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Speed and timings

Discussion in 'Memory' started by glitch, 15 Jan 2006.

  1. glitch

    Mobster

    Joined: 8 Nov 2005

    Posts: 4,385

    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?
     
    Last edited: 17 Jan 2006
  2. glitch

    Mobster

    Joined: 8 Nov 2005

    Posts: 4,385

    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.
     
  3. Bri62

    Hitman

    Joined: 6 Oct 2004

    Posts: 664

    Location: Widnes, Cheshire

    your ram speeds are set by your fsb speeds (unless you use a divider) so @ 1:1 if your fsb is @250 so will your ram and second you set you voltage in the bios there will be a standard but you may need to up the voltage to get it more stable, voltages stated are max for that ram, in your case your max voltage is 2.5v governed by your mobo
     
  4. man_from_uncle

    Wise Guy

    Joined: 9 Jan 2006

    Posts: 1,345

    ram speeds are misleading to most people to start with. If ram is PC4000 that means it CAN run at DDR500 without being considered 'overclocked'. However your computer will almost certainly default it to run at PC3200 speeds (or PC2700 with older CPUs).

    The speed rating of ram is like the speed rating of car tyres (I can't remember where i read this metaphor, but it is apt). A tyre that's rated to run at 90mph almost certainly can run faster than that if the rest of the car pushes it to, however there is no guarantee of this and it probably won't be all that stable or safe. A tyre rated to run 120mph however will do faster speeds because it has been designed to. That does not mean that the 120mph tyre automatically does them, just that it is capable of doing them. RAM is the same. Getting some PC4000 is pointless unless you plan to overclock and even then some good PC3200 will get up to PC4000 speeds if you really push it (though it's not guaranteed).

    Corsair XMS3500LL is a good option in my opinion. It's got overclocking capacity and it runs very well at PC3200 speeds. However it's really bloody expensive.
     
  5. glitch

    Mobster

    Joined: 8 Nov 2005

    Posts: 4,385

    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?
     
  6. man_from_uncle

    Wise Guy

    Joined: 9 Jan 2006

    Posts: 1,345

    Though XMS3500LL is not GUARANTEED to run past 218mhz, i've had it at 260 with pretty good timings and i certainly have not pushed it as far as it will go. It's also good because even if you never run it past PC3200 it'll still outperform almost every other 2 gig set.

    Do you know about ram timings?
     
  7. glitch

    Mobster

    Joined: 8 Nov 2005

    Posts: 4,385

    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!
     
  8. Jimbo Mahoney

    Soldato

    Joined: 18 Oct 2002

    Posts: 6,197

    Location: Belfast

    On the AMD64 platform, I wouldn't bother spending too much on the memory.

    Just get some that can do tight timings at stock speed and forget about it.

    Something like 2-2-2-6, 1T @ 200 Mhz will be fine.

    Unless your motherboard doesn't offer much flexibility as far as dividers go, that is.
     
  9. man_from_uncle

    Wise Guy

    Joined: 9 Jan 2006

    Posts: 1,345

    Well, i know the basics, and that's probably enough to give you an idea.

    When the CPU wants to access information from the RAM it takes a certian amount of time. It takes time to find the information, time to get to it, time to grab it, time recover it etc. We are only talking a few cycles or so for most these procedures, but the fewer there are per task the faster overall the system will run. RAM timings represent how quickly these little procedures take, and the lower the timings the quicker. There are something like 20 different timings involved but most people only focus on the main 4 (sometimes only the 1 in fact). These 4 timings are represented most commonly something like this 3-4-4-8, 2.5-3-3-7, 2-2-2-5 etc.

    Now, bog standard ram will normally run at PC3200 with 3-3-3-8 timings. Good ram will run at 2-2-2-5. However, the larger the amount of ram and the more sticks involved, the more difficult it is to keep these numbers low. Getting 2-2-2-5 with 2 sticks of 512mb at PC3200 is A LOT EASIER than getting 2-2-2-5 with 2 1gig sticks. In fact I think the fastest 2x1gig set of ram only runs ar 2-3-2-5 at PC3200. (as a minor aside the reason I am talking about sets of ram rather than individual sticks is because a 2 stick set will tend to run faster than 1 stick with the same capacity. This has nothing to do with timings though).

    Another factor with ram timings is that they are harder to keep low if the ram runs faster. So getting 3-3-3-8 at PC3200 might not be great, but at PC4000 it's not too bad at all.

    I won't go into details about exactly what each of these 4 numbers means (because I am only moderately aware myself) but i will explain CAS. The first number on the 4 (and often the lowest) is called CAS. It is generally considered the most important of the timings and some sticks of RAM only advertise this timing. CAS 3 is the worst (though you can actually go higher) and CAS 2 is the best. I think Geil actually made some CAS 1.5 sticks, but there is virtually no difference between 2 and 1.5. Having said all that it is becoming increasingly apparent that CAS is not actually more important than some of its brothers.

