memory speeds and latencies

[f0rbez]

I've been trying to read some stuff about memory speeds and stuff but I'm kind of confused. I have an Intel D875PBZ mobo with an 800mhz fsb, and its suppose to support ddr400 with an 800mhz bus, and only ddr333 with a 533mhz bus. What I dont get is if these are the highest memory speeds supported, how come there are so many faster memory speeds? ddr500 for example.. i wouldnt be able to use that would i?

also memory latencies confuse the hell out of me. how much do they really matter? when i bought my pc from alienware, there was only one type of memory available. shortly after, corsair xms memory was available at a significantly higher price. the memory i have is samsung and i think the latencies are 3.0-3-3-8 (if i read them from bios correctly). Now im wondering if I should have gotten memory with lower latencies, like the corsair xms.

how is my current latency, good or bad? should i consider trying to get different memory?

 

[Crashman]

If you're running an 800 bus CPU, it's best to have 2 DDR400 (PC3200) DIMMs running in Dual Channel mode. Faster memory is for overclocking, which is extremely limitted on your board.

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[f0rbez]

thats what i have

 

[jammydodger]

With your system speed will be more important than low latencies because P4's are very bandwidth hungry. While AMD cpu's benefit far more from low latencies.

Here is an analogy I gave to someone else explaining how latency effects performance:
Imagine RAM as a big warehouse, now if a worker needs to get lots of items all from the same place it would be very helpfull if he could carry lots of things at once (transfer a lot of data at one time). However if he has to go to lots of different places in the warehouse to get lots of small items it really doesnt matter how much he carrys. What does matter is how fast he can locate the item in the warehouse, this is where latency comes in. When ever a different location in RAM needs to be address there is a certain ammount of time that the RAM has to wait while address' are put on to RAS and CAS pins.
In summary, low latencies are good in some situations while high bandwidth is better in others.


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[f0rbez]

thanks thats a bit easier to understand. could you give any example situations for which one is better than the other?

 

[jammydodger]

When using large files such as videos or high quality pictures, bandwidth is more important. This is cause the whole file will be kept contiguously.
Running applications that use a lot of small files (web browsers for example) will prob perform better at low latencies (although web browsing is not really a demanding task so you wont notice the difference).

Its hard to say with games, It depends how they have been programmed. The size of textures etc. Im not a programmer so I wouldnt like to comment.

If your going AMD def get low latency, if you are going P4 then it doesnt really matter as much.

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