Hypothetical Build

[Kevin]

I don't really have the money or space for dedicated crunching machines, but sometimes I like to pretend I do (or at least be prepared in case I come across a sizable sum of money). I'm fairly certain that having multiple cheap quad-core desktops gives you the best bang for your buck (at least with respect to GIMPS crunching), but I check every so often to see how close multi-processor server configurations can get. For example, on Newegg right now you could build a rackmount server with 4x2.3ghz quad-core Opterons, and 16x2GB DDR2 800mhz ECC registered memory for a little under $2000 (maybe less if I took the time to shop around at difference places).

Ignoring the cost differences, how would a server like that perform compared to having the processors/memory spread evenly across 4 different boxes?

[potonono]

Weird coincidence, but I've been pricing a PC for my wife and had come up with the following:

Intel motherboard bundled with Intel Core 2 Quad 2.33GHz - $300
4Gb DDR3 1033 Mhz - $60
550 watt power - $60
Mid tower case - $50
Tax - $30
(no hard drive - I already have plenty)

I would also get one or more nice video cards, but for a number cruncher, those could be left out. With faster memory and better processor, I think four of these would beat out any similar opteron server.

As for just having similar equipment spread out in separate boxes as opposed to just one big box, I assume performance differences would be based on how well the memory is or isn't shared (likely with the big box at the disadvantage).

[Kevin]

Originally Posted by potonono

Weird coincidence, but I've been pricing a PC for my wife and had come up with the following:

Intel motherboard bundled with Intel Core 2 Quad 2.33GHz - $300
4Gb DDR3 1033 Mhz - $60
550 watt power - $60
Mid tower case - $50
Tax - $30
(no hard drive - I already have plenty)

I would also get one or more nice video cards, but for a number cruncher, those could be left out. With faster memory and better processor, I think four of these would beat out any similar opteron server.

As for just having similar equipment spread out in separate boxes as opposed to just one big box, I assume performance differences would be based on how well the memory is or isn't shared (likely with the big box at the disadvantage).

I know that just based on performance for GIMPS, separate computers is the best, but there are other factors that might push someone towards what I'm looking at. It takes up a lot less space, doesn't use nearly as many cables, might use less electricity because of fewer peripheral devices, easier to manage one machine vs four. Maybe you have other computing needs that are multithreaded and scale well past 4 cores. Not to mention the sex appeal of having a 16 core machine. I know I'm going to be moving around a lot over the next decade, generally between places without a lot of space, so having a large fleet of desktops (or even a bunch of headless single-socket desktop boards in a homemade server rack) isn't really an option.

My guess would also be that memory contention is more of an issue, but maybe quad-channel memory or better memory controllers on servers/Opterons would reduce the effect. Even if it is more of a problem, it would be nice to know if it's in the ballpark of an extra 5% performance hit or 50% performance hit.

[fivemack]

You have forgotten that you need Opteron 8xxx CPUs to run a four-CPU configuration, and the cheapest of those are $700 each

[Kevin]

Originally Posted by fivemack

You have forgotten that you need Opteron 8xxx CPUs to run a four-CPU configuration, and the cheapest of those are $700 each

I thought I checked that, but apparently not. I think I assumed all of the Shanghai cores were 8xxx but never actually looked at the numbers after I restricted my search. Well that puts a damper on things...