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Does Prime95 use multiple cores? (Is there a difference in this regard between running it from Windows, UBCD, or UBCD4Win?)

If it doesn't, are there tools out there that will (preferably via a boot disc)?

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up vote 4 down vote accepted

Yes Prime95 utilizes multiple cores. Just turn up the 'thread count' option to at least as many cores as you'd like to test.

As long as the OS you choose to run it on sees your multiple cores, Prime95 should use them.

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@techie007: So, does it do this from a boot disc as well? Say, UBCD4Win? Thanks! – ssvarc Mar 14 '10 at 19:42
NP, just ensure you have a newer UBCD, built with at least XP SP2 and a newer Prime95 ( and you should be good. :) – Ƭᴇcʜιᴇ007 Mar 14 '10 at 19:50
@techie007: UBCD or UBCD4Win? (The two are not the same. Your using the build method for UBCD4Win [I think] and the UBCD name.) Thanks! – ssvarc Mar 14 '10 at 20:05
@Ssvarc According to the UBCD homepage (, UBCD still uses v23.5.2 of Prime95, which does not have built-in multi-threaded support. – sblair Mar 14 '10 at 20:27
@Ssvarc - I was referring to UBCD4Win - Sorry. :) UBCD4Win has Prime95 v25.8.3.0 as of v3.50 (4/21/09). Plus you should be able to build v25.9 into it if needed. – Ƭᴇcʜιᴇ007 Mar 14 '10 at 20:37

When running a torture test in a recent version of Prime95, the Number of torture threads to run can be varied. I believe it defaults to the number of CPU cores on the machine.

Prime95 options

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