for consistency. In theory previous tests should have caught any memory addressing problems. This test should catch any addressing errors that somehow were not previously detected. This test is done sequentially with each available CPU.

Test 2 [Address test, own address, Parallel]

Same as test 1 but the testing is done in parallel using all CPUs and using overlapping addresses.

Test 3 [Moving inversions, ones&zeros, Parallel]

This test uses the moving inversions algorithm with patterns of all ones and zeros. Cache is enabled even though it interferes to some degree with the test algorithm. With cache enabled this test does not take long and should quickly find all "hard" errors and some more subtle errors. This is done in parallel using all CPUs.

Test 4 [Moving inversions, 8 bit pattern]

This is the same as test 3 but uses a 8 bit wide pattern of "walking" ones and zeros. This test will better detect subtle errors in "wide" memory chips.

Test 5 [Moving inversions, random pattern]

Test 5 uses the same algorithm as test 4 but the data pattern is a random number and it's complement. This test is particularly effective in finding difficult to detect data sensitive errors. The random number sequence is different with each pass so multiple passes increase effectiveness.

Test 6 [Block move, 64 moves]

This test stresses memory by using block move (movsl) instructions and is based on Robert Redelmeier's burnBX test. Memory is initialized with shifting patterns that are inverted every 8 bytes. Then 4mb blocks of memory are moved around using the movsl 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. Since the moves are constrained to a 8mb segment of memory the failing address will always be less than 8mb away from the reported address. Errors from this test are not used to calculate BadRAM patterns.

Test 7 [Moving inversions, 32 bit pattern]

This is a variation of the moving inversions algorithm that shifts the data pattern left one bit for each successive address. The starting bit position is shifted left for each pass. To use all possible data patterns 32 passes are required. This test is quite effective at detecting data sensitive errors but the execution time is long.

Test 8 [Random number sequence]

This test writes a series of random numbers into memory. By resetting the seed for the random number the same sequence of number can be created for a reference. The initial pattern is checked and then complemented and checked again on the next pass. However, unlike the moving inversions test writing and checking can only be done in the forward direction.

Test 9 [Modulo 20, Random pattern]

Using the Modulo-X algorithm should uncover errors that are not detected by moving inversions due to cache and buffering interference with the algorithm.

Test 10 [Bit fade test, 2 patterns]

The bit fade test initializes all of memory with a pattern and then sleeps for a few minutes. Then memory is examined to see if any memory bits have changed. All ones and all zero patterns are used.

Test 11 [Random number sequence, 64-bit]

This test is the same as Test 8, but native 64-bit instructions are used.

Test 12 [Random number sequence, 128-bit]

This test is the same as Test 8, but native SIMD (128-bit) instructions are used.

Test 13 [Hammer Test]

The row hammer test exposes a fundamental defect with RAM modules 2010 or later. This defect can lead to disturbance errors when repeatedly accessing addresses in the same memory bank but different rows in a short period of time. The repeated opening/closing of rows causes charge leakage in adjacent rows, potentially causing bits to flip. This test 'hammers' rows by alternatively reading two addresses in a repeated fashion, then verifying the contents of other addresses for disturbance errors. For more details on DRAM disturbance errors, see Flipping Bits in Memory Without Accessing Them: An Experimental Study of DRAM Disturbance Errors by Yoongu Kim et al.
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Recover disk space on a flash drive

We have had a few users wondering how to get back the space on a USB drive once they have finished using MemTest86. The problem stems from the fact that the Windows Disk Management function doesn't allow for wiping or re-partitioning of USB flash drives. You can find the steps needed to reformat a USB flash drive to full capacity here.

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Help improve MemTest86

We are always looking for ways to improve MemTest86 for our users. Please send any general suggestions to Click to send mail (JavaScript required)

Translating MemTest86 to your language

Since MemTest86 v6, we have added support for allowing the user to select the language to use in MemTest86. Currently, the following languages are supported:

  • English
  • German
  • Spanish
  • French
  • Japanese
  • Chinese (Simplified)
  • Chinese (Traditional)

If your language is not available for selection, or would like to generously provide translations for the benefit of other users, you may download the following string file that contains all the strings in the program in English.

MemTest86 localization string file

Please follow the instructions in the file on how to provide translations for the text. Any translated text we receive may be included in the next version of MemTest86, with appropriate credit given.

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