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I'm looking at building out a pretty beefy server, and I was wondering if I were to get a motherboard that supports multiple CPUs such as this one, can it run with only one or two CPUs temporarily?

I'm thinking it would be perfect if I could put off buying two or three processors for a couple of months to save money, since at first they won't be necessary.

Is this possible, or does it have to have all four processors in place to run?

Thanks

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9 Answers

up vote 8 down vote accepted

Yes :) you don't have to plug the two processors. I have the Tyan i5400xt (Xeon Harpertown) and I simply plugged the first processor for months. You don't have anything to do, the bios will see that there is only one cpu.

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Be carefull, I don't know if it's still true, but you used to have to buy a special socket insert to place on the non-used socket on some motherboards. –  Kevin Nisbet Sep 8 '09 at 15:51
    
Not on Tyan Motherboards actually, but yah, some mobo require that you disable the second socket otherwise the server won't boot up. Regarding this special socket insert I never heard of it, but yah that's not impossible (a bit weird though) that while the insert touches certain pins, the signal will be interpreted as the second socket deactivation I guess –  Razique Sep 8 '09 at 16:28
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Don't forget to account for the Memory capacity / fill pattern being different if you don't have all of the CPUs installed for certain setups. –  AJ. Sep 8 '09 at 16:52
    
@Kronick: I have a (very old) Pentium II 300 MHZ Dual CPU system here. That system came with a 'blank cpu card' that should be used when only 1 CPU was installed. I never used it though. –  Niels Basjes Sep 8 '09 at 20:34
    
The special insert was typically a bus terminator -- I remember that it was required on Intel Slot 1 (Pentium II, Pentium III) motherboards. You could get some motherboards to boot without the terminator installed, but you'd end up with stability issues. –  Ian Clelland Sep 8 '09 at 21:52
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Sure it can. My suggestion is: Don't do it. Fill it up to the limit right away.

My argument is that in general these kinds of system REQUIRE all CPUs to be 100% identical. If you wait a month too long you may very well run into the required additional CPUs no longer being available.... of being very expensive.

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Also, there's the "temporary fix" mentality which must be avoided. If growth is enough to predictably need the extra CPUs in the future, get them now. The problem with server upgrades is that they require downtime. –  Ernie Sep 8 '09 at 16:53
    
Short spurts of downtime isn't really an issue in this environment as long as it's scheduled. Cost, however, is an issue. It's a company that is almost gauranteed to grow very quickly, but intial capitol is very low (don't want to spend all of the investors money on IT stuff). Believe me, I hate the "temporary fix mentality" more than just about anyone. –  Max Schmeling Sep 8 '09 at 19:09
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Given this mentality I would recommend reconsidering what you are trying to do. Perhaps several 'small' systems can do the job just as fine when compared to a single 'big one'. Small systems are 'commodity' and are generally cheaper when compared to special multi CPU systems. –  Niels Basjes Sep 8 '09 at 20:32
    
+1, matching processors is important since slightly different revisions may have slighly different behaviors / bugs--whenever I've torn apart a professionally built multicore system the processors have sequential serial numbers. –  STW Sep 8 '09 at 21:47
    
Hmm if the small money for a second CPU is a financial problem then you have a more serious problem. I guess the Investor is FFF (Family, Friends, Fools). And i don't like this grows very quickly. Growth at the beginning is always infinite. Going from making 0 money and then earning $1 is infinite growth. Yes the second step is harder. –  Lothar Sep 8 '09 at 22:32
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Only desktop Intel/AMD stuff. On other CPU systems like Itanium you need dummy voltage regulartor modules that are put into the CPU socket.

I once (around 2003) bought a MP Board for AMD and plugged in only one CPU. Thought spend 200 Euro more and therefore have a later option (when CPU's are cheaper and my business is going) i can get double speed upgrade. Didn't work at these days as the CPU was quickly out of sale and no way to mix CPUs with different speeds.

I learned from this. Never do to provide yourself with an upgrade path. Buy now and sell it after upgrade - this saves much more money in the end.

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I have 2 HP servers here with 2 CPU socket available and running with only one CPU for 3 years now and there's nothing wrong about doing that plus it give you the possibility to add another CPU if needed at lower cost later ;)

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presuming, of course, the exact model is still available in, say, a year or 4 :) –  warren Sep 8 '09 at 16:05
    
Yes of course ;) –  Marc-Andre R. Sep 8 '09 at 18:19
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In some cases it depends on the motherboard. The mobo specs or a quick Google search should be able to tell you if the mobo is capable of running with less than the max processors.

In YOUR case, the mobo you mentioned:

Thunder n4250QE S4985-SI (S4985G3NR-SI)

Looks like it DOES WORK with less than the max processors installed. Take a look at the following links:

http://www.tyan.com/product%5FSKU%5Fspec.aspx?ProductType=MB&pid=638&SKU=600000075

http://www.tyan.com/support%5Fdownload%5Fcpu2.aspx?socketid=16

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Yes it is possible to run an empty slot. But that is an issue for the chipset that manages the onboard operations of your motherboard. The IBM P570 that I have runs with optional chips off but in place. If you want to "buy" the chips you have IBM will send you a code to activate them. You can also have the system shipped with only the chips you paid for and have nothing else in place. Same is true for HP, which I moved off of recently.

Sever companies love to be able to sell options but if you get into the grey box space it is hit or miss.

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Or what about using all dual core cpu, and then if needed, upgrade to quad? One virtue to that is more memory bandwidth, at the cost of having your memory fragmented (each socket has it's own memory bus and sockets) and perhaps needing to replace memory in the future.

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Why don't you consider buying a lower-end motherboard with enough processors to fill all slots? When you need to upgrade you can order a quad-cpu board along with matching processors and either delegate the smaller system to other tasks or sell it second-hand.

You'll save some money upfront, get a matched system when you need it, and also possibly offset some of the depreciation on the smaller board / procs with savings on the bigger board... tech gets cheaper quickly

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This was possible with server boards that I looked into.

A big downside was that with only one CPU, one half of the RAM was not usable. One half of the RAM went to one CPU and one to the other CPU.

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