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I was browsing for a RAM upgrade earlier for my system, and came across 'AMD-only' RAM (aka, RAM that only works on AMD chipsets). This RAM can easily be found on sites such as eBay, and seems to be slightly cheaper than 'normal' RAM.

The RAM prompts a question: is this RAM really restricted to AMD chipsets?

When considering RAM for a system, there are certain considerations to make such as:

  • Speed (1066MHz, 1600MHz, etc);
  • CAS (latency, lower is better);
  • Generation (DDR2, DDR3, DDR4, etc)

However there is usually no such consideration as chipset compatibility. Sure, it's possible to guarantee that a given stick of memory will work if it's within the bounds of the chipsets listed in the information given by the seller/manufacturer.

For instance if a series of chipsets supported RAM between 1600MHz and 2400MHz, with 9-12 CAS, and on DDR3, it would be possible to list a product as being fully compatible with that series of chipsets if the said RAM was 2000MHz, 10 CAS, and DDR3.

I suspect that's partially the story here. However, is it possible at all for a given stick of memory to be 'AMD-only' or 'Intel-only', and if so, how?

  • Just study any IC's data sheet and you'll notice that there are many more important details, which are usually not mentioned (or else consumers would get even more frustrated than they are). Tolerance values for voltages, power consumption, signal edge steepness, 0/1 threshold levels etc are among the parameters which are usually standardised. I don't know the details in this case but could imagine that if AMD allows for higher tolerance values, this allows vendors to sell chips which they would usually have to destroy because they're slightly out of specification. – Run CMD Mar 3 '16 at 16:01
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    It is a "thing" in that AMD has one set of SPD extensions and intel has another, but as far as I know, they both should have the basic fallback to DDR2 jedec information. Possibly the reason they are marked AMD only is that they are presuming the end-user cannot manually set timings if the SPD info is not honored (major box vendors have poor manual BIOS configuration support). I won't make an answer though because I don't have good evidence for this. – Yorik Mar 3 '16 at 16:12
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    @Ramhound That's my point though, I suppose my actual question is 'is this just sellers trying to market the RAM modules, or is there another reason?'. – AStopher Mar 3 '16 at 16:18
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    I was wildly guessing, but if it's the case, then yes. Similar to how they introduced triple core processors -- the probability of one core being defective is high enough to consider not throwing that quad core away. But it may also be the case that the RAM was supposed to be faster or something, and that you cannot rely on its SPD or it was disabled. Which is basically a similar case -- a piece of silicon which does not fully meet its specification. – Run CMD Mar 3 '16 at 16:44
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    I don't know how it's possible, but it did bite me. My brother bought 2x4GB sticks of DDR2 memory, because he wanted to use it on gigabyte ga-g41m-es2l motherboard, which does support 8GB DDR2 RAM. And...it didn't work because he bought one for AMD and not for intel. It posts, the RAM is detected (all 8GB of it) and then it just reboots a few seconds later, sometimes with some visual glitches. We also tried to decrease the frequency and set worse timings in BIOS still on old RAM, and try again, but that didn't change anything, that seems to exclude it being slower. And it works on P31 chipset. – barteks2x Apr 14 '18 at 13:43
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+50

It is true that for the AM2 chipset (DDR2) and early on in the AM3 (DDR3) chipset era, AMD supported higher density RAM than Intel did. Intel started supporting the higher density RAM, but I can't find the exact chipset on which it was introduced.

Essentially AMD provided an additional physical address line per RAM page (11 vs. std 10) which doubles the amount of memory that can be addressed on a RAM stick, allowing their chipsets to use the high density RAM. For example, a DDR2 stick for an Intel chipset may have had 8 memory chips, each with a capacity of 128 MB, resulting in 1 GB stick. AMD, with the additional address bit, could use a stick with 4 256 MB chips, also with a total of 1 GB.

The net benefit for AMD users was a slightly lower cost per GB of RAM and a higher max capacity per chip as compared to Intel.

I would bet that this high density memory would have worked fine in an intel motherboard (all other parameters assumed to be compatible), but it would only see half the capacity.

The best write up I could find on this was buried at OCZ Technologies website and was only available from archive.org: http://web.archive.org/web/20100210134333/http://www.ocztechnology.com/products/memory/ocz_ddr2_pc2_5400_am2_special_high_density_kit-eol

With 11 column address bit support by the AM2 memory controller, the number of addresses in each row or page can be as high as 2048 individual entries for a page size of 16kbit. Unlike modules based on standard 10-bit column address chips with an "8k" page size, the new Titanium AM2 Special modules take advantage of the AM2 controller's feature set and provide a single rank solution with 2GB density using 16k pages. This allows the controller to stay in page twice as long compared to standard memory architectures, thereby achieving unparalleled performance.

That was a good question.

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What is happening in most of them is that they are based on x4 chips instead of the x8 chips normally used, which was never officially supported by JEDEC on unbuffered DIMMs and don't work on Intel.

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    @cybermonkey Why is this downvoted? AMD-only DDR2 RAM is usually 2Rx4 instead of 2Rx8. It has 16 chips on each side/rank for a total of 32 chips. While from experience and spec, Intel DDR2-era boards only supported 1Rx8/2Rx8/1Rx16 RAM (8/16/4 total chips respectively). – guest-vm Apr 6 '18 at 22:11
  • @guest Probably because it doesn't add anything new to the Q&A. – AStopher Apr 7 '18 at 8:45

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