How does a SODIMM adaptor work?

[AshleyAshes]

http://www.ebay.ca/itm/1pc-DDR3-Laptop-SO-DIMM-to-Desktop-DIMM-Memory-RAM-Connector-Adapter-DDR3-New-DG-/172044891098?hash=item280eacb3da:g:434AAOSwJcZWgp5u

 

So, I have a combination HTPC/Server in my bedroom and I eventually want to separate it into two different builds, one dedicated HTPC and one server.  This means I need some extra parts, I have a spare mobo but need RAM and a CPU for it.  On a whim I asked myself 'I wonder if there's some kinda adaptor to use that 8GB of SODIMM DDR3 I have in a drawer in a desktop?'  So I go to Google and BAM, there it is.  ...So here's my question, if a SODIMM memory module has less pins than a desktop memory module, how on earth does this work?  It can't strictly be a simple pinout adaptor if it doesn't have the same number of pins?  But for five bucks there can't be much of ANYTHING on that aside from some dumb electrical pathways.  I also guess it makes sense, even if CPUs and memory have different mountings, DDR3 is DDR3 and Sandy Bridge is Sandy Bridge, so it should work out mostly electrically?  I just don't quite understand the mechanism at play here.

[thekeemo]

From the traces it looks like it is just a simple pinout adapter

edit nvm look at the 3rd pic

[Guest]

They don't.

[flibberdipper]

lmao that's not even a DDR3-style desktop connector. Looks a LOT more like regular DDR lmao lmaoooooo

[AshleyAshes]

2 minutes ago, tmcclelland455 said:

lmao that's not even a DDR3-style desktop connector. Looks a LOT more like regular DDR lmao lmaoooooo

What are you talking about?  It's absolutely a DDR3 connector, it even has the right number of pins.  Even from a glance you can tell, because the key notch on DDR3 is a bit farther off from center than it is on DDR1, 2 and 4.  

[Ben_Upde]

*edited*

incorrect information accidentally posted has been removed. 

[AshleyAshes]

Just now, Ben_Upde said:

SODIMMs have the same amount of pins, they are just considerably smaller to fit into a smaller form factor. This adapter just reroutes the contacts for full size DIMM connection. 

...DDR3 laptop memory has 204 pins where as DDR desktop memory has 240 pins...

 

How is this thread garnering responses from people who appear to have never even LOOKED at DDR3 memory before?

[Ben_Upde]

42 minutes ago, AshleyAshes said:

...DDR3 laptop memory has 204 pins where as DDR desktop memory has 240 pins...

 

How is this thread garnering responses from people who appear to have never even LOOKED at DDR3 memory before?

Ever heard of a little thing called dyslexia? 204 and 240 can look exactly the same to some people, especially when they are quickly browsing for information and not concentrating on every minute detail. 

Having said that you are correct. Even with tiny pins there are less of them. No need to be an a$$ about it. 

[Mark77]

The SODIMM standard, IIRC, drops the ECC/parity capability (ie: 72 bits vs. 64-bits), a feature that is provided on the "full sized" version of the standard.  And may even impose a limitation on the size of RAM modules ultimately allowed by reducing pins for address lines. 

 

Once you drop those 8 data lines (which may be differential pairs anyways!), and the associated power/ground lines for that 9th chip, voila, the pin count is reduced accordingly!  The adapter is constructed accordingly.

 

BTW, no need for anyone to treat anyone poorly.  Ashley's question is a very good one.

[AshleyAshes]

4 hours ago, Mark77 said:

The SODIMM standard, IIRC, drops the ECC/parity capability (ie: 72 bits vs. 64-bits), a feature that is provided on the "full sized" version of the standard.  And may even impose a limitation on the size of RAM modules ultimately allowed by reducing pins for address lines. 

 

Once you drop those 8 data lines (which may be differential pairs anyways!), and the associated power/ground lines for that 9th chip, voila, the pin count is reduced accordingly!  The adapter is constructed accordingly.

 

BTW, no need for anyone to treat anyone poorly.  Ashley's question is a very good one.

I've been comparing the pins and you're kinda right. the ECC pins are missing. There's also a number of redundant voltage pins that SODIMMs omit.  I actually ordered a pair of these adaptors when I first posted this thread but still awaiting the free shipping from China to deliver them and I'll report my results.  However I think there is promise.  there are ITX motherboards with desktop CPUs in them but also SODIMM slots and there are also mobile CPUs installed in desktop boards that feature full sized DIMM slots, so I see promise here if we're SODIMM is just cutting down on ECC and redundant pins.  Heck, a bunch of the pins on a DIMM are just 'NC' or 'No Connection' and serve no purpose what so ever.  18 NC pins on a DIMM vs 6 NC pins on a SODIMM.  All the data pins seem to be the same, 64 pins on either.

[Mark77]

Yeah I'm thinking the only real 'issue' you might see with the adaptors is reduced overclockability as the extra in-line capacitances and extra trace lengths will eat into margins.  Might be some minor other stuff relating to RF certification compliance as well (something that engineers have to worry about when they're designing equipment that has to undergo regulatory approval!).

 

Neither really apply to you, eh?  Actually most "homebuilt" PCs are technically out of compliance (ie: illegal) these days for lack of regulatory certification (CSA/UL, Industry Canada, etc.), but such is of practically no consequence to anyone. 

[AshleyAshes]

1 hour ago, Mark77 said:

Yeah I'm thinking the only real 'issue' you might see with the adaptors is reduced overclockability as the extra in-line capacitances and extra trace lengths will eat into margins.  Might be some minor other stuff relating to RF certification compliance as well (something that engineers have to worry about when they're designing equipment that has to undergo regulatory approval!).

 

Neither really apply to you, eh?  Actually most "homebuilt" PCs are technically out of compliance (ie: illegal) these days for lack of regulatory certification (CSA/UL, Industry Canada, etc.), but such is of practically no consequence to anyone. 

I think the biggest advantage is cost.  I have 2x4GB of SODIMM ram in a drawer, left over from a laptop upgrade, I can then use RAM in a build for about $14 in components as opposed to buying 8GB of RAM for around $50 or more.  It saves money and also puts perfectly good RAM to use.  Well, theoretically.   But yeah, I think it'll work, I just think I found a situation that few have considered as a way even possibly being an option.