20031003, 02:21  #1 
Oct 2003
Australia, Brisbane
2×5×47 Posts 
60bit, 64 bit  what is the difference??
I am sorry if this is a really dumb question.
I have a pentium 4 2.4Ghz, with a gig of ram. From what i was reading in the forums i should have my testing above 64 bit. However, when i looked at the number that i was testing M33506581, it was doing it at 60 bit. What is the difference. How do i change it so that it is working at 64 bit. Is 64 bit the best for my computer or would something else be better. I see that some people use up to 69 bit. I am sorry for such a dumb question, i applogise, i am new. Anyway, any help would be appreciated. Last fiddled with by dave_0273 on 20031003 at 02:22 
20031003, 02:58  #2 
Sep 2002
2·331 Posts 
If you are trial factoring, the mersenne number you get is already partially tested by trial factoring upto a lower bit depth ( the high 50s or to 60 ) because no factor showed up it then is available to be factored to a some predetermined bit depth ( the size of the number determines it).
So when you start, it is at 60 it will keep going until it either finishes to the predetermined bit depth ( 69 is probably correct for a 33 million number ) or it finds a factor. For P1 factoring somebody else would have to answer. 
20031004, 02:24  #3  
"Richard B. Woods"
Aug 2002
Wisconsin USA
17014_{8} Posts 
Re: 60bit, 64 bit  what is the difference??
Quote:
The user documentation for GIMPS is about as good as computer programmers and mathematicians who are not also professional technical writers usually write. That might be sufficient if it were gathered all in one place  but it's not; it's scattered. It's quite common for newbies, and even notsonewbies, not to pick up the correct understanding of some things discussed in this forum. Quote:
But when you're assigned a LL test, trial factoring is only a small preliminary step of your total work, and it's not worth worrying about a P4's relative inefficency for the small part of the trial factoring that involves testing divisors up to 2^64. Quote:
In other words, the 60 is just a starting point, not some parameter of how the program operates otherwise. Quote:
Quote:
Quote:


20031004, 07:18  #4 
Oct 2003
Australia, Brisbane
2×5×47 Posts 
thanks alot. that has cleared a lot up for me.
i have just one other question (well for the moment, i am sure that in time there will be many many more), i have a dual cpu so i am running 2 copies of prime 95. For both i requested to work on 10,000,000 digit numbers but the programs seem to be working differently. one's output is... factoring M33506581 to 2^68 is 61% complete.... the others screen output is.... interation 517000/33376487 [1.55%] Per iteration time..... why are the two programs doing different things. i wanted to set them up the same but have i actually set them up differently??? thankyou to anyone who can help.... 
20031004, 13:33  #5 
"Sander"
Oct 2002
52.345322,5.52471
29×41 Posts 
The first one is doing trial factoring. It's currently at 61% of factoring up to 2^68.
This is the prelimanary step that cheesehead was talking about. When reaches 100% it will either start doing P1 testing to find even larger factors, or starts doing a Lucas Lehmer test. That is what the second cpu is doing. A LL test is used to determine if a number is prime or composite. 
20031004, 13:33  #6  
Banned
"Luigi"
Aug 2002
Team Italia
29·167 Posts 
The search for a Mersenne prime walks through different steps.
From Readme.txt: Quote:
HTH Luigi 

20031004, 14:21  #7 
"Mark"
Feb 2003
Sydney
1075_{8} Posts 
It is quite possible that, for the exponent that you are LL testing, the factoring stages were already done before it was assigned to you, saving you some work! That could explain why your two copies are a different stages, if you started them at the same time.
The Math section of the help in the program is good, if you want to know more about the stages each exponent goes through. markr (in Sydney) 
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