What RAM can/can't I put in my 4,1>5,1? (details inside)

[ithinkitsnice]

I have a MP4,1 flashed to 5,1 (W3690), currently with 16GB (4x8GB) of DDR3 ECC 1333MHz modules.

16GB was a decent whack way back when I stuck that in but obv not so much now, so I'm looking at swapping out 2x4GB modules for 2x8GB. I did a search for "DDR3 ECC 1333MHz 240pin" but there still seems to be things I don't quite follow.

The vagaries of UDIMM, RDIMM, ECC, non-ECC etc are beyond me. I can see what I reckon must be compatible here, but I'm also not sure about the effects of mixing modules. For example, I think I cannot mix ECC and non-ECC, but I'm not sure.

Can somebody give me a quick summary of what I can and can't do?

 

[h9826790]

You can mix ECC with non-ECC, result, ECC will be disabled.

You CANNOT mix RDIMM with UDIMM, this is a straight rule to follow. If you only want to swap 2 sticks out, you have no choice but only buy RDIMM or UDIMM according to the RAM remaining in your Mac.

You can mix the 1333 RAM with 1600 RAM or 1066 RAM etc, result, all RAM will follow the lowest speed RAM, and run at the lower speed (assuming the CPU etc is OK for that speed).

 

[kohlson]

I did some work with a hardware vendor and Intel around this time. If I recall correctly, some of these CPUs wanted memory in triples for optimum performance. That's why the standard/base config was 6GB (3x2). The is a slight performance penalty for not configuring accordingly (5%-ish - memory read, not end-to-end). And, any performance hit is very much outweighed by memory contention - swapping to VM. Remember that these are server CPUs, and meant to go in tuned configurations. I suspect your usage doesn't fit this criteria. I mention all this because it can contribute to some of the understanding, and misunderstanding, of adding memory to Mac Pros. Note that I have 4x2GB in my 4,1. Also, good advice from h9826790.

 

[ithinkitsnice]

You can mix ECC with non-ECC, result, ECC will be disabled.

You CANNOT mix RDIMM with UDIMM, this is a straight rule to follow. If you only want to swap 2 sticks out, you have no choice but only buy RDIMM or UDIMM according to the RAM remaining in your Mac.

You can mix the 1333 RAM with 1600 RAM or 1066 RAM etc, result, all RAM will follow the lowest speed RAM, and run at the lower speed (assuming the CPU etc is OK for that speed).

Exactly what I was after, thanks.

How can I tell if I've got RDIMM or UDIMM? These are my modules (which my system profile says are running at 1333MHz oddly)

http://eshop.macsales.com/item/OWC/85MP3W4M16GK/

 

[ActionableMango]

How can I tell if I've got RDIMM or UDIMM?

I'm not aware of a way to tell in OS X. But you can do a search on the memory stick's model number for the specifications and it will say which it is.

Registered/Buffered are RDIMM
Unregistered/Unbuffered are UDIMM

 

[h9826790]

Exactly what I was after, thanks.

How can I tell if I've got RDIMM or UDIMM? These are my modules (which my system profile says are running at 1333MHz oddly)

http://eshop.macsales.com/item/OWC/85MP3W4M16GK/

I will ask OWC. Even though they may be wrong, but the chance you can get the correct answer still quite high. And then do some research on Google with that part number as a double confirmation. Then you should have 99.9% chance get the right stick.

 

[MacUser2525]

Exactly what I was after, thanks.

How can I tell if I've got RDIMM or UDIMM? These are my modules (which my system profile says are running at 1333MHz oddly)

http://eshop.macsales.com/item/OWC/85MP3W4M16GK/

Those are not the modules you have unless OWC is in the habit of selling non certified ram ie. higher specifications at lower speeds. Now looks like you want to go to 24gb in that case go with three x 8gb to take advantage of the triple channel. Mixing and matching the two x 4gb with two x 8gb although in theory should work does not always work out well. In addition to the u/rdimm idea you need to look out for high/low density ram as well. Best off just going with the three x 8gb matched sticks from the start to eliminate all the foolishness that is in the ram business knowing they will work together. Oh as well then there is the double sided/single sided foolishness to look out for as well, in short matched set eliminates this.

 

[kschendel]

I agree, unless you need to pinch pennies, just toss what's in there and buy 3 x 8gb. I got mine from Data Memory Systems ( http://www.datamemorysystems.com/dm61-769-x-3/ ), I'm sure there are plenty of other good vendor choices as well.

 

[ithinkitsnice]

Those are not the modules you have unless OWC is in the habit of selling non certified ram ie. higher specifications at lower speeds.

I'm certain they are the modules I have.

I was basically just looking for the most economical upgrade. I'm on a budget and I'm the UK, RAM costs a bit more here than the states and if I ship from the states I get a VAT bill for 20% on landed cost from the taxman.

Think I'll just hold off a bit until I can spare enough for 32GB in one go, which is what I was aiming for ultimately.

Thanks.

 

[scott.n]

Used RAM pulled from servers is a great budget option. Take a look on eBay.

 

[MacUser2525]

I'm certain they are the modules I have.

Well one set has heatsinks the other bare ram so they are not the same, model name may be the same that is it. In my experience the ones with the heatsinks are usually the high density ram non-compatible with the ram without the heatsinks type. If you were to take them covers off most likely you would see dozen or more chips on them. An example below of the many chip ram usually hidden beneath the heatsink type I speak of.

http://www.ebay.com/itm/New-8GB-2Rx...895925?hash=item566cf09e35:g:cXoAAOSwBLlVbuJB

 

[ithinkitsnice]

Well one set has heatsinks the other bare ram so they are not the same, model name may be the same that is it.

"Memory modules may differ in appearance from those pictured."​

The modules in the photo have got a different model number to what's listed on the page. It's just a generic illustration.

The modules listed on the page are the modules I have.