how long would memtest86 take to run in these cases. and would it ever go on indefinitely?

Solution 1:

Would it go on indefinitely? Just continuously doing more and more passes?

I believe so.

Is it common for people to just do one pass

It's common to run it for multiple passes, recommended is to run it for atleast 8 hours. It's not uncommon to see it run for 12+ hours

btw, what is the difference between memtest86 and memtest86+?

memtest86+ is a port of memtest86, supports more recent processors,chipsets and higher capacity RAM.