Memtest86+ FAQ v1.21
By R.R. van der Vossen (Wichetael)
Latest update 2007-02-28


QUESTIONS
---------

General
- What is memtest86+, what do I use it for? [revised]
- My question isn't answered in this FAQ, what do I do? [revised]

Running memtest
- How do I get it to run? [revised]
- I want to use memtest on a multiboot CD, how do I do this? [revised]

Using memtest
- How long does memtest run? How do I stop it?
- Which memory is tested?
- Can I print an error report, or write it to a file? [revised]

About the errors reported
- How many errors are acceptable?
- What do I do when I get errors? [revised]
- I'm getting errors in test #x, what doest that mean?
- I'm getting errors in test #5 and/or #8 and have read a lot about it.
- I'm getting errors in memtest on one machine, but not when I put the same
memory in another, what does that mean?
- I'm getting errors with memtest, but not in some other memory test or
vice versa.
- If memtest86+ shows no errors does that mean my memory is not defective?
[revised]
- What is elimination of factors? [new]

Problems starting memtest
- When I run install.bat it doesn't write anything to floppy.
- When I boot memtest86+ all I get is a never ending string of numbers.
- When I boot memtest86+ all I get is a DOS prompt. [new]

Problems running memtest
- When I select BIOS-ALL I get many errors or my machine crashes.
- Memtest freezes or my system crashes/reboots.
- My chipset is not recognised or the timing info is not shown. [revised]
- I have more memory than memtest is reporting.
- Why are the speeds incorrectly reported?

Questioned mark with [new] or [revised] are new or revised since v1.11, this
does not include small fixes and semantical clarifications.

ANSWERS
-------

General
-------

- What is memtest86+, what do I use it for?

Memtest86+ is a utility designed to test whether your memory is in working
order. It repeatedly writes an enormous amount of different patterns to all
memory locations and reads them back again and verifies whether the result
of the read is the same as what was written to memory.

There can be a multitude of reasons for running memtest, but foremost of
all is of course to test whether your memory modules might be bad. Whenever
you suspect your modules to be bad because of system crashes, lockups or
reboots it would be nice to know whether the modules are in working order.
Memtest86+ is a utility which tries to answer that question for you.

Another common use exists in the overclocking scene. When overclocking a
system you are essentially pushing your system to the limits and at some
point it will simply give way and break. Unfortunately there isn't a clear
cut way of deciding whether a system is still working correctly. Because of
the complexity of a computer, a system which is pushed to the limits doesn't
just break completely when it starts to fail, instead little errors start
showing up in many different places in the system growing more frequent and
widespread the more the system is pushed. Each one of these little errors
can lead to a crash of your system but can also go unnoticed for days or
weeks in a running system. The art so to speak of overclocking is thus to
push the system as far as it can go without introducing any such errors. As
memory is usually one of the first places that such errors start coming up
a memory test is very useful.

Do note however that memtest86+ is NOT a diagnostic utility, memtest cannot
tell you what in your system is defective if anything. Memtest is a tool to
quickly asertain whether a particular system has a correctly functioning
memory subsystem. You need good old logic to determine the cause of any
errors reported by memtest through elimination of factors.

- My question isn't answered in this FAQ, what do I do?

Firstly check out the FAQ which is posted on the memtest86+ official forum
over at http://forum.memtest.org/. The latest version of the FAQ is always
posted there.

If you have any further questions about memtest, feel free to post them at
the memtest86+ official forum over at http://forum.memtest.org/. Bear in
mind though that this forum is only for questions or remarks regarding
memtest86+, i.e. reporting bugs, suggesting improvements for memtest,
posting cpu-z dumps of unrecognised chipsets and asking for help in using
memtest.

The forum is not for asking help on your fixing your computer problems, in
particular the memtest86+ forum is not a general tech support forum. Many
such fora exist on the internet however, so please take any such
questions/discussions to an appropriate forum. In particular, as is detailed
in this FAQ, we simply can not help you interpret the results of memtest.

Please do not post threads on the forum with questions already answered in
this FAQ or requests for help in solving a hardware issue or interpretation
of memtest results. Any such threads will be removed.

