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E.g. Samsung 2GB 2Rx8 PC2-6400S-666-12-E3.

According to https://en.wikipedia.org/wiki/DDR2_SDRAM#Chips_and_modules :

  • PC2 - DDR2
  • 6400 - theoretical bandwidth in MB/s, corresponds to base frequency (6400 corresponds to DDR2-400)
  • S - SO-DIMM

What are the others? 666-12 looks like timings, E looks like speed class from the same table @Wikipedia (corresponds to part of the timings), what is 3 and 2Rx8, I've no idea.

(The reason for asking is to find out which of these letters and numbers must match for the modules to be able to run in Dual Channel mode w/o slowing each other down. I still wish to know the meaning of the description though.)

EDIT: I've looked though the suggested duplicates, namely: RAM Part Numbers - Meaning?, How do I interpret the specification of memory (RAM)?, Meaning of last 4 digits in a Samsung RAM memory stick, How can I tell what RAM will fit my computer? - and none explains this particular designation.

ivan_pozdeev
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    The answer is as many as possible for best results. Usually you can just buy packs of modules that will match. Though that might be hard for DDR2. As you already said the 12 is likely timing. The 2Rx8, as per the item description, will reference "8 modules per sides on two sides". – Seth May 31 '17 at 11:27
  • It could simply be an internal model number assigned by Samsung. As @Seth notes, there is no way to tell what is the specific correct answer except to query Samsung. This site is not a source for official Samsung information. There are already questions and answers on this site that give answers how to decide the correct RAM for use in your computer. – music2myear May 31 '17 at 23:05
  • @music2myear So, you're claiming that this is not a standard format but Samsung's private one? This doesn't seem likely: https://www.avito.ru/moskva/tovary_dlya_kompyutera/nanya_2gb_2rx8_pc2-6400s-666-13-f1_so-dimm_ddr2_714528196 – ivan_pozdeev Jun 01 '17 at 06:08
  • No. Please read my comment carefully. I started that it COULD be that. Among other evidence is Ramhounds comment on the one answer below where it is clear the most likely meaning is not correct. Further your actual question is "what RAM fits my system" which is answered elsewhere. – music2myear Jun 01 '17 at 14:12

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666/666.67/667 are typical data rates for DDR2 in MT/s.

666 is the data rate of an i/o bus clock of a 333Mhz module, which would be called PC2-5300.

12 is CAS latency in ns.

For the 'x' and 'DR', look at my previous answer here.

If you want to run in dual channel, best practice is to have identical modules. If one has worse specs (in MHz or timings), the channel will run at the lowest specs of the 2 modules.

Overmind
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  • Since 666/666.67/667 is the data rate of a PC2-5300 and the example is a PC2-6400, the first two paragraphs can't be true. – ivan_pozdeev May 31 '17 at 13:42
  • A PC2-6400 can work at 667, does not have to be set at 800. But a combination of 6400 and 667 looks like a miss-labeling to me, or it can refer to a recommended JDEC setting. – Overmind Jun 07 '17 at 11:56