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sdram-rdram-ddram?

Posted on 2002-05-07
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what's difference between sdram,rdram and ddram?
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Question by:yazan3000
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SDRAM - Synchronous Dynamic Random Access Memory
RDRAM - RAMBUS Dynamic Random Access Memory
DDRAM - Double-Datarate Random Access Memory

SDRAM is the most common type.  These days it's more often called PC100 or PC133 (indicating its speed rating) and is a specific type of RAM module.

RDRAM is a proprietary design patented by RAMBUS Corporation and heavily supported by Intel.  It's a completely different scheme than SDRAM that provides a promise of greater RAM speed by being more in "tune" with the way a modern CPU access memory.  Priced somewhat to significantly higher than SDRAM and in some cases does give a performance boost in proportion to its greater cost.

DDRAM is a variation of the SDRAM scheme primarily supported by AMD as an alternative to the higher priced and patent protected RAMBUS RDRAM design.  This is essentially SDRAM running at 2X speeds, most commonly at 233 or 266MHz today.

Which is best?  It's hard to say since all have their pros and cons and high performance systems can be built using any of the above.  If you already own a computer, you really don't have an option.  You must use the type that your computer is designed to take.
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Below P IV-2GHz new DDR333 (166 MHz) nearly equals RDRAM's performance. At higher speeds RDRAM could/should finally make a bit of a difference (and only in powerful memory intensive applications).

Difference between SDR (single-) and DDR (double data rate) is the moment that data is actually written. Imagine a block wave signal. Data can be written when signal "drops" (could be exactly opposite but that detail doesn't matter now). It would take an entire frequency cycle (though the signal coming back "up" again) before another "drop" appears and memory can be written again. DDR can be written on both signal changes, thus, at the same frequency, it can handle twice as much data!

Another important difference: RDRAM is more expensive!
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