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Old 2019-04-18, 22:58   #7
kriesel
 
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"TF79LL86GIMPS96gpu17"
Mar 2017
US midwest

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Default Why don't we run lots of really old computers, on individual assignments each?

Two reasons, time and money. A sufficiently old slow computer or other device will not complete the task before the assignment expires or the hardware fails. A sufficiently old device will use exponentially higher electrical cost per unit of progress made. It's actually more cost effective to buy newer hardware than to use very old free hardware. It's like an old car with little value, that costs too much to operate or maintain. A recent check I ran briefly showed for p=77232917, on a Windows NT 4 pentium 133 with prime95 v24.14, the latest version that would run on it, 16.5 seconds per iteration, while the system consumed 60 watts. That extrapolated to a cost per 85M primality test of over US$3000 for electricity at $0.12/kwhr, and a run time of 44 years. But note that the upper limit of that version of prime95 is around 79,300,000, well short of the current GIMPS wavefront for first-time primality tests. It would also be a cost-prohibitive way of running LL double checks.

On the other hand, lots of power-efficient slow computing devices may be useful. See the effort to bring low cost damaged cell phones into the fray. https://www.mersenneforum.org/showthread.php?t=23998


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Last fiddled with by kriesel on 2019-11-19 at 15:52
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