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Maximum - Absolute maximum memory in 6 core Mac Pro

A

All Taken

macrumors 6502a
Original poster
Dec 28, 2009
790
13
UK
What is the maximum memory in a 6 core 3.33Ghz Mac Pro? I keep seeing 48GB being tossed around.

I currently have 2x16GB DIMMS and wanted to add another 2 giving me 64GB

So what is the bleeding edge max? If you give me Apples maximum RAM figure I'll slap you.
 
All Taken said:
What is the maximum memory in a 6 core 3.33Ghz Mac Pro? I keep seeing 48GB being tossed around.

I currently have 2x16GB DIMMS and wanted to add another 2 giving me 64GB

So what is the bleeding edge max? If you give me Apples maximum RAM figure I'll slap you.
Click to expand...
48GB. You can find specs on all Apple products, including maximum RAM:
 
GGJstudios said:
48GB. You can find specs on all Apple products, including maximum RAM:
Click to expand...

Excellent, thank you for a very informative answer, how does my particular model handle memory above 48GB? Does it simply not register the extra memory or does it show but is not ever accessible in use?

Can Windows access more than 48GB on my model?

My Processor is the bottleneck here isn't it?
 
All Taken said:
Excellent, thank you for a very informative answer, how does my particular model handle memory above 48GB? Does it simply not register the extra memory or does it show but is not ever accessible in use?
Click to expand...
I haven't tried it, but I'm guessing it wouldn't even show memory in excess of the max. It might show it in System Profiler, but not in Activity Monitor.
All Taken said:
Can Windows access more than 48GB on my model?
Click to expand...
It depends on the version of Windows you have installed. For example:

http://en.wikipedia.org/wiki/Windows_7#Physical_memory_limits
 
GGJstudios said:
I haven't tried it, but I'm guessing it wouldn't even show memory in excess of the max. It might show it in System Profiler, but not in Activity Monitor.

It depends on the version of Windows you have installed. For example:

http://en.wikipedia.org/wiki/Windows_7#Physical_memory_limits
Click to expand...

What I mean to ask is if my version of Windows supports 96GB of RAM for instance then would the Mac Pro allow Windows access above 48GB? I'm pretty sure the processor limits the memory but I could be wrong.

One last question:

If I have two Apple 5770's installed in the 16x slots this will cover up the third slot from the bottom as the height is restricting access. If I wanted to use an 8x third party RAID card could I theoretically utilise the combined bandwidth of the top two PCI-e slots? I could only plug the card into the top slot as that would be the only one free but would the Mac Pro allocate 8x bandwidth to that slot with the third from the bottom being empty?

Thanks
 
All Taken said:
... . I'm pretty sure the processor limits the memory but I could be wrong. ... .
Click to expand...

Intel's Ark [for Intel-Xeon-Processor-W3580-8M-Cache-3_33-GHz-6_40-GTs-Intel-QPI] says: "Max Memory Size (dependent on memory type) Max memory size refers to the maximum memory capacity (in GB) supported by the processor." OWC says: "**Current Mac OS X versions are unable to utilize more then 96GB RAM due to an operating system limitation. 128GB can be fully utilized by a 2009-2010 Mac Pro if running Bootcamp with 64-bit versions of Windows XP and later as well as with 64-bit versions of Linux." So I surmise that you can put, at least, up to 64 gig (16 gig x 4 slots) in a W3580 system running a 64-bit version of Windows, but I would recommend that you call OWC [ 800.275.4576 ] just to be sure because of a note that they have under the 16x4 configuration [ http://eshop.macsales.com/shop/memory/Mac-Pro-Memory#1333-memory ].
 
Last edited:
The issue is a strange one because OS X can address 128GB of RAM.

My guess is an issue arises when using four quad-ranked DIMMs per CPU with the Mac Pro firmware. We've seen issues of a DIMM not being acknowledged when doing this with 4GB and 8GB quad-ranked DIMMs. OWC's are almost certainly quad-ranked due to when they started selling them.

If you want to try 64GB I would recommend you buy four 16GB dual-ranked DIMMs.