Remember, memtest can not tell you which component is defective or which
setting is incorrect. Memtest can tell you, however, whether your memory
subsystem is working correctly. Using memtest as a tool you will have to
locate the problem yourself through elimination of factors.

Running Memtest
---------------

- How do I get it to run?

There are several ways to use memtest, which are described below:

* Run from floppydisk

Memtest86+ is directly executable by any modern x86 compatible machine,
by writing the bootable binary to a floppy disk one can boot from the
disk to run memtest.

Simply download the appropriate package, the Pre-Compiled Bootable Binary
(.gz) package for Linux users and the Pre-Compiled package for Floppy
(DOS - Win) for Windows users.

For Windows, unzip the package into a directory like C:\memtest, insert a
blank floppy into your a: disk drive and run the install.bat file. As the
install prompts you, to use memtest directly, leave the disk in the drive
and reboot your machine.

For unix, unpack the package into your home directory, insert a blank
floppy into your floppy drive and execute 'dd if=~/memtest+-1.xx.bin
of=/dev/fd0 conv=osync' replacing 1.xx with the correct version number of
the memtest86+ you downloaded. To run memtest immediately reboot your
machine. If you run linux you need to specify 'conv=sync' instead of
'conv=osync' which is used on BSD unices.

Your machine should now boot from the disk, display the word Loading
folowed by a series of periods and then show a screen much like the
screenshots on the memtest86+ web page. The test is automatically
started.

If your machine simply boots back into Windows/Linux you will most likely
have to configure your BIOS to attempt to boot from floppy disk on
startup, refer to your computer's/mainboard's manual how to do this.

When you are done testing simply remove the floppy and reset your
computer, if ever you want to execure the test again simply reinsert the
disk and reboot/start your computer.

* Run from CD

Memtest86+ is directly executable by any modern x86 compatible machine,
by writing the iso to a CD one can boot from the CD to run memtest.

Simply download the appropriate package, the Download - Pre-Compiled
Bootable ISO (.gz) for Linux users and the Pre-Compiled Bootable ISO
(.zip) for Windows users.

For Windows, unzip the package into a directory like C:\memtest. You will
now see a file called memtest86+-1.xx.iso in this directory. You will
need to burn this file to a CD with a CD recording program. Do note
however that you should not make a regular data CD on which you for
instance write your text documents and holiday photographs. Instead the
iso file is a so called image of a CD, it is a direct copy of a CD. Your
CD recording program will most likely have a feature called burn image or
something to that effect which you should use to burn the CD. Do NOT under
any circumstances select to create a bootable CD. The memtest ISO image is
already bootable. You need NOT create a new CD, you need to burn a CD
image. Usually you can simply double click the iso file in the Windows
explorer which will start your CD burning application and prompt you to
burn the CD.

For unix, unzip the package into your home directory. and execute
'cdrecord dev=<your burner> ~/memtest86+-1.xx.iso' where you replace
<your burner> with the scsi address of your CD burner and replace 1.xx
with the correct version number of the memtest86+ you downloaded.

When the burning is completed your drive will most likely have ejected the
CD and you should have a bootable memtest86+ CD. To run the test directly
reinsert the CD and reboot your machine.

Your machine should now boot from the CD, display the word Loading
folowed by a series of periods and then show a screen much like the
screenshots on the memtest86+ web page. The test is automatically
started.

If your machine simply boots back into Windows/Linux you will most likely
have to configure your BIOS to attempt to boot from CD-ROM drive on
startup, refer to your computer's/mainboard's manual how to do this.

When you are done testing simply remove the CD and reset your computer,
if ever you want to execute the test again simply reinsert the CD and
reboot/start your computer.

* Run from USB Flash drive

FIXME

* Run from boot manager

In grub you can simply add an entry like the following;

title Memtest86+
kernel /boot/memtest86+.bin

You would of course need to copy the memtest86+-1.xx.bin file from the
distribution to /boot/memtest86+.bin.

