2133mhz Ram Test Results

ohsnaphappy

macrumors regular
Original poster
Jan 14, 2013
238
64
There's a lot of mixed information on this forum about 2133mhz ram in the Skylake iMac.

The questions that need to be answered are:

1) Will the Skylake iMac boot and operate properly with 2133mhz ram.
2) Will 2133mhz ram run at 2133mhz in the Skylake iMac? Or will it only show as 2133 in the system profile - all the while running at 1866?

Here is a stick for consideration, at $65 it's very reasonable priced: http://www.amazon.com/gp/aw/d/B00UV...X110_SY165_QL70&keywords=Kingston+hyperx+2133

I have a Skylake iMac arriving Oct 22-27, so if no one has real test results by then, I'll volunteer to be the guinea pig for everyone. Thanks!
 

Sirmausalot

macrumors 65816
Sep 1, 2007
1,072
275
I predict it will 1. Work 2. Run at the higher speed as long as you remove the stock RAM first and 3. Make absolutely zero difference except that you'll have spent $40 you didn't need to. But I appreciate that you're willing to do it :)
 
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ericv

macrumors regular
Mar 31, 2015
151
72
Apple could be using UniDIMM technology for support ddr3 and ddr4 memory: https://en.wikipedia.org/wiki/UniDIMM
I am likely willing to try DDR4 if someone can recommend which ones to buy from Amazon or MicroCenter (I'd prefer Amazon). If they don't work, I just return them.

I've been doing a bit of research on the UniDIMM and Skylake. Seems the the memory controller in the iMac likely supports Uni-DIMM, the question might be did Apple use UniDIMM slots? Anyone know how to tell so that someone that has a new iMac and confirm?
 
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xgman

macrumors 603
Aug 6, 2007
5,052
838
DDR 4 memory has different pins. They won't fit and likley wouldn't work in the imac yet anyway. I know the 1866 me will work on the new imac at speed, but not sure about the full 2133 speed. It may be more of a question of compatibility and stability in general as some sticks will behave better than others at any speed. I chose the crucial balistix 1,866 to try. We'll see.
 
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xgman

macrumors 603
Aug 6, 2007
5,052
838
Only 1 in stock. Searching Amazon all Amazon sold 8GB 2133mhz DDR4 SODIMMs are out of stock.
Look at a pic of ddr3 and ddr4 sodimm and you will see the pins and notch placement.
 

flyespresso

macrumors newbie
Sep 25, 2015
23
14
DDR 4 memory has different pins. They won't fit and likley wouldn't work in the imac yet anyway. I know the 1866 me will work on the new imac at speed, but not sure about the full 2133 speed. It may be more of a question of compatibility and stability in general as some sticks will behave better than others at any speed. I chose the crucial balistix 1,866 to try. We'll see.
True they have different pins but there is a universal slot that will allow either DDR4 or DDR3 to work (with both their unique pin setups). See above, someone linked the wikipedia article.

Question is: Is that what Apple put in there??
 

syndr0me

macrumors regular
Sep 17, 2014
137
85
CPU will support DDR3 and DDR4, but the socket is different for each. Teardown shows DDR3 RAM which means DDR3 socket. DDR4 will be touted as a new feature on the next refresh.
 

ericv

macrumors regular
Mar 31, 2015
151
72
True they have different pins but there is a universal slot that will allow either DDR4 or DDR3 to work (with both their unique pin setups). See above, someone linked the wikipedia article.

Question is: Is that what Apple put in their??
My question exactly. Maybe someone can post a well lighted picture of their slots?
 

spanishtorero

macrumors newbie
Oct 18, 2015
17
4
Barcelona, Catalonia, Spain
DDR 4 memory has different pins. They won't fit and likley wouldn't work in the imac yet anyway. I know the 1866 me will work on the new imac at speed, but not sure about the full 2133 speed. It may be more of a question of compatibility and stability in general as some sticks will behave better than others at any speed. I chose the crucial balistix 1,866 to try. We'll see.
Correct. Due to this Intel has developed UniDIMM for Skylake processors. UniDIMM supports DDR3 204-pins and DDR4 260-pins memories.

The question is if new iMac uses this technology.
 

syndr0me

macrumors regular
Sep 17, 2014
137
85
UniDIMM appears to be a unique socket from DDR3 and DDR4, and requires special SO-DIMMS which don't seem to exist. Since it ships with DDR3, it's a safe bet that it's got a DDR3 socket.
 

flyespresso

macrumors newbie
Sep 25, 2015
23
14
CPU will support DDR3 and DDR4, but the socket is different for each. Teardown shows DDR3 RAM which means DDR3 socket. DDR4 will be touted as a new feature on the next refresh.
As stated already...
https://en.wikipedia.org/wiki/UniDIMM

This is a Universal socket that can accept BOTH DDR3 and DDR4 modules. Just because the teardown shows DDR3 RAM does not mean they aren't using a UniDIMM socket and simply shipping DDR3 installed for cost. This would also make sense as they can later on go to DDR4 without new engineering on the sockets. It is not special SO-DIMMS or modules that require UniDIMM support.

