# RAM types Explained



## Tobywuk (Aug 14, 2006)

hi,

Im just curious about the diffrent types of ram that are currently available on the market. Im just wondering if someone could explain.

What is DDR2 and what is the diffrence between this an normal DDR?
what about SDR? 
and what do they stand for? 
how about the "PC300" bit and the "400mhz" part of the spec?
how do you tell what is better? would they make much diffrence?
also if you have more than one stick in a machiene would they have to be matching? or is it better if there matching? do the sticks have to be the same "PC****"

I would apreciate if someone could explain so i can understand it all more clearly. thank you


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## Inactive (Apr 11, 2005)

DDR is Double Data Rate and works twice as fast as SDR (Single Data Rate).
DDR2 is physically bigger than DDR, so they are not interchangable and likewise with SDR. it is physically smaller again. DDR runs upto 400MHz and DDR2 runs at faster speeds again. 

i cannot remember exacty where the PC3200 came from, but just divide it by 8 and it will tell you it's 400MHz. so PC2700 is 333MHz. i have only ever heard the SDR measured in the MHz it runs at, such as PC133, which runs at 133MHz.

generally the faster it runs the better it is. going from 333MHz to 400MHz you might not notice any difference, but if you are going to upgrade you are restricted to what the mobo can use. crucial is a good website to goto to find out what you mobo can take.

it is always adviced to keep the same speeds in one mobo. while the faster memory generally slows down to match the slowest memory DIMM, sometimes they will not run side by side properly.


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## booyah188 (May 24, 2006)

hmm and what is single and dual channel memory? what does that mean?


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## Inactive (Apr 11, 2005)

http://www.kingston.com/newtech/MKF_520DDRWhitepaper.pdf


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## MunkyPhil (Apr 7, 2006)

Just to add to what Freddyhard said, PC3200 comes from the 3.2Gb/s bandwidth and DDR RAM goes up to a maximum of PC4200 (I think), which is DDR533.

Dual channel is a function of motherboards which doubles the bandwidth of the RAM, so two PC3200 sticks in the right configuration would have a bandwidth of 6.4Gb/s instead of 3.2GB/s. PC3200 would still run at 400MHz though so this only equates to a 15-20% performance increase.


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## ebackhus (Apr 21, 2005)

Another thing about DDR2 is that it has MUCH higher latencies which, to some, make it not worth the upgrade from DDR.

The most common problem with getting RAM is putting it into the PC and having it run at maximum speed. Intel systems rely on the Northbridge chip to handle memory access and data transfer. If the chipset isn't designed to run at the maximum speed of the RAM then you lose bandwidth. It's like adding mods to a Honda, but not nearly as ineffective. AMD chips from the socket 754 and up have on-die memory controllers. This allows the CPU to talk directly with the RAM and to get data from it MUCH faster.


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