Such as this: http://www.superbiiz.com/detail.php?name=D3-16R16GS

If you do please let us know whether it works or not.
 
Currently I'm running 2 x 16GB dual rank 1333Mhz ECC DIMMS. I'm tempted to buy another 2 to test but wonder if it would fail. The DIMMS i'm using are not quad ranked so I won't have a down clock issue.

Let me get this straight, can OSX on my machine see more (and use more) than 48GB? Is this number confirmed?
 
All Taken said:
Currently I'm running 2 x 16GB dual rank 1333Mhz ECC DIMMS. I'm tempted to buy another 2 to test but wonder if it would fail. The DIMMS i'm using are not quad ranked so I won't have a down clock issue.

Let me get this straight, can OSX on my machine see more (and use more) than 48GB? Is this number confirmed?
Click to expand...

The only confirmation is that OS X can address at least 128GB. No one seems to have tried what you want to do. I'd find somewhere with a good return policy and try it out if you want 64GB.

edit: didn't even notice you were in the UK. Just buy and return under the distance selling laws if it doesn't work.
 
Umbongo said:
The only confirmation is that OS X can address at least 128GB. No one seems to have tried what you want to do. I'd find somewhere with a good return policy and try it out if you want 64GB.

There is no reason for OS X on your system to be unable to address 64GB of RAM, when it can on others.
Click to expand...

It's been noted above that OWC have tried, does anyone know if 48GB was the maximum?
 
All Taken said:
It's been noted above that OWC have tried, does anyone know if 48GB was the maximum?
Click to expand...

They tried with quad-ranked DIMMs and couldn't get it to recognize all of them in OS X so 48GB has been listed as the maximum working memory on a single CPU Mac Pro.

Because 64GB certainly works only dual-CPU systems and can be addressed by the OS, it is surely some issue with the DIMMs used and memory configuration rather than the OS capping it at 48GB. Whether the solution is to use dual-ranked DIMMs I don't know, but it would certainly be what I would try first. Especially as you can return them within 7 days here in the UK and because people had the same issue with lower capacity quad-ranked DIMMs not all being recognized when all memory slots were full.

Maybe someone will chime in saying they got it working, but I've never seen anyone say they have so far.
 
Umbongo said:
They tried with quad-ranked DIMMs and couldn't get it to recognize all of them in OS X so 48GB has been listed as the maximum working memory on a single CPU Mac Pro.

Because 64GB certainly works only dual-CPU systems and can be addressed by the OS, it is surely some issue with the DIMMs used and memory configuration rather than the OS capping it at 48GB. Whether the solution is to use dual-ranked DIMMs I don't know, but it would certainly be what I would try first. Especially as you can return them within 7 days here in the UK and because people had the same issue with lower capacity quad-ranked DIMMs not all being recognized when all memory slots were full.

Maybe someone will chime in saying they got it working, but I've never seen anyone say they have so far.
Click to expand...

I'll buy a couple more 16GB DIMMS and let you know, or, you could test it first? ;)
 
Unless someone can convince me otherwise, cheaping out on ram considering OWC's fantastic service would be really reckless for me if the ram goes bad on a day I am supposed to be billing out 2-3 grand for a shoot.
 
Macshroomer said:
Unless someone can convince me otherwise, cheaping out on ram considering OWC's fantastic service would be really reckless for me if the ram goes bad on a day I am supposed to be billing out 2-3 grand for a shoot.
Click to expand...

The RAM is as reliable as every other main brand, Crucial to name one. Many offer lifetime warranty anyway unless in Russia. Don't kid yourself with OWC RAM it's seriously over priced and no more reliable.
 
Well in my opinion most ram has a lifetime warranty, for a reason. It is comparable or not, it works or doesn't, I haven't heard of ram failure to be honest, there probably are cases but well I havent heard or read about them. After following owc's pricing over the holidays I also think they are all about their own branding and overpriced, their non-existent (although well advertised) sales tells me they are all about themselves and that's not for me (their ssds priced in their winter catalogue were actually cheaper than their web prices...when I enquired they would not honor their catalog prices.)
 
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