What is the actually difference between UDIMM and DIMM?

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Cyrus00

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I've been searching for this answer for awhile now, and have yet to get a clear/concise answer. Between these forums and other tech forums, I've found conflicting answers. Some say there is no difference, while others say there is. One particular answer in these forums, state UDIMM is for workstations only. I found nothing to support this.
Here's a breakdown of my current understanding of DIMM:

There's four mainstream types of DIMM:

1. UDIMM - Unbuffered/Unregistered

2. RDIMM - Buffered/Registered

3. FBDIMM- Fully Buffered

4. SO-DIMM - laptop ram

And "DIMM" is actually just the generic form factor name, which is used to refer to consumer/desktop grade unbuffered ram, aka UDIMM.

Am I wrong in my assumption? If so, then what is the actually difference?



Isn't DIMM the same as UDIMM? Just that companies don't refer to it as UDIMM like they should?
 

Cyrus00

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The wiki doesn't answer my question (at least I don't see where it did). I've checked both of the relevant pages on DIMM, and on unbuffered/registered memory, and they both don't specify a difference between UDIMM and DIMM. Seems like DIMM is always referred to as the form-factor, rather than a specific type among the 4 I mentioned earlier.

The 64 bit data path, is referred to as a difference between SIMM and DIMM, or RDIMM and DIMM, but not between UDIMM and DIMM. It's the same for pin number.
 
G

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Well i heard that both udimm and dimm rams can be used in AMD boards. Soon i will check it with asus sabertooth. box says dimm memory but since its consumer board and I have udimm memory it should work. As for the Intel boards I think you ll need Dimm just to be safe but im not familiar with intel boards so good luck in searching
 

Pinhedd

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UDIMM is a subtype of DIMM.

DIMM stands for Dual Inline Memory Module.

Dual = the electrical contacts on each side of the PCB are unique signals. On SIMMs they are shorted together.

Inline = all electrical contacts lay along a straight line

memory module = self explanatory.

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).

Fully Buffered DIMMs, or FB-DIMMs, are an obsolete form of memory module that are not compatible with other types. DDR2-FBDIMMs can still be found, but no DDR3 variant exists.

In case this is a little bit confusing, there is no such specific thing as a DIMM. All DIMMs can be further classified into a more specific type. Most memory that you will find at consumer electronic shops right now are DDR3-UDIMMs. DDR4-UDIMMs have recently become available as Intel introduced the LGA-2011-3 platform. Online retailers that also deal in servers and workstations will also sell DDR3-RDIMMs and DDR4-RDIMMs.

In consumer parlance, UDIMM is often used synonymously with DIMM.
 
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