Sidebar Sidebar
Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.

RAM Question

sdv5 said:
Skylake processors support DDR4 memory. Did Apple go out of their way to put in a crippled motherboard that would prevent DDR4 memory from working properly? That would seem too much trouble. Perhaps OP should investigate if DDR4 memory would work in the latest 27 retina iMac?
Click to expand...

Skylake's U and Y variants support one DIMM slot per channel, while H and S variants support two DIMM slots per channel.[19] Skylake's launch and sales lifespan occur at the same time as the ongoing SDRAM market transition, with DDR3 SDRAM memory gradually being replaced by DDR4 memory. Rather than working exclusively with DDR4, the Skylake microarchitecture remains backward compatible by interoperating with both types of memory. Accompanying the microarchitecture's support for both memory standards, a new SO-DIMM type capable of carrying either DDR3 or DDR4 memory chips, called UniDIMM, was also announced.
Click to expand...

Skylake supports both. Unless Apple put UniDIMM sockets in there, which seems VERY unlikely, we're gonna be stuck with DDR3 since the sockets are different for DDR3 and DDR4.
 
  • Like
Reactions: illitrate23
Further reading:

The UniDIMM specification was created to ease the market transition from DDR3 to DDR4 SDRAM. In previous RAM standard transitions, as it was the case when DDR2 was phased out in favor of DDR3, having an emerging RAM standard as a new product line created a "chicken or the egg" problem because its manufacturing is initially more expensive, yields low demand, and results in low production rates. The DDR2 to DDR3 transition issues were sometimes handled with specific motherboards that provided separate slots for DDR2 and DDR3 modules, out of which only one kind could be used.[8] By its design, the UniDIMM specification allows either DDR3 or DDR4 memory to be used in the same memory module slots, resulting in no wasted motherboard space that would otherwise be occupied by unused slots.
Click to expand...
 
  • Like
Reactions: illitrate23
syndr0me said:
Skylake supports both. Unless Apple put UniDIMM sockets in there, which seems VERY unlikely, we're gonna be stuck with DDR3 since the sockets are different for DDR3 and DDR4.
Click to expand...
Thanks for the info. But a single stick of DDR3 memory is limited to 8GB whereas DDR4 can contain up to 16GB in a single stick. How then is OWC able to offer 64GB RAM upgrade for the latest iMac starting tomorrow?
 
sdv5 said:
Thanks for the info. But a single stick of DDR3 memory is limited to 8GB whereas DDR4 can contain up to 16GB in a single stick. How then is OWC able to offer 64GB RAM upgrade for the latest iMac starting tomorrow?
Click to expand...
Scratch that, just found that Crucial offers a 16GB single stick DDR3 for a lot less money than OWC.
 
  • Like
Reactions: Cisco_Kid
OWC appears to be greatly overpriced.

As far as the 16GB sticks go, I'm not an expert, but I don't think there's a 8GB limit on DDR3 sticks.
 
  • Like
Reactions: Cisco_Kid
  • Like
Reactions: skodacars
Ugh so my company gives us a scheme where we can buy Apple products, interest free over 2 years and it has some tax benefits....

I ordered the previous iMac 5K specced up to 4.0ghz i7, 295X 4GB, 1TB Flash Storage, 8GB Ram and got a e-mail from them today saying they are cancelling that order (as it never actually went through) and changing it to the NEW one, 27" 5K, 4.0ghz i7, 395X 4GB Graphics, 1TB Flash, 8GB RAM

BUT in my excitement i bought 32GB of Crucial for the previous mac model, DDR3 1600 in x4 8GB Sticks.

Question is; if i take out the x2 4 1866mhz and populate the mac with the x4 8GB 1600 sticks i bought a few weeks ago, will it have any detrimental impact on the speed / will it even boot? I remember older mac's were funny with what speed sticks you put in, you had to have at least 1 which matched the stock spec.

Thanks!
 
Lucky you :D
And the machine will boot, you will just have lower RAM performance (bandwidth and speed), not noticeable in the real life ;)
 
Crucial off Amazon is cheaper than the OWC for me (being in Canada with the exchange), is there any performance difference? Should I go with Crucial?

Kingston HyperX Impact is much more expensive so I sort of ruled that one out.
Any thoughts?
 
  • Like
Reactions: Textureboy
Excellent thread here. I am in the same position.... Which brand is best
Here is what I have found from Amazon.CA
Can someone tell me that both of these are absolutely compatible.

Crucial Ballistix Sport SODIMM 16GB Kit 8GBx2 DDR3 1866 MT/s PC3-14900 CL10 at 1.35V 204-Pin Memory BLS2K8G3N18AES4

And

Kingston Impact SODIMM - 16GB Kit* (2x8GB) - DDR3L 1866MHz CL11 SODIMM - 16 GB (2 x 8 GB) - DDR3L SDRAM - 1866 MHz - 1.35 V - Unbuffered - SoDIMM

Thanks guys!
 
sdv5 said:
Thanks for the info. But a single stick of DDR3 memory is limited to 8GB whereas DDR4 can contain up to 16GB in a single stick. How then is OWC able to offer 64GB RAM upgrade for the latest iMac starting tomorrow?
Click to expand...
sdv5 said:
Thanks for the info. But a single stick of DDR3 memory is limited to 8GB whereas DDR4 can contain up to 16GB in a single stick. How then is OWC able to offer 64GB RAM upgrade for the latest iMac starting tomorrow?
Click to expand...

Not too sure where you get that from or indeed why the big hang up over DDR4 over DDR3.

In theoretical terms DDR3 is limited to 128gb per stick and DDR4 is limited to 512gb per stick.

