Speed and timings

glitch

glitch

glitch

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Voltages and timings

I've read the memory stickies over and over and over, but can't seem to pull out the required answer to a few questions. Maybe I'm being particularly thick here so feel free to point me in the direction of an existing answer if that is the case.

I have a Foxconn 6150K8MA-8EKRS motherboard. In this I will be sticking an Opteron 146. I'll probably leave the Opty as it is for the first few months before getting into some overclocking action, providing I can understand what I need to do.

My board states that it accepts 2.5v DDR400 which I understand to equate to PC3200 RAM. There's a load of PC3200 memory on offer with different timings but there's also PC3500, PC3700 and PC4000 available.

My first question is about the speed of the RAM itself. As an example, if I stuck a pair of the Mushkin Redline sticks in my board, would they be running at 400MHz or 500Mhz? What defines the speed at which RAM will run?

Second question relates to voltages. Looking at something like the Mushkin HP3200 it states in the specs a voltage of 2.6V-2.8V. And looking at the OCZ PC3200 Dual Channel Gold, they state 2.8 Volts. Does this mean that I have to adjust the voltage on the motherboard to match these specs, in order to get the timings they describe, or will they run at this voltage without any adjustment from me?
 
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Anyone able to shed some light on this for me? I couldn' see either subject covered in the FAQ's, unless I'm not reading them properly.
 
OK, well that's a pretty good explanation, so I thank you from the bottom of my stairs.

What's worrying me is that I've scrimped and saved to get the cash for my new system and I want it to run as best as I can get get it to, which means getting the right kit and making the right choice first time. Unfortunately I'm hampered somewhat by my choice of motherboard, but I've got an Opteron 146 (even running it at stock will be useful) and I just need to pair the memory up with it. Price isn't an issue, within reason, as long as whatever I buy works out for me.

Am I right in saying that you are recommending the XMS3500LL because of the headroom it potentially offers?
 
I've been reading through the FAQ's and trying to get my head around them, but I'll happily admit that my knowledge amounts to very little in the overall scheme of things.

Feel free to enlighten/patronise me at your leisure - I'm always happy to learn new stuff!
 
You are a scholar and a gentleman. Your input has been really bloody useful!

Question for you: how would you get PC3500 rated RAM to run at 3500 rather than 3200? Is this to do with voltage or FSB?
 
Right, this is all starting to become clear now. You are a helpful so-and-so aren't you?

I'm quite comfortable with messing around in the BIOS, providing I know where the options are and what they do.

Within the BIOS there are options to alter Vcore, Voltage Select, VDIMM Voltage Select and a DRAM Configuration Menu (Time Mode, Memclock, CAS# Latency, etc). There's also a utility called Super Step which allows you to adjust CPU frequency, CPU Clock, CPU Ratio, etc etc. Looks like I've got everything I need.

Last question for now: Illya Kuryakin or Napoleon Solo?
 
man_from_uncle said:
Alex Waverley
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:p

Well, you have been extremely helpful and I'm very, very grateful. Never fails to amaze me just how much knowledge is swimming around the forums and how helpful people can be.
 
Just as an aside, anyone is more than welcome in this thread. Kudos to all those (especially mfu) who have taken the time to post answers. I'm sure I speak for everyone when I say you have our thanks and respect.
 
Well, having waited too long for my finances to get in shape it looks like I'll now be unable to get hold of the Opty 146, leaving me with the option of a 144 or a 148. When I've figured out what's the best option between those I'll probably pick up the RAM man_from_uncle mentioned in this thread.

Unless I shun gaming and go dual-core.
 
man_from_uncle said:
Also, in very basic terms, 'dividers' are the ratio that you run your ram at compared to your FSB (or HTT in AMD64 terms). It is not essential that the calculation for determining CPU speed be 'RAM speed' X Multiplier. You can run your ram out of time with your FSB at certain ratios. Your ram might run at 200, but if you are running a divider of 5:4 then your calculation will be 240 x multiplier. Your ram will be running slower, which will affect your processing speed in real terms, but the inhanced CPU speed will more than make up for it.

Now, on these modern boards dividers are often not represented as simple ratios like 5:4 or 6:5. Instead they are represented as as 200, 166, 133 etc. I really don't know why this approach has been taken but the numbers are themselves a reflection of the comparitive speed that the ram will run at. If you pick 166 as your divider (it's often called something like memory index in the bios) your ram will not actually run that fast, but it will run at a ratio of 166:200 to the FSB. So if you push you ram back up to 200 it will push the FSB to 240. This use of dividers allows you to reach the maximum speed of your processor without the need to run your ram at ultra high speeds.
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Sorry to dredge this up from the depths of page 4, but I wanted to ask a few more questions as I've been doing some reading up and wanted to see how if I've begun to get my head round this yet.

First off - dividers.

Now, mfu mentions above that dividers are often represented as an X:200 ratio. And by mooching around the web I've managed to find a screenshot of the relevant options in my motherboad's BIOS:



So that looks like I've got 2:1, 3:2, 6:5, 1:1, etc etc. I am right in saying that the values in that screen relate to the ratio rather than the actual memory speed itself? Because I can't see an option to actually set the speed of the RAM, so I'm assuming that the speed is set when you change the HTT frequency and use one of the dividers. Is that right?

I think we've sort of established that dividers don't affect performance as much as people might think, but I'd imagine that they do come into play when you want to get the best out of your memory - you want to run a divider that will allow you to get the best from both your processor and your memory, but not necessarily by running them at 1:1?

Second part - timings.

I'm beginning to understand what the four numbers relate to, but what I don't understand is what makes a good combination and how the memory speed comes into it. If you had memory running at 2-2-2-2 (theoretically speaking, obviously) would memory doing those timings at 200Mhz be worse than memory running at 250Mhz? Assuming for the sake of this example that some would!
 
Thanks for popping in, mfu.

OK, so with memory you need to find a set that will run with tight timings and a high frequency to get the best out of it. However, I notice from my travels that with most RAM the faster the speed gets, the slacker the timings get.

If you're buying with the intention to overclock, are you buying blind or should you already know (where possible) what your CPU is likely to overclock to and how, and then work out what RAM would partner up the best? I'm sort of getting my head around the overclocking and timing issue, but I can't figure out what people do when buying their kit. Go for the best they can afford and hope it pans out?

Let's see if my understanding of the concept is correct or complete rubbish!

Let's say I overclock a Opteron 165 (9x multi) to 275 HTT. That would work out at 2475Mhz. Let's also assume that I have a set of your Corsair XMS3500LL sticks, which run at 2-3-2-8 at 433DDR (217Mhz HTT?).

I'm guessing here that I'd either need to run a divider that allowed this (can't see one to fit exactly though) or either run a divider that gets me as close to the 433DDR as possible, or that will get the speed of the memory up a little and hope that the timings don't suffer as a result?
 
Thanks, Defcon; that confirms what I've been reading up on these past few weeks.

Jimbo; that's exactly the sort of information I've been looking for. Obviously not been looking hard enough, eh?

Off to read up some more now, cheers gents.
 
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