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Computer Memory DDR3, Difference Between UDIMM & DIMM

09/12/2015 1:03 PM

Hi fellow engineers, this may sound a bit of a teaser, but I need to upgrade my desktop computer RAM and I can't find what the difference between the manufacturer's recommended type UDIMM and the standard desktop 240 pin memory stick just called DIMM.

Obviously SODIMM has only 204 pins and is a different physical size.

I've checked manufacturers data and the DIMM and UDIMM modules have the same data sheet!!

Does anyone know if there is a difference is it important??

This is important because most DDR3 modules are just DIMM and they are cheaper than the UDIMM's

The complete spec I need is DDR3 PC3-12800 (1600) 240 pin

John.

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#1

Re: Computer memory DDR3, difference between UDIMM & DIMM

09/12/2015 1:28 PM

"Inside of the DIMM form factor are several different but closely related electrical and logical interfaces.First is the unbuffered DIMM, or UDIMM. Unbuffered DIMMs expose all signals from the SDRAM ICs (the memory chips) to the IO bus. There is no intermediary."

http://www.tomshardware.com/answers/id-1893807/difference-udimm-dimm.html

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#2
In reply to #1

Re: Computer memory DDR3, difference between UDIMM & DIMM

09/12/2015 1:38 PM

Yes, interesting SolarEagle but it still doesn't answer my question of what is the difference....

OK so a couple of replies state that their is little or no difference, but is it the same in practice??

Because my desktop's manufacturer (Lenovo) states to use their range of UDIMM's, is this just a marketing ploy or is there any significant difference?

John.

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#3
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Re: Computer memory DDR3, difference between UDIMM & DIMM

09/12/2015 2:03 PM

"DIMM tells us a lot about the mechanical and electrical properties of of the device and when coupled with a particular generation of memory provides for mechanical compatibility.

Any DDR3 DIMM can be inserted into any DDR3 DIMM slot.

Derivative forms such as SO-DIMM, MicroDIMM, and UniDIMM may contain the exact same chips but are mechanically incompatible.

Inside of the DIMM form factor are several different but closely related electrical and logical interfaces.

First is the unbuffered DIMM, or UDIMM. Unbuffered DIMMs expose all signals from the SDRAM ICs (the memory chips) to the IO bus. There is no intermediary.

Next is the registered DIMM, or RDIMM. Registered DIMMs buffer the command and clock signals as these experience a much greater electrical load than the address and data signals. This allows more memory ranks to be connected to the same bus. RDIMMs are used in most servers and workstations.

Next is the load-reduced DIMM, or LRDIMM. Load Reduced DIMMs buffer everything in both directions (upstream and downstream from the memory controller). LRDIMMs are used in extremely high end servers with massive amounts of memory.

Both RDIMMs and LRDIMMs contain additional onboard circuitry to buffer the signals whereas UDIMMs do not.
UDIMMs, RDIMMs, and LRDIMMs all have the same pinout and are mechanically compatible.

While consumer platforms typically only accept UDIMMs and only high end servers accept LRDIMMs they are mechanically compatible. It is possible to insert a DDR3-LRDIMM into any DDR3-DIMM slot, but there's a good chance that the firmware will simply refuse to initialize it and thus refuse to boot. Servers and workstations on the other hand can use either UDIMMs, RDIMMs, or LRDIMMs (if supported)."

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#4
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Re: Computer memory DDR3, difference between UDIMM & DIMM

09/12/2015 2:48 PM

I think they key here is "is it supported?", by the mfgs CPU etc. There's recommended and then there's supported.

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#5
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Re: Computer memory DDR3, difference between UDIMM & DIMM

09/12/2015 3:27 PM
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#6
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Re: Computer memory DDR3, difference between UDIMM & DIMM

09/12/2015 3:46 PM

Oh well, that's put the cat amongst the pigeons....

In those links it says my Thinkcentre M58p takes both SO-DIMM or UDIMM.

When I put in the exact model number it says it only supports UDIMM, as Lenovo sells both UDIMM, DIMM and SO-DIMM and when I select compatible memory it only shows me UDIMM, its basically saying don't use DIMM I guess.

But now the first link says M58p supports both SO-DIMM and UDIMM which is physically impossible

I think the next step is to take out the DIMM already installed, count the pins and photograph it, to find out what it is using

Thanks anyway folks, if anyone else can offer some advice please chip in.

John.

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#7
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Re: Computer memory DDR3, difference between UDIMM & DIMM

09/12/2015 6:00 PM

Well one model is the Eco ultra small FF (sodimm 4g)and one is the tower(udimm 8g), both M58p....

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#12
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Re: Computer memory DDR3, difference between UDIMM & DIMM

09/14/2015 2:06 AM
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#8

Re: Computer Memory DDR3, Difference Between UDIMM & DIMM

09/12/2015 6:16 PM

I have used the Crucial website to determine the interoperability of RAM. They have a free piece of code that you download into your machine and in a few seconds it tells you which of their products (RAM, SSDs, etc.) are compatible with your machine.

You will get their entire list of products that they say are compatible with your particular machine. It has worked on every machine that I've tested, and because you get the actual part numbers you can cross reference, though it's hardly worth it for a few bucks, especially since they guarantee compatibility if you follow their recommendation (and no, they don't push the high end gaming stuff if you don't need the performance).

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#10
In reply to #8

Re: Computer Memory DDR3, Difference Between UDIMM & DIMM

09/13/2015 11:57 AM

Ahhhh I should have mentioned that I used the Crucial memory analyser and it came up with "not known" LOL

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#11
In reply to #10

Re: Computer Memory DDR3, Difference Between UDIMM & DIMM

09/13/2015 2:27 PM

I guess that attests to their honesty... Unbuffered is usually the cheapest memory because it has less circuitry, most "ordinary" machines don't require buffered memory. The problem is usually if ECC memory is required, it's usually impossible to use non-ECC memory even if it physically fits because the BIOS checks, issues a message, and halts the boot process.

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#13
In reply to #11

Re: Computer Memory DDR3, Difference Between UDIMM & DIMM

09/14/2015 1:16 PM

In the end I phoned up Crucial technical support and after a lot of details the guy said the M58p can take both SO-DIMM and DIMM !!!

But according to the serial number he said mine takes SO-DIMM and they will guarantee it works if I buy from them, so no contest! I've bought a 4gig stick with their warranty that it will work, if not they will replace it, no quibble.

Seems this desktop has a few motherboard differences under the heading M58p.

John.

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#9

Re: Computer Memory DDR3, Difference Between UDIMM & DIMM

09/13/2015 11:22 AM

I'm So dim it's best I keep schtum. (booohooo)

jt.

Little boy steps on a butterfly, dad says "no butter for a week!"

Next day little boy stamps on a honeybee, dad says "no honey for a week!"

A few days later in the kitchen, mum stamps on a cockroach.

The little boy looks at his dad and says "are you going to tell her or shall I?"

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