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Old 2010-10-19, 23:40   #1
Rodrigo
 
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Default 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 sub-70 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 sub-GHz 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 time-to-completion mean to those of you (us) who are dedicating older CPUs to OBD?

Rodrigo
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Old 2010-10-20, 05:10   #2
Uncwilly
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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.
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Old 2010-10-20, 11:19   #3
gjmccrac
 
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Quote:
Originally Posted by Uncwilly View Post
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.
You may want to give him ones in the 3,321,936,*** range.

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.
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Old 2010-10-20, 12:05   #4
Uncwilly
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Quote:
Originally Posted by gjmccrac View Post
You may want to give him ones in the 3,321,936,*** range.

I have been playing in the 3,321,935,*** range. I plan to send some result to Luigi in the next week or two.
This might satisfy.
http://www.mersenneforum.org/showpos...9&postcount=36

Last fiddled with by Uncwilly on 2010-10-20 at 12:05
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Old 2010-10-20, 15:12   #5
Rodrigo
 
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Quote:
Originally Posted by Uncwilly View Post
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.
Uncwilly,

This sounds very good, thanks.

Rodrigo
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