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5,1 MP RAM Upgrade - Getting 1333MHz speeds out of chips stuck at 1066Mhz!

handheldgames

handheldgames

macrumors 68000
Original poster
Apr 4, 2009
1,943
1,171
Pacific NW, USA
In March 2012, I upgraded my MacPro from 16GB @ 1333Mhz (4x4GB OWC ECC RAM) to 32GB @ 1066Mhz(4x8GB G.Skill non-ECC ram). Whilst the boost over 16GB helped my workflow from hitting the VM, I was never happy with the drop in RAM speed. Resetting the SMC/PRAM has no effect on getting the speed back to 1333Mhz. While the ram could easily be clocked to 1333Mhz in a PC using manual controls, it was a no-go on the 5,1.

Today, with a loss of 8GB, I was finally able to run 24GB @ 1333Mhz by dropping a 240-Pin DIMM from Slot #4(closest to the heat sync). Apparently slots 1 & 4 share bandwidth and adding chips from most vendors slows the bandwidth to 1066Mhz. From my findings, OWC/MacSales chips run fine in 4x 1333Mhz specs.

So if you are running 32GB @ 1066Mhz and want a boost to 1333Mhz and can handle loosing 8GB without a slowdown, this is your chance to gain back a few percentage points in lost performance.
 
666sheep said:
This is (very) old news :)
https://forums.macrumors.com/threads/992738/

BTW, bank 4 shares bandwidth with bank 3, not 1. Same with DP boards (bank 3 & 4 and 7 & 8). That's why you can't place DIMM in slot 4 when slot 3 isn't occupied (same with 7 & 8).
http://macs.about.com/od/macupgrades/qt/2009-2012-Mac-Pro-Memory-Upgrades.htm

Real world performance difference isn't noticeable in most task.
Click to expand...

Thanks for pointing out the legacy post. Quickly going through it, it wasn't apparent that dropping down to 3 sticks delivers 1333Mhz for ram, although it may be in there somewhere.

What did stand out was:

"So on the Mac Pro there are two controllers attached to one bank/slot each and one controller that is attached to two banks/slots.

----- memory controller 1 --- [ 1 ] --- [ 4 ]

----- memory controller 2 --- [ 2 ]

----- memory controller 3 --- [ 3 ]"
 
handheldgames said:
"So on the Mac Pro there are two controllers attached to one bank/slot each and one controller that is attached to two banks/slots.

----- memory controller 1 --- [ 1 ] --- [ 4 ]

----- memory controller 2 --- [ 2 ]

----- memory controller 3 --- [ 3 ]"
Click to expand...

Yeah, I've seen that. But article I linked states otherwise (what seems more logical to me than deconstruct's quote, due to necessity of population 3rd slot when you want to populate 4th - you'll find it in Apple memory configuration guides, in service manual as well).

Single-processor model

Slot 1: Memory Channel 1
Slot 2: Memory Channel 2
Slots 3 & 4: Memory Channel 3
Click to expand...
 
Last edited:
Can you post the part numbers of your G. Skill DIMMs please or at least say if they are 1.35V rather than 1.5V.
 
Strange that they didn't work at 1333MHz then.

Other's have had this issue though, even with just 3xDIMMs and an i7. There isn't any documentation for using i7s on the 5520 chipset though as Apple are the only ones who used it for single CPU systems. So while one might expect them to work like a Xeon W3600 does in the Mac Pro or on a regular consumer/enthusiast board with the X58 chipset there is no guarantee.

I like to optimise my memory placement and get the bet performance, but honestly as long as you don't gimp it with weird placements I wouldn't worry about minor differences, like the speed between 1066z and 1333MHz or going from triple channel to the interleave you get with 4 DIMMs on a Mac pro.

Capacity is king ;)
 
I'm on my 2nd i7 CPU in a 4,1 upgraded to a 5,1 and have and 0 issues with the CPU or RAM. When I initially upgraded to an i7-975, there were a some here at MR that had issues using this CPU, RAM or otherwise. Jumping to a 990x was just as easy.

FWIW, I would put any blame on an i7-975, 980x or 990x not working in a 4,1/5,1 on bad silicon or improper installation and not compatibility. My system runs with 1,2,3 or 4 Dimms. :cool:

Umbongo said:
Strange that they didn't work at 1333MHz then.

Other's have had this issue though, even with just 3xDIMMs and an i7. There isn't any documentation for using i7s on the 5520 chipset though as Apple are the only ones who used it for single CPU systems. So while one might expect them to work like a Xeon W3600 does in the Mac Pro or on a regular consumer/enthusiast board with the X58 chipset there is no guarantee.

I like to optimise my memory placement and get the bet performance, but honestly as long as you don't gimp it with weird placements I wouldn't worry about minor differences, like the speed between 1066z and 1333MHz or going from triple channel to the interleave you get with 4 DIMMs on a Mac pro.

Capacity is king ;)
Click to expand...
 
handheldgames said:
I'm on my 2nd i7 CPU in a 4,1 upgraded to a 5,1 and have and 0 issues with the CPU or RAM. When I initially upgraded to an i7-975, there were a some here at MR that had issues using this CPU, RAM or otherwise. Jumping to a 990x was just as easy.

FWIW, I would put any blame on an i7-975, 980x or 990x not working in a 4,1/5,1 on bad silicon or improper installation and not compatibility. My system runs with 1,2,3 or 4 Dimms. :cool:
Click to expand...

I wasn't saying anything different, the issue I was referring to with i7s was the same memory speed issue you are having. I.e some people couldn't get 1333MHz with just 3 DIMMs.
 
Thanks for pointing that out. Unfortunately the 2nd Generation MP lacks badly needed controls over memory speed other than auto-detection. The G.Skill RAM runs great in my x58 based mackintosh sitting next to the pro.

I'll be definitely putting the extra 8GB back into run as my development RAM disk, the speed makes one helluva performance jump over a xp941 Flash based boot disk.


Umbongo said:
I wasn't saying anything different, the issue I was referring to with i7s was the same memory speed issue you are having. I.e some people couldn't get 1333MHz with just 3 DIMMs.
Click to expand...
 
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