Note that on some computers this does not work and results in an "Error
28: Selected item cannot fit into memory" reported by grub. The problem
here is that memtest86+ uses the legacy linux loading mechanism which
expects to be loaded at 0x9A000 in memory. On some systems the BIOS uses a
part of the memory closely after this address and correctly reserves it in
the e820 memory map. Grub will then fail to load memtes86+ over this
reserved memory area, which is the correct behaviour. For now there is no
way to circumvent this. The memtes86+ loader should be rewritten to use a
newer loading mechanism, but this will be quite a big task. It is unclear
when this will be realised.

- I want to use memtest on a multiboot CD, how do I do this?

This is of course very dependent on which boot loader you use for your CD.
Below is a description of how to set up a multiboot CD including memtest86+
with isolinux and Bootable CD Wizard, if you have experience with any other
bootloader(s) please consider writing a small description of using memtest
with that bootloader for the FAQ.

* Isolinux

For general instructions on how to make a bootable CD with isolinux see
the syslinux website and the manual. What you need to do to get memtest
working is as follows.

Download the Pre-Compiled Bootable Binary, the .gz if you are working
under unix, the .zip if you are working under Windows. Unpack the file
from the package and rename it to an 8.3 filename with an extension other
than .bin, renaming to 'memtest' (without an extension) is a good choice.

Put the file somewhere in your CD directory structure, for example in
images/memtest and edit your config file to include the following:

label memtest
kernel /images/memtest

If you want to boot memtest automatically insert or change a line at the
top to:

default memtest

If you want to display a prompt from which you can start memtest add or
change the lines at the top to: (Change the timeout to suit your needs)

prompt 1
timeout 200

* Bootable CD Wizard

For Windows, open the memtest binary with a hex editor and pad the file
with zeros to 360KB (368640 Bytes).

For linux you can execute the following command to accomplish the same,
replace 1.xx with the correct version number of the memtest you
downloaded.

dd if=memtest86+-1.xx.bin of=memtest.img bs=360k count=1 conv=sync

On a BSD system you would need to use 'conv=osync' instead.

You now have a 360KB floppy image which you can use with Bootable CD
Wizard, please see the appropriate documentation on how to boot the
floppy image with Bootable CD Wizard.

Using Memtest
-------------

- How long does memtest run? How do I stop it?

Memtest runs indefinately unless you stop it. It does however repeat the
same tests over and over again. Memtest86+ contains a number of different
tests which each take different approaches in trying to expose any errors
in your memory. In the top right of your screen you can see the progress of
each test in the lower of the two progress bars. The topmost progress bar
shows the progress of a pass, each pass consists of all the tests in the
memtest suite.

Thus all tests are executed in one pass, so does that mean that no errors
will show after the first pass if that pass didn't reveal any errors? Well
no, there are several reasons why errors might only show up after a number
of passes. Firstly as of this writing, the latest version of memtest also
includes a test which uses random test patterns, each pass these patterns
will of course be different. Secondly some types of errors simply don't show
up until the system has been running for a while or are very critical on a
certain timing condition, are thermal in nature, or other such conditions.

To conclude, one successful pass of memtest will give you a pretty good
idea that your memory is ok, only in rare cases will there be errors
showing after the first pass. To be sure though simply have the test run
overnight or even for a couple of days depending on the level of importance
of the system.

- Which memory is tested?

As much as possible of the system memory is tested. Unfortunately memtest86+
can usually not test all of the memory. The reason for this is that todays
processors and BIOSes have become so complex that they require a small
amount of memory to keep accounting data of the processor and BIOS state
respectively. If memtest were to write over these areas the state of the
processor or BIOS becomes invalid and it's behaviour unpredictable. Alas it
is also impossible to relocate these areas in the memory.

This means that a small area of your memory can not be tested by memtest.
If this part of the memory is defective you will know soon enough though as
the processor, parts of the processor or the BIOS simply won't work
correctly if this part of your memory is defective. Do realise though that
in very rare cases memtest will show no errors even though the module is
defective, not because memtest can't detect the error, but because memtest
can't test the area the error is located in.

- Can I print an error report, or write it to a file?

No, printing an error report is not possible, nor is it possible to write
such a report to a file on disk. The reason for this is that it is far from
trivial to implement such a feature. Printing a report presents a big
problem, as nowadays just about any printer is USB driven. Adding support
for this would require a very large addition to the memtest code. Writing a
report to the floppy disk represents an equally large problem. The memtest
floppy is not a DOS floppy, so it would require a major addition to the
source base in order to support this. Any major addition to the code is a
bad idea as it introduces new possibilities for bugs in the code, so for any
such addition the advantages have to outweigh this major disadvantage. In
the case of this feature this is certainly not the case.