Now I've never seen any DDR3 module bigger than 16gb but that doesn't mean it can't be manufactured subject to the necessary chipset/cpu support.

Even so a total of 16gb is fine for the majority of users, 32gb is overkill and on current availability/support it appears that we can easily double the overkill.

Would anyone who is considering an iMac even get near seriously needing 64gb in RAM in the next few years?

If they need more then I would respectfully suggest that they would not be looking at an iMac.

It's similar with transfer speeds. If you take the fastest possible DDR3 it does indeed have a data transfer half that of the fastest possible DDR4.

That said, the DDR3 in the iMac is not the fastest possible and i've not yet seen DDR4 running at the highest possible speed out in the wild in serious quantities yet.

IMO the main reason for DDR4 to gain serious traction in the market so far is that there is a serious cost penalty in using it and only marginal technical benefits at this time.

In fact it reminds me of the old comparison between SATA1 and PATA133. The faster, newer method maxed out at 150Mb/s, while the older system was running at 133Mb/s

Other than an easier cable configuration that promoted better airflow there weren't too many that signed on to a system that promised a peak transfer rate 10% greater than the current best and even then that wasn't the bottleneck.

Most HDDs were physically incapable of exceeding 100Mb/s at that time.

Obviously technology moved on and once SATA2 with it's 300Mb/s peak transfer rate was available and drive technology improved people got onboard.

I'm sure that DDR4 will slowly gain acceptance, but for me it's too much of a price hike for not enough performance.
 
I think it's impossible to anticipate everybody's use case when it comes to RAM. I have to stand up quite a few virtual machines to develop the current project I'm working on, each of which requires at least 2GB or processes get OOM-killed. That's probably gonna grow to 3GB each soon. That's in addition to the RAM the OS uses. Some scenarios are more RAM intensive than others.

That said, I agree that 16GB is probably more than enough for most people, and will likely be enough for many years to come.
 
Anyone shed some light on memory timings? Is there any real difference between cl 11 or 10 or 9? Sometimes the slightly lower speed ram is cheaper. Does it matter?
 
I ordered 16 additional gigs for 24 total.

I will be doing intensive Photoshop, Zbrush, Maya, Logic and Reason, plus standards like Safari and iTunes. 24 should be fine right?
 
I know in the past some people have had issues mixing other brands of RAM with what ships in the iMac. Random crashes and such. I'm planning to order 32GB from Crucial once it's been 100% verified what works, and then selling the pre-installed stuff on eBay, or possibly someone on here if this forum has a buy/sell/trade thing going on.
 
Does anybody know what is the CAS latency of the stock ram (from Apple) that ships with the iMac?

OWC has ram that they say is compatible with the new iMac and it is CL11. Does this mean the Apple stock ram is also CL11?

The reason I ask is because I ordered the iMac with 8GB of ram and am only interested in buying a set of ram (2 modules) to fill the 2 empty slots.

Are there any negative effects of mixing two sets of ram where the only difference between them is their CAS latencies? For example, let's say that the stock ram from Apple is CL11 and I buy a set of CL10 ram to fill the 2 empty slots. Will the ram function properly after installed? Will I need to make modifications through some kind of software to make them work together? Or is this just a bad idea?

I am on the fence about buying CL10 (Crucial) or CL11 (OWC) since I don't know which of these CL's (if either) ships with the iMac. If these differences do not matter, Crucual is more affordable, and from what I have read, it might be ever-so-slightly faster due to lower latency. So, if I could get the CL10 from Crucial, I'd be happy.
 
  • Like
Reactions: zerae
Jasons0147 said:
Just to confirm, this is the same ram you mentioned and would work on the 27' iMac i just ordered? Also when I install it do I just put them in the 2 empty slots or do I need to change the order?

http://www.amazon.com/Crucial-Balli...63&sr=8-2&keywords=Crucial+Ballistix+1866+MHz
Click to expand...

Northcoast said:
Excellent thread here. I am in the same position.... Which brand is best
Here is what I have found from Amazon.CA
Can someone tell me that both of these are absolutely compatible.

Crucial Ballistix Sport SODIMM 16GB Kit 8GBx2 DDR3 1866 MT/s PC3-14900 CL10 at 1.35V 204-Pin Memory BLS2K8G3N18AES4

And

Kingston Impact SODIMM - 16GB Kit* (2x8GB) - DDR3L 1866MHz CL11 SODIMM - 16 GB (2 x 8 GB) - DDR3L SDRAM - 1866 MHz - 1.35 V - Unbuffered - SoDIMM

Thanks guys!
Click to expand...

I havent seen a link to 16gb (2x8gb) of ram that I could purchase off Amazon, is it possible that someone could link one? Im in the US and I would like to buy something that is Prime eligble.

Just to clarify I have obviously seen several different Ram options on Amazon but I could not find a way to verify that it would work in the new 27' IMac.
 
As an Amazon Associate, MacRumors earns a commission from qualifying purchases made through links in this post.
syndr0me said:
I know in the past some people have had issues mixing other brands of RAM with what ships in the iMac. Random crashes and such. I'm planning to order 32GB from Crucial once it's been 100% verified what works, and then selling the pre-installed stuff on eBay, or possibly someone on here if this forum has a buy/sell/trade thing going on.
Click to expand...
Apple iMacs are not made from dragon scales... The memory controller is in the Intel CPU, if you don't mix modules, you can even put 2133 MHz So-DIMM, and it will work fine.
Apple sold 1600MHz memory in my late 2013 iMac, but the Crucial Ballistix 1867 MHz work perfectly in it: my i7 supports this speed. And would support 2133MHz modules too ;)
 
You must log in or register to reply here.
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.
Top Bottom
Back