- 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 these such errors start coming up  a memory test is very useful.- 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 Linux, unpack the package into your home directory, insert a blank    floppy into your floppy drive and execute 'dd if=~/memtest+-1.xx.bin.gz    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.    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.    For linux, 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+ your downloaded.    When the burning 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 execure the test again simply reinsert the CD and    reboot/start your computer.  + Run from USB Flash drive    FIXME  + Run from boot manager    FIXME- How long does memtest86+ run? How do I stop it?  Memtest86+ 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, 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.  - 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 your errors, not what the cause is. Unfortunately it is not a  straightforward exercise to decisively test the memory 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, 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? 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