Though besides all this there is a much better reason that this feature is
not available, which is the simple fact that any such report is completely
useless, it proves or disproves nothing. Firstly any such report could of
course be faked, but far more importantly memtest can not tell you which
part, if any is defective. It can only tell you whether your memory
subsystem is working as it should or not. Memtest is not a diagnostic
utility, it cannot tell you what is wrong with your computer. Memtest is a
tool to be used in troubleshooting techniques such as elimination of factors
to quickly, reproducibly and dependably expose problems in the memory
subsystem.

About The Errors Reported
-------------------------

- How many errors are acceptable?

No errors are acceptable. Even if there is just one error, something is
amiss which can cause your system to crash. Of course what the cause of the
errors is you will still have to determine.

- What do I do when I get errors?

Firstly, don't start drawing any conclusions. You only know that memtest86+
is giving you errors, not what the cause is. Unfortunately it is not a
straightforward exercise to decisively test the memory modules themselves in
an actual system. This is because a computer is not just built up of some
memory, but also includes many other elements such as a memory controller,
cache, a cache controller, algorithmic and logic units, etc., etc., all of
which contribute to the machine. If there are faults in any of these other
parts of the computer you will likely also see errors showing up in memtest.

So what to do? You need to find the actual cause of the problem. The best
known troubleshooting technique for this is elimination of factors, which is
a method of incrementally eliminating factors from the set of all possible
causes of the problem. See the question 'What is elimination of factors' for
more information on this.

First verify that the BIOS settings of your machine are correctly
configured. Look up the memory timing settings applicable to the brand and
type of memory modules you have and check they match your BIOS settings,
correct them if they don't and run memtest again

Ok, you have all the settings correctly set and you're still getting errors.
Next thing to do is remove as many factors as we can, this means
disconnecting/removing anything that is not essential to run the test, i.e.
disconnect or remove all external devices, as many IDE/SCSI/S-ATA/Floppy
devices and add-in cards as you can. If the problem still persists then of
course a very likely cause are the memory modules, the logical course of
action is to look into them further.

If you are well stocked, have a few other machines at your disposal, or
just want to spend the cash for some new modules the best way to test if
the cause is in your memory modules is just to replace them and test again.
If you are less fortunate and do not have such modules at your disposal the
only viable way to get the system further diagnosed is to bring it in to a
computer repair shop, though there is still something you can do.

If you have more then one module in your system, test them one by one, if
one is consistently giving errors and another is consistently showing no
errors it's a pretty good bet that the module giving the errors is simply
defective. To exclude the possibility that a defective slot is throwing
your results, use the same slot to test each different module.

If each module by itself shows no errors, but when you place two or more
modules into the machine at the same time you do get errors, you are most
likely stuck with a compatibility issue and unfortunately there isn't a
whole lot you can do about it. Be sure to check your computer/motherboard
manual to see if the setup you are trying is allowed, some boards require
special restrictions in the sizes of modules, the order of modules, the
placement of double sided and single sides modules and more of such things.

In some cases having more than one memory module in the system also affects
the timing of the memory system, which might just be enough for the system
to start giving error. The question is whether this is just an unfortunate
combination of factors or whether there is actually a defective component in
the system. And in the latter case which component is the problem.
Elimination of factors is the way to diagnose this. If all components are
actually in order you may simply need to relax the memory latencies a little
bit to relieve the problem.

If you have only one module in your system, or all modules are giving
errors, there are only very few options left. The only thing you can do
really is to try the module(s) in another slot. Finally simply try out
different orders of the memory modules, although your manual might not
mention anything on the matter sometimes there simply exist timing or other
issues which can be resolved by changing the order of your modules. And of
course test each slot by putting a single module into that slot and running
memtest on it.

In the end if you still have not been able to localize the problem you will
have to find a replacement module to establish whether the problem lies in
your modules. See if you can borrow a module from someone else.

