memory compatibility

[Doug Lassiter]

Probably a silly question, but how intercompatable are memory cards in Macs?

For example, I have a 2011 MacBookPro 8,1 that I'm going to do a memory upgrade on. So I'll be pulling out a couple of 1333MHz DDR3 204 pin SO-DIMMs and replacing them.

Now, I have a late 2009 iMac 10,1 that has a couple of extra slots. That machine normally takes 1066MHz DDR3 204 pin SDRAMs.

Could I put those replaced SO-DIMMs from the MBP into the iMac and expect them to work? Same number of pins. If the architecture is the same, but the SO-DIMMs are just faster then perhaps they are downward compatible?

Is there some writeup somewhere about what is compatible with what, or is the deal simply that nothing is intercompatible? Would appreciate guidance by someone with some real chip savvy.

 

[Raz0rEdge]

Beyond just the speed, there are other things like refresh timing and so on. Generally, you can use faster RAM on a machine that works with slower RAM since the RAM can be accessed at the slower rate. But if there is a refresh timing mismatch, then you're going to have issues with memory corruption.

For best (and ideal) performance, it is always good to use RAM that is meant for a machine machine across all aspects (bus speed, refresh timings, etc).

 

[Doug Lassiter]

Thank you. But what I read is that refresh timing is a matter of device generation, as in DDR number. These are all DDR3 chips. That being the case, the matching should be assured. You'd think there is some published wisdom about this.

 

[pm-r]

Is there some writeup somewhere about what is compatible with what, or is the deal simply that nothing is intercompatible? Would appreciate guidance by someone with some real chip savvy.

There's probably lots of info out there and our local CanadaRAM.com is our local excellent memory expert, but I'm sure the faster chip is backward compatible in your older iMac but it will probably just run at the same speed as the original chips.

Checkout:
https://discussions.apple.com/thread/3333325

or google the 'net.

Anyway, at least it's easy to remove if it doesn't work and it won't do any damage trying. I'd say go for it.

Also see:
https://apple.stackexchange.com/questions/48607/will-early-2009-imac-accept-faster-than-spec-ram







- Patrick
======

 

[Doug Lassiter]

That's helpful. Those links speak directly to my question. So people say yes, it can work. Though at least one says it didn't. A little odd that people in the apple.com discussion are suggesting that 1333MHz memory in your 1066MHz system should make your system run faster ... duh? No question that the bus speed is determined by the computer, and not by the RAM. The RAM just has to be able to handle the bus speed.

I think it's also significant that, at the least, the things are plug-compatible. I mean, if it didn't fit, it couldn't work!

Now, I did try googling the net, but found nothing. Maybe you're a better googler?

I have to add that really, I can't imagine Crucial or OWC telling you you can do this. They want to sell memory!

 

[Raz0rEdge]

Thank you. But what I read is that refresh timing is a matter of device generation, as in DDR number. These are all DDR3 chips. That being the case, the matching should be assured. You'd think there is some published wisdom about this.

No DDR3 is the 3rd generation of the DDR type RAM. It has nothing to do with refresh timings. You cannot use DDR3 memory on a system that doesn't support DDR3, that won't work at all.

But if a system supports DDR3 and you have DDR3 memory, if there is a slight speed mismatch, that shouldn't be a big issue.

 

[Doug Lassiter]

No one is talking about using DDR3 memory on a system that doesn't support DDR3. In fact, now that I research more closely, even within DDR3 devices, there can be large differences in refresh timing across different device sizes. So refresh timing isn't even an issue, since you can use many different device sizes in the Mac slots. So that's true that DDR number is evidently not particularly relevant to refresh timing.

https://ieeexplore.ieee.org/document/7070756/

 

[pm-r]

I have to add that really, I can't imagine Crucial or OWC telling you you can do this. They want to sell memory!

Actually, often if you ordered the faster RAM several years ago from most good RAM dealers, you would often receive the faster backward compatible chip modules as they were usually cheaper and the older chips were out of production. I would imagine that the situation is still similar if not more so.

I have had such modules working in some of our Macs for years now, and they works just fine. Even when installed as mixed speeds.

BTW: Using this 2009 iMac as a typical example you can see where it says:
RAM Type: PC3-8500 DDR3 Min. RAM Speed: 1066 MHz
Details: Supports 1066 MHz PC3-8500 DDR3 SO-DIMMs (204-pin).


Notice it says: Min. RAM Speed: 1066 MHz

I'd say you're good to go and I'd be very surprised if those 1333MHz 204 pin RAM modules didn't work in your 2009 iMac.

And good thinking BTW, to install and utilize the removed modules.








- Patrick
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[Doug Lassiter]

Yes, while I can get a rebate on replaced modules, that rebate is insultingly low. Just a few bucks. They probably turn them around and sell them at an enormous profit. I'll put in my order for new RAM for my MBP, and I should get it ina week or so. I'll upgrade my MBP with them, and then take the old 1333GHz RAM and stuff it in one of my 1066GHz iMacs. Will let you know how it goes. Thank you to everyone. This has been an illuminating discussion.

