It is a question, when I use a bootable CD to run it. It looks never stop.
Finally I got the answer from the forum of Memtest86+.
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.
via FAQ