When you have replaced the memory by new memory and the errors still
persist, first check if you can rule out any compatibility issues or timing
issues. If you are sure the memory should work in the system the cause of
the errors must obviously lie someplace else in the system.

The only way to find out where, is by method of elimination of factors.
Simply start replacing and/or removing parts of your computer one by one,
running memtest each time you changed anything, until the errors are
resolved. See the question 'What is elimination of factors?' for a more
detailed explanation of this.

- I'm getting errors in test #x, what doest that mean?

Interpreting memtest results is as scientific an endeavour as testing
whether a person is a witch by the methods used in Monty Python's Holy
Grail. In short, don't even start, it's not going to get you anywhere. Just
interpret any error as you should any other and use the methods descibed in
the previous question to determine the cause.

- I'm getting errors in test #5 and/or #8 and have read a lot about it.

Yes, there are just about enough discussions on the topic to fill a book,
but it all boils down to the answer given above. The only thing that can be
said is that many a time, when memory latencies are incorrectly set in the
BIOS you will likely experience errors in test #5 and in versions prior to
v1.40 also in test #8. This does however NOT mean that errors in these tests
are always the cause of incorrect settings, your memory or some other
component might just as well be defective.

- I'm getting errors in memtest on one machine, but not when I put the same
memory in another, what does that mean?

It can mean one of two things:

* The machine that is giving the errors is defective. Errors don't just
orginate from the memory module itself, but can also be caused by
defects in the cpu, chipset, motherboard, PSU and even by timing issues
introduced by any other component in the machine.

* The machine giving the errors is imposing stricter timing than the other
which the memory module simply can't cope with. If the module should
work with the machine according to its specifications then it most
likely is defective.

- I'm getting errors with memtest, but not in some other memory test or vice
versa.

Different memory tests test the memory in different ways, it could easily
be that an error not picked up by one test, is picked up by another. Keep
in mind though that a test such as memtest86+ can only prove things that
are there, it can not prove that there are no errors in the memory. A full
pass of memtest86+ gives you a very good indication that the memory is ok,
but it is never a definitive proof of correctly functioning memory.

Thousands of people use memtest86+ daily and as far as we know there are no
known issues with memtest86+ giving false errors. If any such bug were to
occur in a future release of memtest86+, believe me, we will quickly know
about it and the error will be corrected. In general you can assume that
the problem is not in memtest86+ but that the problem is caused by
something else, so unless you have some very exotic hardware please do some
tests yourself by swapping out components, search google, update to the
latest BIOS version, experiment with memory timings, etc. before you ask
questions about it on the forum.

- If memtest86+ shows no errors does that mean my memory is not defective?

Of course no answers are definitive, no matter how good memtest86+ is or
will become there is always the possibility that a particular type of error
will go unnoticed. As long as you are having no problems with the system it
will be pretty safe to say that the modules are good. If you are having
problems with the system however you will just have to check elimination of
factors, ie swapping the modules for new ones and/or testing with modules of
a different brand/type. See the question 'What is elimination of factors?'
for more information on this method.

- What is elimination of factors? [new]

Elimination of factors is a well known and tried and true method of
troubleshooting. The idea is that you have a reproducible error, such as
errors reported by memtest86+, but it could also be a crash when running a
certain program, artifacts in the video output of the computer, incorrect
results of mathematical calculations, etc. etc.

The idea of the method is to change a factor in the entire system and rerun
the test after each change. If the test still produces the error then the
problem is not in the factor just changed, if it doesn't produce the error
anymore the problem is most likely in the factor just changed. More testing
needs to follow though.

Factors to change are numerous, e.g. you can replace a part of the system
with a part of the same brand and model. Note that replacing a part with a
part of a different brand and model you are actually changing more than one
factor at a time, this is important in determining the actual cause of the
problem. Other factors to change are system settings, in the context of this
FAQ this mostly concerns BIOS settings. Yet other factors are software
(including the BIOS or other firmware) versions, and in some cases
reinstallations of said software.

Ideally you have the least number of factors to contend with, so the first
thing to eliminate is usally as much software as possible as this is the
least standardised and the least predictable. This is also the reason why
memtest86+ is written not to use an OS of any kind, instead it boots the
system itself and runs outside of any operating system.