 

[Doug Lassiter]

OK, just reporting back. Using two 2GB 1333 GHz DDR3 RAM cards (from a MacBook Pro 8,1) in an iMac 10,1 (for which 1067MHz DDR3 cards are native) DOES work. Appears to be just fine. I have yet to run the Extended Hardware Test, however. Will report back if it fails that. Interestingly, the iMac System Report lists these RAM cards as being 1067MHz. Evidently, it doesn't check. It just assumes that's what they are. The "About This Mac" page is a little more careful. It says "Your Mac contains 4 memory slots, each of which accepts a 1067MHz DDR3 memory module." That's true, it "accepts" those. But it appears that it also accepts the faster cards.

Bottom line. When you upgrade memory on a Mac and have extra cards left over, might think about whether those cards can be used on another machine, instead of getting a paltry rebate for them. Looks to me that 1333Ghz cards are downward compatible to 1067MHz systems.

 

[pigoo3]

Thanks for the update. Good information.

- Nick

 

[Raz0rEdge]

OK, just reporting back. Using two 2GB 1333 GHz DDR3 RAM cards (from a MacBook Pro 8,1) in an iMac 10,1 (for which 1067MHz DDR3 cards are native) DOES work. Appears to be just fine. I have yet to run the Extended Hardware Test, however. Will report back if it fails that. Interestingly, the iMac System Report lists these RAM cards as being 1067MHz. Evidently, it doesn't check. It just assumes that's what they are. The "About This Mac" page is a little more careful. It says "Your Mac contains 4 memory slots, each of which accepts a 1067MHz DDR3 memory module." That's true, it "accepts" those. But it appears that it also accepts the faster cards.

Bottom line. When you upgrade memory on a Mac and have extra cards left over, might think about whether those cards can be used on another machine, instead of getting a paltry rebate for them. Looks to me that 1333Ghz cards are downward compatible to 1067MHz systems.

Thanks for validating what I said in post #2.

 

[pm-r]

Looks to me that 1333Ghz cards are downward compatible to 1067MHz systems.

Thanks for validating what I said in post #2.

Ditto, but for my posts #4 and #8.

PS: Your Mac is reporting the slower speed as that is the maximum speed the "faster" modules can run in that Mac model.

PPS: All our Macs are using "hand-me-down" memory modules that luckily were compatible. Unfortunately some old memory modules just become interesting techy keychains for the grandkids.




- Patrick
======

 

[Doug Lassiter]

So I did a RAM integrity test on the iMac with some 1333GHz RAM installed (instead of just 1067MHz RAM) using MemTest86. Passed with flying colors. Boy, MemTest sure works it hard. Can almost see the beads of sweat on my RAM!

Interestingly, MemTest reports in "RAM Info" that these are 1067GHz cards. So I have to assume that the cards can't actually get polled to see their speed, but just that everyone has to assume that what is there is what is supposed to be there. I would have used the Apple Hardware Test, but that seems not to be resident on my iMac.

Yes, it's nice that cards can be "luckily compatible". Would be even nicer if someone could just say that, so it isn't a matter of luck. Of course, OWC and Crucial would never want to tell you that.

 

[Raz0rEdge]

Your iMac has a 1067 MHz memory bus, you can put ANY faster memory in there and EVERY application will report it as a maximum of 1067 MHz since that's what the hardware is.

 

[Doug Lassiter]

Your iMac has a 1067 MHz memory bus, you can put ANY faster memory in there and EVERY application will report it as a maximum of 1067 MHz since that's what the hardware is.

Well, the hardware was a 1333MHz RAM card, not a 1067 MHz RAM card. So that hardware wasn't telling the machine what it's speed was. If I put on a small shirt, even though my size is large, you don't get to tell me that I'm wearing a large-sized shirt. You can close your eyes and presume that, though.

 

[Raz0rEdge]

The hardware here is the memory bus of the iMac, not the RAM. Anyway, you've proven that the RAM is working, leave it at that.

 

[pm-r]

If I put on a small shirt, even though my size is large, you don't get to tell me that I'm wearing a large-sized shirt. You can close your eyes and presume that, though.

Hmmm… that probably depends on if you're a female or not and on the size of your breasts!!!

And yes, I can close my eyes and visualize certain situations relating to large-sized shirts and some resulting body visual effects.




- Patrick
======

 

[ferrarr]

Well, the hardware was a 1333MHz RAM card, not a 1067 MHz RAM card. So that hardware wasn't telling the machine what it's speed was. If I put on a small shirt, even though my size is large, you don't get to tell me that I'm wearing a large-sized shirt. You can close your eyes and presume that, though.

I think you have that backwards, since the ram you used was faster (larger) than what you needed. You would have to put on an extra large shirt, to get the same affect.