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Pretty simple question. Is there any hardware for desktop PCs that allows you to add more DIMMs to the bus? I have seen this hardware for more expensive servers, but wondered if there was a similar setup that would be more cost efficient.

On a related question, if there is a limitation to the number of memory modules a computer can have, is it dependent on the CPU? I am thinking back to when I dealt with a dual Xeon processor workstation a while back and it had 3 DIMM banks for each CPU.

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I haven't heard of Memory expanders for desktop-class memory, and I haven't delved into server CPUs/architectures too much.

Desktop memory is usually capped by the CPU and/or the motherboard's northbridge, depending on the exact generation (Core i7 and later have the memory controller built into the CPU, for example, while earlier generations have it built into the motherboard's northbridge).

Some small form factor motherboards might not have the maximum slots due to size limitation, but if you browse the high-end ($200+) motherboards on Newegg for a given processor type, you should be able to pretty quickly find the maximum supported memory. Most desktop class CPUs currently available will max out at 2 slots per memory channel. You could in theory have a piece of hardware which joins two sticks of memory which are each half of a slot's maximum, but it would be slow, and not cost effective. The cost effective method would be to buy a motherboard which supports the maximum number of slots for that CPU.

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Taking a look myself at the high end motherboard limitations it looks like its pretty decidedly 32GB. I may have to do some research on the memory capacity for different CPUs. Might land me in Xeon and the equivalent AMD processor territory. –  Stephen R Jan 28 '13 at 23:54
    
The Socket LGA2011 processors from Intel can support up to 8 slots (Quad-channel) and 64GB of RAM on a single processor. ($250-$350 motherboard, might only be a subset of the LGA2011 processors, but at least some of them can support it.) –  Darth Android Jan 29 '13 at 5:14
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Short answer - no.

The reason that memory expansion boards you have seen in server systems were possible is that they used registered memory. There are no such boards for unbuffered memory. Also there is no need for it in desktop systems. Modern Intel desktop processors support up to 32 GB, many boards have 4 memory slots and 8 GB memory modules are readily available.

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I guess it is fair to say "no need" for the typical desktop use - but I was hoping to find some solution to getting a VMWare ESXi environment up and running on a dime. Guess I won't be able to cut corners in this one :/. –  Stephen R Jan 28 '13 at 23:52
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Short: No, you will not find any.

Long answer: Most memory controllers can only control a limited number of memory ranks per channel.

Usually 2 unbuffered (normal consumer) DIMMs per channel, or 3 buffered/registered DIMMS per channel. And since registered DIMMS buffer the output they are always slower by at least one cycle. As a result they only get used in servers where more bit slightly slower memory is preferred over less but faster memory.

If you need this memory capacity you will either: Get a motherboard, a CPU and a memory which is buffered. Or get a CPU and motherboard with more memory channels (e.g. i7 920 series with 3 memory channels and thus up to 3x2 DIMMS. Or find some rare (and expansive) low load DIMMs, get lucky and have a motherboard which supports that.

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