64GB RAM in a Quad-Core Nehalem?

I have a dual CPU Mac Pro 2010 with 2 x X5675 chips (making it in to the equivalent of a 2012 model), so no I cannot speak of this from personal experience.

This is what the MacRumors article says -

Maximum RAM:

• 56GB in a single-processor Mac Pro using a single-processor-capable Xeon (i.e. a W chip)
• 64GB in a single-processor Mac Pro using a dual-processor-capable Xeon (i.e. a X chip)
• 128GB in a dual-processor Mac Pro (i.e. 2 x X chips)
• 48GB for a single-processor Xserve
• 96GB in a dual-processor Xserve

With my additions in parenthesises.

The same article goes on to say -

Installing a single "Dual Xeon" processor into a single-processor Mac Pro works fine, and actually increases its maximum RAM from 56 to 64GB.

From what I could find on the interwebs, the max usable memory is bound to the OS X version and the CPU.

So a single X-series CPU (not the W-series!) with Sierra should, as hear-say goes, support 64 GB.

I just upgraded a mid 2010 2.8 quad to a X5680 @ 3.33GHz (6 core) and bought a 4 x 16 GB RAM Kit from OWC.
Sadly, one of the modules fails (red LED lights up at RAM slot), so only 48 GB are available.
I can use the troubling module fine, so long as only 3 modules are inserted. As soon as I add a fourth module, the same specimen fails (red light), regardless of slot distribution.

Does that mean the 64 GB on a single cpu system are a pipe dream?

Hard to say ...but seems like a reasonable assumption.

For why it is always the same module that fails in a 4 dimm configuration,

regardless of order, no clue.

The clue is that slots 1 and 2 are independent, and 3 and 4 are shared with each other. So the bus loading (and therefore the speed at which the data can be presented) will be different for slots 3 and 4. So if things are tight, slots 3 and 4 will not BOTH be able to work. One or the other.

May well be true, but does not match my observation.

I can put the offending module in any slot ... 1, 2, 3, 4 - it is the same module that will not be recognized.
I.e. the module will work when seated in slot 1 while slot 4 is empty [|||.]

Once I add another module, the offending module is disabled [||||].

Swapping modules leads to the same result: [||||]

It sounds like that particular module may be marginal -- works sometimes, not others.

The hardware suggests that slot 3 or 4 would be the one to not work properly with all four present.

But keep in mind, the Error Correction Code circuitry in the Xeon processor is used very aggressively at Startup. ANY error, correctible or not, that occurs in those few seconds of the Power On Self Test will cause the modules to be tagged as "do not use" and its slot declared "empty".

In re-reading my previous posts, i see that I did not state strongly enough:

If you install three 16GB modules, including the one you called the "offending" module, into slots 1, 2, and 3, and leave slot 4 empty, any that are rejected by the Power On Self Test are BAD, and should be returned to the Vendor for refund or replacement.

If you run the test again, that module may test OK, but that does NOT make it good. If it fails, ever, it is Bad, unless you have another reason to give it a break such as the machine was red hot after hours of testing with the door off.

Not sure how to put this more clearly than this:

I can confirm your claim that only 3 x16 GB modules can be used concurrently. What I can not confirm from observation is this:

Grant Bennet-Alder wrote:

slot 3 or 4 would be the one to not work properly with all four present

It is always the "weak" module that gets disabled, regardless of which slot it is seated in. If I put it in slot 1, slot 1 will be the one to fail (with all four being used). Removing any other module (so that max. 3 are used), the "weak" module works fine, again, regardless of which slot it is seated in.

In any case, thanks for chiming in 🙂

Oh, I see now. That is a bit more complicated. If I am understanding you correctly, the offending module is the one that fails whenever FOUR are present (and not otherwise) regardless of which slot it is placed in.

Perhaps the signal drivers on that module are a little weaker than its cousins in other slots, and it gets overpowered by them. Four modules present also changes the timing ever-so-slightly, and may make a marginal module stop presenting its data in time to be seen correctly.

