Buffered/Registered DRAM

[GoIon]

What's the difference between buffered & unbuffered DDRAM?
Registered & Unregistered DDRAM?
Which is better from a performance view?
Does the chipset or CPU affect the answer?

Does use of ECC or parity negatively affect the performance of DDRAM?

 

[Mucman]

I too want to know this!

From what I have heard and read is that buffered memory has a 1 clock cycle delay on all memory processes so that all data is transmitted at once. That is the reason for the extra chip on the PCB.

* HTF Disclaimer *
I probably don't know what I am talking about nor do I pretend to know what I am talking about. I am at this forum to learn, and if what I said is gibberish please correct me
* /HTF Disclaimer *

 

[CTho9305]

Mucman - I like that disclaimer mind if I steal it for my sig?

 

[DeeK]

Crucial's web site has the answers under the FAQ link:



<< DDR and SDRAM can be unbuffered or registered. EDO and FPM can be buffered or unbuffered. Buffered modules contain a buffer to help the chipset cope with the large electrical load required when the system has a lot of memory. Registered modules do not have a buffer but do contain a register that delays all information transferred to the module by one clock cycle. Buffered and registered modules are typically used only in servers and other mission-critical systems where it is extremely important that the data is properly handled. >>





<< If you already have a PC and are unsure which type you have, count the number of small, black, IC chips mounted on one of your existing DIMMs. If the number of chips is evenly divisible by three, then you need ECC. If the number of chips is NOT evenly divisible by three, you have non-parity memory.

If you are building a PC and deciding which type to use, the following guidelines should help. If you plan to use your system as a server or a similar mission critical type machine, it is to your advantage to use ECC. If you plan to use your PC for regular home, office, or gaming applications, you are better off with non-parity.

ECC (Error Checking and Correcting) performs &quot;double bit detection and single bit correction.&quot; This means that if you have a single bit memory error, the chipset and memory will find and repair the error on the fly without you knowing that it happened. If you have a double bit memory error, it will detect and report it. Using ECC decreases your PC's performance by about 2%. Current technology DRAM is very stable and memory errors are rare, so unless you have a need for ECC, you are better served with non-parity SDRAM. >>

 

[SCSIRAID]

Registered DIMMS contain hardware to redrive the address inputs to the DIMM to minimize loading on the memory bus. This is especially useful in 'double sided' parts which would have LOTS of load on the bus or in systems which have lots of DIMM sockets.

Registered DIMMS add one clock of latency to the memory access so it theoretically slows things down but not significantly.

ECC does have a small negative performance impact. This is due to writes that do not write all 8 bytes of the memory width. In this case the memory controller must read the old data, update the ECC for the new data and write the new data back. This is called Read/Modify/Write.

 

[Mikendi]

Not all chipsets/boards support ECC, or Registered ECC DIMMs. Make sure it does before buying. I'ave rtead in the case of some DDR boards if you fill all slots you need Registered RAM. Yes performance theoretically takes a minor hit, but when using programs such as StudioMax, Photoshop, and other data intensive work it's a real boon. Many high end workstation/servers use this type of memory.

 

[Noriaki]

Check the FAQ in my Signature, RAM types and terms are covered in there in more detail that I know

 

[TravisBickle]

I'm very worried that the SiS735 doesn't include support for ECC DDR. they kept quiet about this, so some websites didn't even notice. it's unthinkable to the server or phd student.
when I look at a new board, I want more than just a speed upgrade. ECC does not command a high price premium at crucial.com ... I don't want my program to be thrown every month because of an unnecessary error while it crunches.