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Compatibility with different types of memory[edit]

There is a new version, ddr2 sodimm. I bought it for a ddr sodimm laptop and it is incompatible. Maybe some information should be added. (-someone)

Agreed. There should be info on what type of memory is supported. I.E: a 266mhz is backward compatible with 133mhz but other are not... is that the case?

DDR or DDR2 are not backward compatible with other kinds. PC133 is not compatible with Intel 440xx and 810 chipset using PC100. (-someone)

Usually the situation is more complex. Usually within a type, the faster modules are SOMETIMES backwards compatible. Often the problem is with "chip density" -- when the module is faster AND built with denser chips, maybe for greater total capacity, then it may not work in older slots designed earlier. 21:41, 26 November 2006 (UTC)

We are no longer in the days of non-DDR SDRAM[edit]

Why does it talk about "regular" 168-pin RAM? Nowadays the norm is 184- or 240-pin memory. Geekosaurus


I demand information on DDR and DDR2 SODIMMs!-- 21:00, 7 October 2006 (UTC)

At Nov. 27, 2006 my friend and I were attempting to use the SO-DIMM wikipedia page to verify the type of ram he had purchased. The labelling of the ram he had purchased, the labelling of the ram he had installed, and the wikipedia page did not correspond. After some research, I have determined that the key notch for DDR2 belongs towards the center of the ram board, while DDR goes towards the outside. For reference, see Jedec document section 4.20.6 for SO-DIMM DDR voltage specs, Jedec document section 4.20.11 for DDR2 voltage specs, and Jedec document MO-224 for schematic layouts of the physical boards. Note that as per Jedec section 4.20.6, that DDR is 2.5-2.7V, with the left key (outwards) used and right key reserved. Jedec section 4.20.11 has DDR2 at 1.8V, with the right (inwards) key used and the left key reserved. Document MO-224 does not reference common names (DDR vs. DDR2), but does confirm the position based on voltage. I have corrected the page as such, and hopefully someone more knowelegable can verify. Macavity 01:02, 28 November 2006 (UTC)


We need pictures of each type, with a ruler and at the same scale, so people see the notches etc. 21:37, 26 November 2006 (UTC)


The different types of SO-DIMMs can be recognized at a glance by the distinctive notches used to "key" them for different applications: 100-pin SO-DIMMs have two notches, 144-pin SO-DIMMs have a single notch near (but not at) the center, and 200-pin SO-DIMMs have a single notch nearer to one side.

This is to a degree incorrect, I have a 16mb RAM stick in a Digital Hi-Note VP and a 64mb stick in a Toshiba Tecra 8000, the sticks ARE NOT compatable even though they both have 1 notch, they are about 1mm from aligning with each other. It is a possiblity that Digital used propriatry RAM but I have no idea as the laptop is probbably older than I am, and it was given to me freely without any manual etc :(

DDR and DDR2 pictures - notches[edit]

As of 11/19, regarding the two pictures used to illustrate the distinguishing different notch locations for DDR and DDR2 memory. The article says the notch is closer to the center for the DDR2 memory. In the pictures don't the notches appear to be in the same location relative to the sides of the memory? If the DDR2 memory picture really is of DDR2 memory then there actually isn't much difference in notch location.

Gloryroad (talk) 17:08, 18 November 2007 (UTC)

I cropped and resized the existing photos of DDR and DDR2 and compared them closely, edge to edge. There is a very-very-very small difference between the two notch locations, much less then I'ld have expected in my ignorance of DDR2. Plus the DDR2 seems to have 19 contacts, versus DDR's 20, on the short side of the notch. One wonders why the designer(s) would bother changing the notch location, seemingly to distinguish the two, and then not make the difference large enough to be immediately apparent. If 19 contacts to the side of the notch is consistent with DDR2, perhaps that is a better indicator.

If this is all correct, it might be helpful if the article emphasized that the notch difference is minute (not just slight) and requires careful observation to distinguish.

