20060327, 20:22  #1 
11·857 Posts 
prime95, torture test, and stability
Question: Imagine a computer has a hardware defect that is exposable through prime95's torture test. Is the probability of the torture test exposing this defect by failing a test the same in a 20hour run as it is in two 10hour runs?
I guess what I'm asking is whether the tests progressively "focuses in" in any way, or if each test is simply an independent event. 
20060327, 21:28  #2 
2·19·173 Posts 
..or to be more specific..
Ok maybe a better way of phrasing this is as follows: does the torture test avoid redundancy in the parameters of each test. OR is it the case that each test may or may not be redundant to some degree.

20060328, 00:41  #3 
"Mark"
Feb 2003
Sydney
3·191 Posts 
Each run of a test is the same, following a fixed sequence which eventually repeats. (You can choose different types of test & parameters, but that's a different story.) Ten hours should be longer than the sequence, so 2 * 10 = 20, near enough, but 2 * 1 is not the same as 2.

20060328, 00:47  #4  
"Richard B. Woods"
Aug 2002
Wisconsin USA
2^{2}×3×641 Posts 
Quote:
Quote:
Quote:
A torture test runs a certain number of LL iterations on each of many different exponents (actually, Mersenne numbers with different exponents, of course). The table of test exponents (and the corresponding correct answer for each one) is fairly long  many dozens of different exponents, covering a wide range. I think it may take more than 24 hours to cycle through the complete set of test exponents on at least some systems, so letting the torture test run for long periods is the best way to push as many different bit patterns through as possible, so as to maximize the probability of hitting upon a pattern that is defectively processed. 

20060328, 07:43  #5 
13·41 Posts 
Thanks
Awesome. Thanks all.

20060812, 05:22  #6 
3×29×31 Posts 
Another question: What parts of the CPU are and aren't tested? I'm using the program to test a heavily overclocked Prescott CPU. When I push it too far, I start getting "rounding errors, expect < 0.4". Upping the voltage makes it good for a few more bus clicks, etc.
My question is: What does this error mean, exactly? What kinds of instructions are failing? Are there other electrical pathways in my CPU that could be faulty that prime isn't testing properly? 
20060812, 12:45  #7 
P90 years forever!
Aug 2002
Yeehaw, FL
17×19×23 Posts 
The error means that some floating point instruction returned a bad result. Prime95 does a great job at testing your floating point unit, L1 and L2 caches, and main memory. If the "weakest" spot in your systeem is somewhere else, then another program might fail before prime95 does. That is why you should run a variety of test programs before calling your machine stable.

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