You may want to contact OWC (presuming it is their modules) and ask them about that. If this is "expected behavior" (likely due to random variability in modules), they will tell you so, and if it is not, they may want to send you a different module to try.

Regardless, they seem to be very generous with their help.

The official Apple limit was 32GB i.e. 4 x 8GB for the single CPU model. As other have indicated according to OWC and I also found EveryMac the unofficial limit is 48GB via 3 x 16GB DIMMS.

The reason the dual CPU model can not merely do 96GB i.e. double 48GB but is actually able to do 128GB is as already pointed out by cj-locale down to the fact that all dual CPU models use the X series chips, whereas the single CPU models use the W series chips. Whilst a quad core Mac Pro would normally have a W series chip it is possible to fit a single X series chip in to it and it will work and then would allow using 64GB i.e. 4 x 16GB.

I believe your quad core Mac Pro would have a W3570 chip i.e. the single CPU model which cannot support 64GB. The X5672 would be the nearest dual CPU compatible chip and could be fitted in your Mac Pro and would then allow 64GB.

According to this https://forums.macrumors.com/threads/mac-pro-cpu-compatibility-list.1954766/ the single CPU i.e. quad core Mac Pro can actually do 56GB, I would guess this is 3 x 16GB plus 1 x 8GB. I am a little dubious about this since most reports I have seen suggest mixing 16GB DIMMS with other sizes does not work. If you did want to upgrade the CPU chip in your Mac Pro the same macrumors article lists all the known compatible chips.

Note: The Mac Pro 2010 and Mac Pro 2012 are both listed as MacPro5,1 model and in reality the Mac Pro 2010 and 2012 are identical. The only difference is that the Mac Pro 2012 shipped with faster CPU chips as standard compared to the 2010. It is possible to swap the CPU chips in a 2010 to the same ones used in the 2012 and it then literally is 100% identical in specifications.

John Lockwood wrote:

I believe your quad core Mac Pro would have a W3570 chip i.e. the single CPU model which cannot support 64GB. The X5672 would be the nearest dual CPU compatible chip and could be fitted in your Mac Pro and would then allow 64GB.

Do you know this from first hand experience?
My Mac Pro 5,1 (2010) is fitted with a X5680 and has trouble with 64 GB, as previously described.

If you can confirm that single cpu systems with X-series support 64 GB, that sounds like I need to talk to the RAM vendor 🙂

48 GB is pretty beefy; depends on what you do with your system, but do you really need more than that? I guess if you need to run multiple virtual machines and assign all of them hefty chunks of RAM, then you might run out of headroom.

The 2010 Mac pro (5.1) one cpu models cam take up to 64 gb, the two cpu models up to 128gb with 16 gb modules.

So i am pretty sure your mp 2012 (four ram slots is one cpu model) can take 64 gb too.

But take care to buy the correct ram modules, the mp only takes specific modules, ask your hardware dealer for correct modules.

I have the mp 2010 5.1 two cpu model running perfectly with 128gb ram.

greetings from germany

Chris

here Mac Pro (Mitte 2012 und älter): Speicher entfernen oder installieren - Apple Support you find the technical specifications.

Apple tells you that the one cpu model can take up to 32 gb, but that is why apple sold only 32 gb models. True is 64 gb for the one cpu model.

And make sure not to mix udimm and rdimm, this cannot be done!

greetings from germany

Chris

Some aftermarket Vendors have done the testing to determine whether 4@16Gb can be used, and found they can NOT. The limit appears to be 3@16GB, and you can not mix these "Registered" 16GB DIMMs with ordinary "unRegistered" DIMMs.

Look at the detailed charts provided on this page for reference:

https://eshop.macsales.com/shop/memory/Mac-Pro-Memory#1066-memory

.

oops, what a strange limitation ➖

sorry for my false assumption