Gloryroad (talk) 14:05, 22 November 2007 (UTC)

(Deleted stupid guy's irrelevant mumbling in French. Please feel free to take this whole thing out altogether) Ngtt (talk) 21:51, 6 August 2008 (UTC)

I note that the DDR picture has been removed since these comments were added. It would be useful for those of us attempting to distinguish the two types if it (or an equivalent) could be returned. I'm not sure why it was removed, but I'd say it's definitely an informative addition to the article. JulesH (talk) 17:25, 8 September 2009 (UTC)

Hi, I came across this wiki page because I wanted to know how to visually distinguish between DDR and DDR2 memory types. From the discussion on the main article it seems as though to make an accurate identification of a single DDR or DDR2 module (without having 2 side by side for comparison) you need to get a ruler out and start measuring stuff. It's not really clear how one can tell if the notch is "further to the centre" or "further to the edge" unless you can make a visual comparison between 2 modules. I think a clearer explanation is to state that for a DDR2 module the notch is closer to the 21st pin than the 20th pin, while for a DDR module, the notch is closer to the 20th pin than the 21st pin. In this way you can identify the module type just by visual inspection. Chohr (talk) 22:13, 13 May 2011 (UTC)

To clarify what I mean, an image like this one: or this one: would be perfect. Here you can see that on the DDR2 module the notch is practically touching the 21st contact, while on the DDR1 module the notch is closer to the 20th contact, but isn't particularly close to either the 20th or 21st contact. Using this information you can quickly identify if a module is DDR1 or DDR2 by visual inspection alone. Anyway, in summary I think it's better to talk about the location of the notch relative to contacts 20 and 21, rather than relative to the edge/centre of the module. Chohr (talk) 22:46, 13 May 2011 (UTC)

DDR2 (5300) - Mac vs. PC versions[edit]

Is there any difference between DR2 5300 SO-DIMM that is recommended for Mac (mini), versus for any PC (based laptop)? —Preceding unsigned comment added by (talk) 02:38, 8 December 2008 (UTC)

Hmmm, should I remove?[edit]

"At the time of writing (May 2008) DDR2 SO-DIMM memory modules commonly have clock speeds from 200 MHz up to 800 MHz PC2-6400 and 1066 MHz PC2-8500 are becoming available." as stated at the bottom of the article is a year ago. I don't know the outdated template code, so I came here to discuss it instead. Any input?--Airplaneman (talk) 23:34, 21 May 2009 (UTC)

Generally speaking, per WP:V, if the assertion has no source, you may feel free to remove it, or consider tagging it {{citation needed}} as a courtesy to allow other editors a bit of time to find a source should they want to retain the claim in the article. Claims that remain should, over time, be cited with inline citations. N2e (talk) 21:34, 3 October 2009 (UTC)

Advice to readers trying to identify memory[edit]

From the standard-setting point of view, a minute difference in notch position (say, 0.3 mm) is enough to prevent insertion of a memory module in an incompatible motherboard. Notch position was not designed to facilitate module identification. Worse, the vendors do not always provide on the label the information you need to determine whether the module is compatible with your system.

Never try to insert a module with the wrong key. If it is not seated properly you could have a hundred short circuits and your motherboard will smoke.

The best way to determine what kind and how much memory your computer can use is to go to a vendor such as Kingston Technology or Crucial Technology and use the memory advisor link on their home page. This does not obligate you to buy from Kingston or Crucial.

Since there is so much confusion, and so many readers are trying to use Wikipedia to identify memory modules, perhaps we should mention this in the various articles on memory modules. Yes, I know it is not exactly "encyclopedic", being shopping advice. Solo Owl (talk) 04:04, 25 October 2009 (UTC)

Please add discussion of what the extra 36 pins on DIMM are for[edit]

I've seen claims in many online discussions that SO-DIMM performance is the same as DIMM. But there must be some benefit to having 36 extra pins -- otherwise, I'd think the DIMM format would have been abandoned. What purpose(s) do they serve?Therealdp (talk) 15:33, 4 January 2015 (UTC)

Hello! That's a very good question, and we should probably start by comparing the specs of a DDR3 DIMM and a DDR3 SO-DIMM (pinouts are on page 3 in both PDF files). The DDR3 DIMM pinout says that 30 pins (out of 240) are actually unused for single-rank DIMMs, while double-rank DIMMs leave 26 pins unused. That leaves us with only six (240 − 204 − 30) extra pins on DDR3 DIMMs. A closer examination reveals that DDR3 SO-DIMMs don't have DQS8, DQS8 and DM8 signals (what's three more pins), which are used only for ECC UDIMMs according to the page 7 in this spec.
All that leaves us with the room for a difference of three extra pins on DDR3 DIMMs. I hope that perhaps you could take it further and make the list of exact differences based on these two pinouts. :) — Dsimic (talk | contribs) 01:59, 5 January 2015 (UTC)