Torture test is an option in Prime95 to run a stress test of the computer. During the test Lucas-Lehmer tests are performed using exponents which are known to yield certain results. The test will use different FFT-sizes. If the calculated result differs from the known correct result then the test fails. Once all the test have been performed the test starts over again. Sometimes you have to run the test for several hours to provoke an error which will make it fail.
Each time the client program is using an FFT size not tested before it starts an hour long torture test to make sure that the computer works correctly.
Torture test on a multicore or multiprocessor computer
If you have two instances of prime95 running torture tests on a dual core using the default "Blend" setting, the first instance each will use about 3/4 of memory the system memory. The second instance will try to do the same. The end result is that only the first instance will show some progress.
To effectively stress all cores, one must use the "Custom" setting and adapt the amount of memory to share the available amount between theall the instances of Prime95.
For example suppose a system with a dualcore processor and 2GB of memory running Windows XP needing about 256MB of memory. There is 1782MB of free memory. The sum of the "Memory to use" parameters should not exceed 1792MB. One could use 891MB (half of 1782MB) in each instance of Prime95.
The explanation of undocumented features given in undoc.txt and the "Advanced Features" of the help file is no longer applicable to the current version of the program. In other words the "TortureMem=" line in prime.ini is not taken into account.