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Q: What does DDR stand for and what does it do?

 

A: DDR stands for Double Data Rate. Most (pretty much all) memory you can buy now will be DDR. The following explains the basic electronic principle behind it.. and how it makes your computer faster (all important) -

 

Basically, older SDR (single data rate) memory could only be triggered to execute commands (for want of a better description) on either the leading or falling edge of a clock pulse.

 

So what is a clock pulse then? -

 

A clock pulse is basically a change of the voltage state from negative (usually 0v) to positive (a + voltage) and back again. The number of times this happens in a second is the frequency.. measured in Hz. So a frequency of 200mhz say will mean this is happening 200 Million times in a second.. fast, yes. (I hope you are still following).

Ok.. so now then.

A leading edge of a clock pulse occurs when the voltage changes from - to + (think of a straight line going up.. if you've ever used an oscilloscope you'll know what I mean.) and a falling edge occurs when the voltage changes from + to - ( a line going down).

 

So SDR memory could only execute commands on one of those instances.. either leading or falling edge.

 

DDR memory basically takes advantage of both the leading and falling edges of the clock pulse.. executing on both (twice the commands in the same amount of time). Hence why for DDR memory the stated frequency is multiplied by two.. 200mhz becomes 400mhz etc. Obvioulsy, being able to perform twice the number of commands in the same time frame gives a great boost to the performance of your memory, and hence your computer as a whole.

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  • 3 weeks later...
Is it written in stone, that memory for Dual Channel must be bought at the same time in pairs?? Or can I still get away with purchasing one stick now and another later?? :blink:

A: Nearly all memory of the same speed can run in dual channel. If you tried to run two different speeds the speed would be of the slower stick.

 

For maximum stability and therefore maximum overclocking potential, people try to match their sticks as closely as possible. The dual channel kits you see for sale usually have two sticks picked at about the same time in the production run, so they are (theoretically) as close to identical as they can get. Buying two sticks of the same brand, size, and speed should be sufficient.

 

Buying one stick now and one stick later may or may not cause problems, it would depend on the RAM. Some companies will keep a product name, for example Kingston HyperX PC3200, yet the same model can be built with different chips depending on availability.

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DDR is double data rate, totlay different form dual channel.

 

I am currently using DDR in single channel.

 

To work in dual channel you need a motherboard that supports it that supports it and 2 (preferably identical) sticks of ram.

Edited by oralpain

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