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Memory Types Guide
Author: Jacob Reinhardt
Date: Mon, May 5th, 2003
Page 1: IntroductionPage 2: Theoretical Memory Bandwidth ExplainedPage 3: Two Memory Technologies and Overclocking RAMPage 4: SDR SDRAM: PC133, PC100 and PC150Page 5: DDR SDRAM: PC3700-PC1600 and everything in betweenPage 6: 16-bit RDRAM: PC1066, PC800, PC700 and PC600Page 7: 32-bit RDRAM: RIMM5300, RIMM4800, RIMM4200, and RIMM3200Page 8: Conclusion
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Introduction
If you've been to a store looking for memory, you probably found many different types. It isn't as simple as it was a few years ago when you had PC800, PC133, PC100, and PC700. To complicate things further, enthusiasts have given new names to types of memory as well (ie DDR266 for PC2100). I'm going to try to clarify what these names mean, while explaining some of their technical characteristics. I am also going to tell you what chipsets support these types; when I say support, I mean those chipsets that can actually run the memory at the speed that it was intended to run at. Without further hesitation, let's dive in.
Two names for Memory Types
There are two names that are used to refer to memory these days. Although both names refer to the same product, and each name is technically accurate, each name speaks about a distinct technical characteristic of the memory. As you prepare to digest this information, bear in mind that the key difference between the names is that one refers to the effective frequency and the other theoretical memory bandwidth.
Memory Names: Effective Freqency of Memory and DDR Signaling Explained
The new types of memory which coincided with new names really started to come when DDR (Double Data Rate) signaling first made its way into PC Memory in late 1999. Perhaps the main reason for this is because of the way DDR works. To add to the confusion ?DDR SDRAM? is not the only thing that uses DDR signaling technology. RDRAM, DDR, AGP, and modern front side bus'es use DDR signaling.
What is DDR signaling? In summary (and I am no expert), if the memory is DDR, then it transmits data two times for every Mhz. The end result is that DDR Memory will transfer twice as much data as an equally clocked SDR (Single Data Rate) Memory. Hence the name Double Data Rate. An example of this is the very first DDR SDRAM Memory, which is called PC2100. DDR buses can be referred to by their effective frequency or by their actual frequency with the suffix ?DDR? added to them. In going back to our PC2100 example, the frequency of PC2100 is referred to often as 266MHz or 133MHz DDR.
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