20101019, 23:40  #1 
Jun 2010
Pennsylvania
13·71 Posts 
Whither Older CPUs?
The PC I'm contributing to OBD has been taking a number from 70 to 73 bits, and at current rates I estimate that it will take approximately five weeks (35 days) to complete that assignment.
Now that OBD appears to have run out of exponents at the sub70 bit level (http://www.moregimps.it/billion/expo_i.php?id=bit_depth), taking an exponent upward from the current levels will start to take considerable amounts of time for CPUs featuring subGHz clock speeds. My rough calculations suggest that it'll take 20 days for my 400MHz Pentium II to go from 72 to 73. If I understand this correctly, each new bit level takes roughly twice as long to complete as the previous one  meaning that, as we move beyond the 73 level, going from 74 to 75 could take my PC close to three months to finish, and 75 to 76 would take more than five months. The issue originally arose for me the last time I finished an assignment, when I thought about taking an exponent from 80 bits to 81 so that OBD could proclaim reaching Level 15. But if my calculations are at all close to the mark, it would take my PC more than six years to complete the task! My numbers are in all likelihood off to some degree as these are impressionistic estimates, but I doubt that they're far off enough to fundamentally affect the issue: What (if anything) will the lengthening timetocompletion mean to those of you (us) who are dedicating older CPUs to OBD? Rodrigo 
20101020, 05:10  #2 
6809 > 6502
"""""""""""""""""""
Aug 2003
101×103 Posts
2^{4}×5×103 Posts 
I might be able to sneak you the status of some exponents that are above the current range. They should be at much lower bit levels. Once you have done some, you can forward the results to Luigi. Then when a new area is opened, they will have been factored to some depth greater than the starting depth. PM me if Luigi hasn't opened up a new range. Most of the exponents that remain are at 60 bits.

20101020, 11:19  #3  
Aug 2009
Ontario, Canada
3·43 Posts 
Quote:
I have been playing in the 3,321,935,*** range. I plan to send some result to Luigi in the next week or two. Grant. 

20101020, 12:05  #4  
6809 > 6502
"""""""""""""""""""
Aug 2003
101×103 Posts
2^{4}·5·103 Posts 
Quote:
http://www.mersenneforum.org/showpos...9&postcount=36 Last fiddled with by Uncwilly on 20101020 at 12:05 

20101020, 15:12  #5  
Jun 2010
Pennsylvania
1110011011_{2} Posts 
Quote:
This sounds very good, thanks. Rodrigo 

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