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Old 2008-07-20, 18:59   #1
Jul 2008

5 Posts
Default How much memory should I dispatch?

How much memory should I dispatch to Prime95?

I have read about this in the "help" in the program, but I think that information is a bit outdated... I have 4 GB RAM, and running Vista only consumates 1-1.5 GB RAM (according to Vista).

I have recently started running Prime95 for searching for numbers, and then I dispatched 100 MB of RAM (instead of only 8).

Is there any point at going higher? I know my machine can handle 1 GB, but does this actually increase the speed?

What should I choose? I have a dual core 2.3 GHz processor.
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Old 2008-07-21, 01:40   #2
Jun 2008
Spokane, WA

2·3 Posts

It depends on what kind of work you're doing. P-1 stage 2 can pretty much use anything you throw at it (and perhaps ECM on the v5 server as well, though I may be wrong about that), so the general advice is to give it as much as you can afford, while being careful to avoid thrashing. Everyone's memory usage patterns are different, so it's hard to say exactly how much you can afford. (1.5GB would probably be my limit on a 4GB machine, but I tend to use memory quite heavily.)

From my own testing, increasing the memory does increase P-1 factoring's speed, though I don't know if there's a point of diminishing returns.

The other types of work (P-1 stage 1, LL-testing, trial factoring) aren't really affected by the available memory setting.

Important note: If you're running multiple copies of Prime95, then you want to be careful to distribute the available memory among the number of clients you're running. If you're using the multi-threaded feature of 25.x, then just assign to it whatever you choose.

Last fiddled with by Aexoden on 2008-07-21 at 01:42
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Old 2008-07-28, 03:30   #3
stars10250's Avatar
Jul 2008
San Francisco, CA

110010012 Posts
Default memory questions

I recently built a system with ubuntu and mprime. According to system monitor, it is drawing 25 Mb of ram running p1. Will it ever need more? This amount seems small. Which brings me to another there a description somewhere of what the calculation actually needs? It is hard to size a new system for cpu, bus, and ram bandwidth when the needs of the calculation don't seem to be stated. Maybe I'm just missing it. "More is better" is nice, but it seems simplistic. I don't want to build a number cruncher with capabilities that can't or won't be exploited. Even the utility of L2 cache doesn't seem to be clear, with some users reporting that larger cache runs slower. Pointers to relevant threads appreciated. I'm new to all this.
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Old 2008-07-30, 22:12   #4
patrik's Avatar
"Patrik Johansson"
Aug 2002
Uppsala, Sweden

42410 Posts

During stage 2 of P-1 it can use more. Set what you can afford to give it under Options/CPU.

First of all, stability is important. If you overclock, don't go all the way to where it becomes unstable. A single unnoticed error during the normal two-month computation can spoil all that work.

I have only used Intel processors, and for them I think CPU speed and memory bandwidth are the most important. If you run a test on each CPU core, memory bandwidth becomes even more important. I posted about this in two threads:
Importance of dual channel memory
Quad Core, post about iteration timings
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