Next you remove as much parts from the computer as you can that are not
essential for the computer to run or the test to be performed, for example
you can disconnect all external hardware, all harddrives, all optical
drives, the floppy drive and card reader, you can remove any add-on cards
except for the graphics card, etc. Of course you need to leave the device
that you load memtest from connected to the system.

Assuming the system is still producing the same error, it is time for
looking at the BIOS settings try disabling any non-critical features and
toggling many of the options, while of course keeping the specs of your
system in regard. Next you turn to restting the BIOS after which you upgrade
or reflash the BIOS. Note that you might erase DMI information containing
your Windows license from the BIOS by flashing it. If you purchached your
computer from an OEM supplier with a Windows recovery you more than likely
do not want to flash the BIOS.

Next you want to replace parts of the core system, i.e. the memory modules,
the processor(s), the videocard, the psu, the motherboard etc. Preferably
these parts should be replaced by parts of the same brand and model. If you
do not have such parts available to you the only viable option is to consult
a computer repair shop or the technical department of your computer
supplier.

If the error is still not resolved when all parts have been replaced there
might be several things going on. The first thing to check is of course if
the parts you used to swap the original parts with are in fact not
defective. Replace them again, preferably from a different batch of the same
brand and model. The next thing to check is if there exists a compatibility
problem between any two of the parts. The computer world is governed by
standards, but every manufacturer always seems to have their own idea on how
to interpret these standards. This means that although most parts work okay
together with most other parts, there are some parts that simply do not work
correctly with particular other parts. Replace the parts with parts of a
different brand and model to see if the problems are resolved.

When the problem does appear to be resolved by changing a factor, it is
pretty likely that the cause is in that factor, but this cannot be
guaranteed. For example when removing or replacing an internal component the
BIOS usually takes note of this en runs a special part of it's program to do
any necessary administrative work. In some cases this on itself can resolve
problems, or temporarily relieve them. It is therefore always import that,
when you find the change that resolves the problem, you reverse this change
and see if the problem comes back. If the problem does come back then you
can be reasonably certain that the actual cause of the problem is within the
factor changed. If however the problem does NOT come back you are
essentially back to square one. This is one of the most difficult situations
to properly diagnose, and in fact you cannot really be sure to resolve such
a problem with the elimination of factors technique. There are however not
any viable other options to diagnose such a problem without deeper access to
the system or special diagnostic equipment.

Problems Starting Memtest
-------------------------

- When I run install.bat it doesn't write anything to floppy.

You most likely have unpacked the memtest+-1.xx.floppy.zip file into a
folder with a long pathname and/or containing + and - signs. It seems
rawrite doesn't like that. Just move the files you unpacked to a directory
like c:\memtest and execute it from there.

- When I boot memtest86+ all I get is an endless string of numbers.

When booting memtest from a floppy disk you can sometimes see a message
much like the following scrolling up endlessly on the screen:

X:8000
AX:0212
BX:8600
CX:0201
DX:0000

This is the BIOS reporting floppy disk read errors. Try re-writing the
disk. If that does not work replace the disk.

- When I boot memtest86+ all I get is a DOS prompt.

You did not install memtest86+ correctly to floppy or CD. Memtest86+ does
not use DOS to boot, in fact it does not have anything whatsoever to do with
DOS nor any other operating system. Memtest runs outside of the operating
system and boots on its own. If you get a message stating that DOS is
loading, or you get a DOS prompt, reinstall memtest to floppy or CD and be
sure to follow the directions in this FAQ precisely. Again you must not
create a bootable floppy disk or CD, memtest is already bootable itself.

Problems Running Memtest
------------------------

- When I select BIOS-ALL I get many errors or my machine crashes.

This is normal. With todays computers this option should never be selected.
When selecting BIOS-ALL memtest will ignore the e820 memory map supplied by
the BIOS and will also test areas reserved by the BIOS for the processor or
the BIOS. See the question about which memory is test for more information
on this.

- Memtest freezes or my system crashes/reboots.

Check that you have USB legacy support disabled in your BIOS setup. Some
BIOSes have a bug in them that reports the reserved memory areas
incorrectly in the e820 memory map. This causes memtest to write over the
memory area used by the USB legacy support resulting in freezes or reboots.