Please though, read, don't just blatantly say we are all crazy! We just need someone with the 27" to take a picture of the sockets and/or try a DDR4 module!
 

syndr0me

macrumors regular
Sep 17, 2014
137
85
UniDIMM is a SO-DIMM form factor available in two dimensions: 69.6 mm × 30 mm (2.74 by 1.18 inches) for the standard UniDIMM version (the same size as DDR4 SO-DIMMs[5]), and 69.6 mm × 20 mm (2.74 by 0.79 inches) for the low-profile version.[6][1]:28 UniDIMMs have a 260-pin edge connector, which has the same pin count as the one on DDR4 SO-DIMMs,[5] with the keying notch in a position that prevents incompatible installation by making UniDIMMs physically incompatible with standard DDR3 and DDR4 SO-DIMM sockets.
So, yeah, UniDIMM is a unique socket. This iMac has DDR3 in it, which means it's got a DDR3 socket. CPU supports DDR4 but Apple decided against it for whatever reason.
 

Sirmausalot

macrumors 65816
Sep 1, 2007
1,072
275
I am likely willing to try DDR4 if someone can recommend which ones to buy from Amazon or MicroCenter (I'd prefer Amazon). If they don't work, I just return them.

I've been doing a bit of research on the UniDIMM and Skylake. Seems the the memory controller in the iMac likely supports Uni-DIMM, the question might be did Apple use UniDIMM slots? Anyone know how to tell so that someone that has a new iMac and confirm?
I would shoot a quick note to OWC to see if they tried it. You can also study the ram they pulled out of the ohttp://blog.macsales.com/33572-owc-unboxes-tears-down-the-late-2015-27-inch-imac-retina-5k
 

syndr0me

macrumors regular
Sep 17, 2014
137
85
This is a Universal socket that can accept BOTH DDR3 and DDR4 modules. Just because the teardown shows DDR3 RAM does not mean they aren't using a UniDIMM socket and simply shipping DDR3 installed for cost. This would also make sense as they can later on go to DDR4 without new engineering on the sockets. It is not special SO-DIMMS or modules that require UniDIMM support.
My previous quote is from that same wikipedia entry. It clearly states that UniDIMM is physically incompatible with DDR3 and DDR4 sockets. It's compatible with the chips but requires a UniDIMM board with its pinout and notch.
 

ericv

macrumors regular
Mar 31, 2015
151
72
Please, read the above links, UniDIMM supports both memories, DDR3 & DDR4.
I think what he is saying and I might understand is that...

UniDIMM is a memory board specification that supports DD3 & DD4, but it comes on a 260 pin stick. The sockets would only support 260 pins, not both 260 and 204. So if the memory on the new iMac is in fact 204 pins, than DDR4 and UniDIMM likely won't work.
 
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syndr0me

macrumors regular
Sep 17, 2014
137
85
Right. UniDIMM is a NEW socket standard that supports both DDR3 and DDR4 memory chips. However its a unique socket, which means it's not compatible with existing DDR3 and DDR4 sticks that use their respective sockets. It would be compatible with DDR3 or DDR4 chips on a SO-DIMM with the UniDIMM pins and locating notch.

There isn't a universal socket that accepts DDR3 and DDR4 sticks. Since the new iMac comes with DDR3 with a DDR3 pinout (not a UniDIMM pinout) it means you can only put DDR3 in the new iMac.
 

syndr0me

macrumors regular
Sep 17, 2014
137
85
So there's 3 socket standards. None of them are cross-compatible. Those are:

DDR3 (only available with DDR3 memory chips)
DDR4 (only available with DDR4 memory chips)
UniDIMM (available with DDR3 or DDR4 memory chips)

I don't think anybody is actually shipping UniDIMM memory. The iMac ships with DDR3 memory on a DDR3 socket pinout. The iMac will only take DDR3 memory. Sorry. :( I bought one anyway.
 

spanishtorero

macrumors newbie
Oct 18, 2015
17
4
Barcelona, Catalonia, Spain
I think what he is saying and I might understand is that...

UniDIMM is a memory board specification that supports DD3 & DD4, but it comes on a 260 pin stick. The sockets would only support 260 pins, not both 260 and 204. So if the memory on the new iMac is in fact 204 pins, than DDR4 and UniDIMM likely won't work.
It seems you are right...unidimm supports DDR3 & DDR4 chips but the socket has 260-pins.
 

ohsnaphappy

macrumors regular
Original poster
Jan 14, 2013
238
64
As a pro I want the fastest ram money can buy. As far as I know ddr4 will NOT work in the Skylake iMac. Meaning CL11 ddr3 2133mhz if the fastest money can buy.

If someone beats me to authentic test results with 2133 I would really appreciate it. If not, then I'll let you know my own results when the iMac arrives.
 

xgman

macrumors 603
Aug 6, 2007
5,052
838
I agree to get the fastest memory that will be stable in this new mac, but as seen on the current macs, there was very very little performance difference achieved by stepping up from 1600 to 1867 speed ram as I recall. Point is make sure you have stability first and speed second. Please let us know your results if it works at the rated speed. Not sure how you would test this without 1867 ram to compare a test with.
 
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ohsnaphappy

macrumors regular
Original poster
Jan 14, 2013
238
64
I agree to get the fastest memory that will be stable in this new mac, but as seen on the current macs, there was very very little performance difference achieved by stepping up from 1600 to 1867 speed ram as I recall. Point is make sure you have stability first and speed second. Please let us know your results if it works at the rated speed. Not sure how you would test this without 1867 ram to compare a test with.
If I buy it and post-production is stable I'll be happy. Even if the performance gain is purely psychological haha. I just want to make sure it's running at 2133, and not just saying 2133 in the system profile. I guess geekbench will tell me?
 
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