MP 1,1-5,1 5,1 Mac Pro won’t address 1333MHz RAM

[Dwight__SCHRUTE]

Hello all! First time poster here.

I have a 2009 4,1 Mac Pro that I’ve flashed to 5,1. It has dual 2.66 X5550 quad core Xeon processors. I’ve installed 8x 4GB 1333MHz PC3 - 10600R DIMMs in it. The computer lists RAM speed as 1066MHz (and only lists 24GB).

According to Wikipedia, the X5550 does support 1333MHz sticks. I’ve reset PRAM and it didn’t do anything. Any ideas on how I can get the MP to address the faster RAM?

thank you

 

[h9826790]

Sounds like your DIMM are 4Rx4, but not 2Rx4.

 

[solaris8x86]

I had that 2.66 model. The RAM speed is not 1333 I think is normal.

 

[Dwight__SCHRUTE]

Sounds like your DIMM are 4Rx4, but not 2Rx4.

Could you expand on this?

 

[bsbeamer]

Read this:

cMP & nMP {MacPro 4,1 & 5,1} Memory Upgrade Compatibility and FAQ

Here is the start to a mega thread of memory upgrades and FAQ Please feel free to post your working configurations along with your brand and model numbers. A single W36xx CPU can support up to 56GB memory (3x16 + 8) A single X56xx CPU can support up to 64GB memory (4x16) A dual X56xx CPU can...

forums.macrumors.com

 

[JedNZ]

I just replaced the 1066MHz ram in two spare cMP 4,1>5,1 cMPs with 1333MHz DIMMs and typically on first boot up the new ram shows as 1066MHz. After doing an NVRAM reset (hold down Cmd+Opt+P+R continuously for three full restarts) and they’re now registering at 1333MHz. Have you tried resetting NVRAM?

 

[h9826790]

I had that 2.66 model. The RAM speed is not 1333 I think is normal.

Intel says it support 1333MHz DIMM

Intel® Xeon® Processor X5550 (8M Cache, 2.66 GHz, 6.40 GT/s Intel® QPI) - Product Specifications | Intel

Intel® Xeon® Processor X5550 (8M Cache, 2.66 GHz, 6.40 GT/s Intel® QPI) quick reference with specifications, features, and technologies.

ark.intel.com

Have you tried resetting NVRAM?

OP said he did that in post #1

Could you expand on this?

Check the sticker on the DIMM

 

[Monotremata]

Theres a little more to the weird memory bus architecture of the Nehalem CPU than just popping in memory and having it take off at full speed apparently.. It might even be because youre using all 8 instead of two banks of 3.
https://media.kingston.com/images/branded/MKF_102_Nahalem_Ref.pdf

 

[atonaldenim]

Could you expand on this?

Always use dual rank (2Rx4) RAM in the Mac Pro, not quad rank (4Rx4).

I don't know what that means exactly, but I've had problems with 4Rx4 RAM showing up at a slower speed in Mac Pro 5,1. When I exchanged it for 2Rx4 RAM, that worked perfectly.

 

[jscipione]

Take out DIMMs 4 and 8 (closest to CPUs) and see if the memory is listed as 1333mhz. If so, then you know that you have got quad rank memory.