Any crashes or reboots can also be caused by a myriad of other problems,
including incorrent settings and defective parts. On the whole you can
pretty much assume that the cause of memtest crashing is with your machine
and not with memtest. Thousands of people use memtest on a daily basis and
should experience the same problems if the cause is with memtest.

When you do think you've found a bug in memtest first try to confirm
(replicate) the bug on another system, preferably by someone else. Also
make sure the problem is not caused by any of the BIOS settings, any BIOS
bugs or the media you have memtest written on. When you're sure you've
found a bug in memtest please report it on the memtest forum.

- My chipset is not recognised or the timing info is not shown.

Most of the current chipsets are already supported by memtest86+ and many of
the newly released chipsets will be added to memtest86+, sometimes even
before their release. There are however still some chipsets which are not
recognised by memtest86+, this is not a problem for the tests themselves.
Memtest86+ does not need to know the chipset to perform the testing, nor
does it perform better or more accurate tests if it does know the chipset.
In fact the test performed are exactly the same for recognised and
unrecognised chipsets. The chipset make and type are purely of informational
value to the user.

The same holds for the timing information displayed by memtest86+. This
information is only displayed for the more popular chipsets such as the
i915 for example. For VIA chipsets this information is deliberately left
out because of their buggy and inconsistent nature.

If you encounter a chipset which is not recognised by memtest86+ and is not
from somewhere back in the stoneage, please post a cpu-z dump on the memtest
forum. There is a special sticky thread to post cpu-z dumps. Most likely the
chipset will then be added in the next release of memtest86+.

- I have more memory than memtest is reporting.

Memtest retrieves a memory map from the BIOS. This map informs memtest
where the memory is located and what parts of the memory are reserved.
Sometimes the ammount of memory on the map is less than the total amount of
installed memory, this is usually but not necessarily due to video frame
buffers, a part of the system memory which is used by the on-board graphics
card. This is basically not a problem other than that memtest86+ can not
test this reserved/hidden memory. In case of a video frame buffer you can
usually specify the size of the buffer in the BIOS, it would be wise to set
this to the lowest value while you are testing your RAM so that you can
test as much as possible.

Another cause of memory not appearing on the memory map can be that the
motherboard can simply not provide more than a certain amount of memory,
this can happen when there is more than 3GB of memory in the system. The
standard IA32 specification only has a 4GB addressing space, the top 1GB of
which is reserved for extension busses such as PCI, AGP and PCI-Express.

Besides memory not reported on the memory map there can also be memory
reserved by the BIOS, for the most part these are memory areas the BIOS
needs to provide certain functionalities, such as on-board devices. Again,
this is not really a problem for memtest, other than that memtest can not
test these areas. In order to reduce the reserved memory you can try to
disable as much features as you safely can in the BIOS. In some cases the
video frame buffer is represented as reserved memory instead of left out on
the memory map.

- Why are the speeds incorrectly reported?

It is not uncommon for a system to run slightly slower or slightly faster
than the settings made in the BIOS. If the speeds deviate by a couple of
MHz you should not worry about it. If it deviates by a significant margin,
eg it reads 333 instead of 400, then first of course check your BIOS
settings and make sure it's set to the correct speed. If you are sure that
the memory is running at the correct speed, but memtest is reporting a
completely different speed, please report so in the memtest forum, if at all
possible include a cpu-z report of the system in your post.


HISTORY
-------

v1.21 2007-02-28
- added a note saying to check the faq posted on the forum if the question
is not asnwered in the faq.

v1.20 2007-01-29
- fixed some typos
- revised many answers in order to clarify them
- added questions on DOS prompt and elimination of factors

v1.11 2006-05-15
- fixed some typos
- added some clarifications

v1.10 2006-03-26
- revised the layout
- reordered the questions
- added and revised questions

v1.00 2005-01-13
- initial release


LINKS
-----

- Memtest86+ Homepage
http://www.memtest.org/

- Memtest86+ Official Forum
http://forum.memtest.org/

- Memtest86 Homepage (Memtest86+ is based upon this)
http://www.memtest86.com/