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Need help choosing DDR Please


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I just purchased the following:


DFI nF4 Ultra-D

Opteron 170


Next I need to pick out some DDR that has good potential for overclocking my Opteron a bit. I'm not looking to take it to the extreme edge, just somewhere in the middle of it's range would be nice. The CPU is a CCBWE 0543TPMW, so I'm not totally sure what that range is.


My questions about DDR:


1) Should I get 2 x 1GB or 2 x 512mb? I really would like 2gb of ram, so hopefully something out there has the potential for overclocking.


2) I'm totally clueless on timings, even after reading a bit. I'm just looking for stability in my overclock and hopefully not totally losing out on the speed of the ram. Can I have my cake and eat it too or do you trade one for the other?


3) Should I be looking at DDR 400 or DDR 500 for OC?


4) Which brands should I stick with? OCZ? Patriot? Corsair? Mushkin? Geil? G. Skill? Any others?


5) How about models? Platinum? Gold? Performance? Value?


BOTTOM LINE: What can I get for $200 - $250 that will provide good OC and good speed?


Thanks for any input. You guys really sound like you know what you're doing.

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Thanks for the reply Sharp. The G. Skill was one of the ones I was thinking about because of another forum post I read. Here's another I was thinking about:


mushkin eXtreme Performance 2GB PC4000



Is the G. SKill still the better choice?


These ram choices are both Cas3...Mushkin=3-4-3-8...G. Skill=3-4-4-8. Doesn't these timings mean that it's relatively slow memory or is this pretty much my only choice if I want 2 x 1gb sticks and to overclock? Or do the timings get a little tighter and faster when I start overclocking? This is the confusing part to me.


I've seen OZC 2GB Dual Channel Platinum with 2-3-2-5



I know this would be faster, but would it not be as good for overclocking?


Just trying to learn at the same time I'm solving my choice dilemma.


Thanks so much for the help.

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I will try to explain.


Lower memory timings = faster but, The timings are related to the frequency at which you run the modules at.


E.g, PC3200 200Mhz/400DDR 2-2-2-5.


Each number means Clock cyles.

Clock cycles = A measurement of time based on the frequency


So the first 2 = 2 clock cycles @200Mhz

Last number = 5 clock cycles @200Mhz


What is a (or 1) clock cycle?


Looking at that, it is a pulse of voltage from high to low over a period of time.

And as said in the nf4 advise guide, 1 cycle per second = 1Hz.


Anyway, I will skip the details and keep it simple,


2 clock cycles @200Mhz is not the same as 2 clock cycles @250Mhz.


200Mhz = 5 nano-seconds

250Mhz = 4 nano-seconds

300Mhz = 3.33 nano-seconds


# So 2 clock cycles at 200Mhz = 10 nano-seconds (2x5ns)

# And 2 clock cycles at 250Mhz = 8 nano-seconds (2x4ns)


The smaller the time in nano seconds, the faster the memory chip can read/write data.


Suppose you had a module that was rated 3-3-3-8 @300Mhz (PC4800).

Would it be faster than a module rated 2-2-2-5 @200Mhz (PC3200)?


3-3-3-8 PC4800 module

3 = 9.99ns

3 = 9.99ns

3 = 9.99ns

8 = 26.64ns

Total latency = 56.61ns


2-2-2-5 PC3200 module

2 = 10ns

2 = 10ns

2 = 10ns

5 = 25ns

Total latency = 55ns


Both are the same.


# Usually as you increase (overclock) the frequency you must increase the memory timings.

# And as the memory gets bigger (512MB to 1024MB) the timings must increase as it will take longer to search more space. (MB = space, more MB = more space), so the memory takes longer to search.


This is just to give an idea of the overall latency

The 2x1GB OCZ platinum 2-3-2-5 is rated 200Mhz.

2 = 10ns

3 = 15ns

2 = 10ns

5 = 25ns

Total Latency =60ns


The 2x1GB G.Skill 3-4-4-8 is rated 250Mhz.

3 = 12ns

4 = 16ns

4 = 16ns

8 = 32ns

Total Latency =76ns


The 2x1GB G.Skill @200Mhz should be capable of 2.5-3-3-6

2.5 = 12.5ns

3 = 15ns

3 = 15ns

6 = 30ns

Total Latency =72.5ns


So overall the OCZ platinum PC3200 2x1GB kit is 12.5ns faster than the G.Skill kit at 200Mhz and 16ns faster when the G.Skill is running at 250Mhz. (The difference is very very small)


But there is more to it than that.

# When you overclock your CPU the data rate increases therefore it can send more data to the memory in one go. Should your CPU go beyond 6400MB/s then PC3200 is going to be causing a small bottle neck.


Just remember

# The timings (clock cycles) = latency based on frequency.

# Lower timings at the same frequency = faster.

(Mushkin PC4000 2x1GB kit is faster than the G.skill PC4000 2x1GB kit)

# PC4000 vs PC3200 = only faster if you OC.

(So the OCZ platinum PC3200 2x1GB kit is better for non-overclockers)



A lot of people will argue that on the A64 chip low latency modules are not worth the price and a PC4000 2x1GB kit is going to offer a very small and in some places 0 performance increase compared to a PC3200 2x1Gb kit.


My views,

# For 2x512MB always get a 2-2-2-X rated PC3200 kit.

# For 2x1GB go for PC4000 and don't spend too much on one rated 3-4-3-8 vs 3-4-4-8.

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