Question about memory speeds

[The Coder]

I am looking into building a PC. This will be the first time I have done this. I have a Dell now but my recent visit to their site was disappointing. Anyways I am reseraching all I can about every piece of hardware I will need. I am deciding what kind of motherboard to buy and one of the factors I am looking at is the type of memory I will want to use. SDRAM is old, not using that, RDRAM looks like it is too expensive and going by the way side. So the 2 memory types I see is DDR and DDR2(slowely emerging). Now lets say I go for a motherboard that supports DDR ram. Does this mean that the board can handle any speed DDR ram? For example can a board handle DDR 200 MHz/PC1600 and DDR 400 MHz/PC3200? If a given board can only support one speed, it is best to go with a board that can handle the fastest speed RAM of that type, correct?

[cybertron]

Yep, as long as it supports a 400 Mhz FSB speed, then it will do fine with all memory up to at least PC 3200. If it supports only up to 333 FSB, then it will go up to PC 2700, and so on. However, a DDR motherboard won't work with DDR2 to the best of my knowledge. I'm not sure if DDR2 is backwards compatible either.

[The Coder]

Ok, that makes sense. But what if a motherboard says it can handle 2100 but you use a 3200? You can't do that correct?

[ph34r]

Your RAM can be faster than what the mobo supports, but not vice versa. Sorta like driving a Porsche in a parking lot vs. driving a go-kart on the interstate.

[cybertron]

Yeah, your 3200 will just run at 2100 instead of its rated speed.

[The Coder]

Thanks guys, everything you have said so far makes sense. One more question. Suppose I have 2 DIMM slots, do I have to put the same speed memory in each?

[DSwain]

I believe you do need to. In some cases, you can run slower memory (if it's all the same) and the board will just know to run the memory at a slower clock, but in the case of mix-matching memory, I think you have to keep it all matching. That would make more sense anyways I would think.

[cybertron]

I've heard, completely second-hand, that you can run two different speed sticks and it will just run them both at the slower speed, but frankly even if you can do that it's definitely safer not to. Memory tends to be touchy about things like that. Hence why people often recommend not even mixing brands of the same type, much less anything else.

[ladoga]

Originally posted by cybertron
I've heard, completely second-hand, that you can run two different speed sticks and it will just run them both at the slower speed, but frankly even if you can do that it's definitely safer not to. Memory tends to be touchy about things like that. Hence why people often recommend not even mixing brands of the same type, much less anything else.

I have two different speed sticks. They work at speed of slower one. 64mb PC100 and 128mb PC133 SDRAM of different manufacturers. No problems whatsoever. I have ordered 512mb PC133 chip tho as 192mb of memory isnt enough.

I think only real restrictions are maximum speed supported by mobo and memory type (SDRAM, DDR, DDR2).

Id go for 533MHz DDR if i was building a new puter. Faster memory isnt usually any more expensive than slower one, prices seem to go more with availability.

I doubt there is any noticeable difference if you choose 400MHz ddr tho. So if you decide to buy mobo which supports 400MHz sticks and if it's cheaper than 533MHz sticks it would a good choice too.

Remember to run a memory test when you get your new pc together to check if it works allright. Large amount of memory sold is not working as it should. If theres any problem just return the defect stick and get a new one. This is normal. Thats why most memory manufacturers give good guarantees.