Components for Building Computers From Scratch/DIMM


QUESTION: Am I right that the 168 Pin DIMMs are SDR?
And this Means Single Data Rate?

And when the 184 Pin DIMMs came out they SDR but now it ment
synchronous dynamic ram?

ANSWER: Not quite - it's a somewhat confusing history. Technically what is colloquially called "SDRAM" ("Single Data Rate RAM") is termed "SDR SDRAM" - Single Data Rate Synchronous Dynamic Random Access Memory. "DDR RAM" is properly "DDR SDRAM" - Dual/Double Data Rate Synchronous Dynamic Random Access Memory. In written and spoken convention, however, "SDRAM" almost always refers to single data rate memory, such as would be found on a 168-pin DIMM, and "DDR" references double data rate memory (e.g. 184 pin DIMM).

Both technologies are based on SDRAM, as opposed to asynchronous memory technologies (e.g. FPM, EDO, BEDO), and when SDRAM originally appeared (as SDR SDRAM) it was called "SDRAM" (referencing "Synchronous Dynamic RAM"), to delineate it from EDO memory which was (at the time) common, and over time this has been altered to reference "single data rate" with the introduction of successive dual data rate generations (e.g. DDR1-4).

If you have further questions, feel free to ask.


---------- FOLLOW-UP ----------

QUESTION: So if I get what you are telling me

DDR1. and DDR2. and DDR3. are all called SDR SDRAM  
Single Data Rate Synchronous Dynamic Random Access Memory?

No - all of the successive generations of DDR are properly called "DDR SDRAM" as they are synchronous rate DRAM, but operate at dual data rate (data transferred at the top and bottom of the clock). The successive generations just add a number to identify themselves as distinct, but still a member of the DDR SDRAM family of technologies.


Components for Building Computers From Scratch

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