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Old 12-23-2005, 04:44 AM   #1
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Default How FB-DIMM Memories Work

There has been a new article posted.

Title: How FB-DIMM Memories Work
URL: http://www.hardwaresecrets.com/article/266

Here is a snippet:
"FB-DIMM (Fully Buffered DIMM) is a memory module technology targeted to servers developed recently created in order to increase the memory speed and the maximum memory capacity of a server. In this tu..."

Comments on this article are welcome.

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Old 06-01-2012, 11:45 PM   #2
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Default Fully-Buffered vs Registered

Hello everyone! I've just read the tutorial on how FB-DIMMs work, and I've been wondering what's the difference between this memory and the registered one? and wich one is better?

Can someone explain in an easy way?

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Old 06-03-2012, 01:42 PM   #3
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FB-DIMM is a completely different architecture, using serial communications. Registered modules are regular DDR memories with a buffer chip added, using parallel communications.
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Old 06-03-2012, 10:20 PM   #4
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Yes after reading the article I understood that serial communication was in order to expand memory capacity and to access memory in several channels. What I really don't get very much, is the function of the buffer which is seen in the images on the article.

Non buffer modules, are the same but with no buffer.

So on the other hand, non-registered modules are standard DDR modules using parallel communication.

Registered ones, are the same but with the buffer chip in the module, which I bring back the same question, what's this buffer function?

If I had to take a guess, I would say it provides ECC or parity

On a different subject, you once recommend me a PC architecture book, I'm gonna buy "Upgrading and Repairing PCs" from Scott Mueller, I think that would be a great book to read and learn, based on the critics!
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Old 06-04-2012, 01:27 PM   #5
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The memory bus only allows a certain number of components (i.e., memory chips) to be attached to it. This limits the maximum amount of memory that you can connect to the memory bus. The buffer chip, which is added between the memory bus and the memory chips, expands the number of memory chips that can be attached to the memory bus, therefore increasing the maximum memory capacity available. Memory modules with a buffer chip are more expensive and are targeted to servers.
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Old 06-04-2012, 09:03 PM   #6
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Ok, all clear now except the difference between the FB and non-buffer modules, I just can say, well, that the non-buffer has no buffer D:
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Old 06-06-2012, 02:01 AM   #7
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Non-buffer or "unregistered" are conventional memory modules, without a buffer chip. All modules targeted to end-users are non-buffer models. FB-DIMM refers to the technology of data transmission (serial instead of parallel).
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Old 06-06-2012, 11:12 PM   #8
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I just love how the internet is full with different replies or concepts about this subject, for example:

"Q: What are the differences between registered/buffered/unbuffered memory modules?
A: Registered modules have additional registers, which delay all addressess transferred to the module by one cycle. This is done to decouple the ram chips from the memory bus, so a module can have more chips (the bus load will not increase if more ram chips are present). Because of that, registered modules are available in higher capacities, but of course you can't use these high capacity modules on a bx-based board. You can recognize registered modules physically by looking at them. If there are one or more (small) chips on them apart from the ram chips, then it is a registered module.
Buffered modules are similar, but instead of registers, they contain buffers, the difference is that a register is clocked, and a buffer is not. EDO and FPM modules can be buffered or unbuffered, and sdram modules can be registered or unbuffered (the term unregistered is sometimes used too)."

Or:

"EDO (Enhanced Data Output) and FPM (Fast Page Mode) modules can be buffered or unbuffered. Buffered modules contain a buffer to help the motherboard cope with the electrical load when the system has a lot of memory.

DDR (Double Data Rate) and SDRAM (Sync Data Random Access Module) modules are either unbuffered or registered. Registered modules have a register that delays the transfer of data by one clock cycle"

And about the buffer:

"These smaller chips on registered RAM work as a buffer, or a place for the data to be stored while the module is waiting to use the information. This effect reduces the errors caused by excessive power demands on the module, helping ensure that information is not lost."

Different replies or concepts compared to the one you gave me, I'm not saying you're wrong, it just confuses me a little bit, because it's just not the same.
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Old 06-08-2012, 02:53 PM   #9
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These explanations are correct; I tried to simplify, as both buffered and registered modules have the same goal, to expand the number of chips you can add to the memory bus.
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