    Finally and most confusingly, some makers of ram, as well as some overclockers and computer geeks, don't use the same order of timings. They may say 8-3-4-3 or some other combination. Generally speaking though the lowest number is likely to be the CAS value.

    The XMS3500LL i mentioned runs at 2-3-2-6 at PC3500 speeds, which is very good indeed for a 2 gig set. At PC3200 speeds it can be pushed to be a little faster, but that's not a guarantee and it might need some extra volts.

    Hope that helps.
     
  10. glitch

    Mobster

    Joined: 8 Nov 2005

    Posts: 4,385

    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?
     
  11. man_from_uncle

    Wise Guy

    Joined: 9 Jan 2006

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    This is to do with FSB (though technically it is no longer FSB as AMD moved the memory controller onto the cpu) and potentially volts as well. To get to PC3500 speeds you need to use your BIOS. Sadly they are all different and i have never even heard of your motherboard so I can't tell you where the setting is.

    However I can tell you what it will look like. Somewhere in there you'll see something called somthing like CPU speed or maybe HTT speed or perhaps something else, but certainly related to speed or frequency. It will be set as a default to 200 (or potentially 400 if they are doubling it, but probably 200). You'll need to raise this number to 218 to get to PC3500 speeds. However your CPU will not be expecting this boost of speed so you may need to raise the vcore (which is the voltage to the CPU)which will be set as a default to something like 1.40-1.45. Raise it up by no more than 0.5 volts. Save your changes and you should see that your processor is now running about 9% faster.

    3 things to note though. Number 1, it might not work. I have no idea what that motherboard is capable of nor do i know what options it has in its BIOS. Number 2, if it goes wrong and you cannot even get back to the BIOS to change it back you may have to use the reset switch on the motherboard. Again, i can't tell you where that is or what it looks like as I don't know the motherboard. Number 3, the standard fan on top on that 146 should be more than adequate to go up 9% or so but probably not that much more and even 9% is not a certainty. Overclocking the CPU makes it hotter and with heat comes instability.

    Good luck and have a second computer ready to get online should you need to ask for more advice while overclocking.
     
  12. glitch

    Mobster

    Joined: 8 Nov 2005

    Posts: 4,385

    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?
     
  13. man_from_uncle

    Wise Guy

    Joined: 9 Jan 2006

    Posts: 1,345

    Alex Waverley
     
  14. man_from_uncle

    Wise Guy

    Joined: 9 Jan 2006

    Posts: 1,345

    By the way, it's my pleasure to help. I actually only built my first rig this weekend and as such took effectively a 2 month crash course learning about overclocking and hardware. As it is, everything turned out as well as I could have hoped for; but it would not have been so if i'd not got help from people on this forum and a couple others.
     
  15. glitch

    Mobster

    Joined: 8 Nov 2005

    Posts: 4,385

    :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.
     
  16. HangTime

    Man of Honour

    Joined: 25 Oct 2002

    Posts: 28,065

    Location: Hampshire

    I notice that you are getting an Opteron CPU, and claim that you will be leaving it for a few months before overclocking it - a fiver says you won't be able to resist the urge! :)

    Because the opterons are such good clockers, you will likely be reaching quite a high FSB, meaning that there is an advantage in getting high speed RAM (PC4000 and above). For ordinary systems, as someone else mentioned, simple pc3200 with good timings is very effective, but when running high fsb it can be worthwhile getting something a bit faster.

    There's a common myth that FSB doesn't really matter and that timings are everything on the A64 platform, but this isn't the case, they are both important. For instance, I find that my system performs just as well at 255mhz, 2.5-4-8-3 as it does at 232mhz, 2-3-6-3 (cpu speed kept the same of course). I've conducted a whole bunch of tests and found that there's more than one way to cook an egg - it's all about finding the best balance, rather than going all-out for the lowest timings.
     
  17. man_from_uncle

    Wise Guy

    Joined: 9 Jan 2006

    Posts: 1,345

    I agree with hangtime, a good combination of timings and FSB does seem to produce better results than merely tighter timings or higher FSB alone. There's a sweet spot with every set of ram. I took just under 3 mins off my superpi 32m by raising my divider back to 166 from 133 (luckily my ram could handle the jump and stick to the same timings)

    Glitch, don't worry about dividers for now. We'll get onto that in the next lesson.
     
  18. peetee

    Soldato

    Joined: 18 Aug 2004

    Posts: 6,741

    Location: The Toilet

    you lot are so helpful, i think ill overclock next week :D and ill go with the 3500corsair if its compatible with my shuttle, since i wont be heavily overclocking and im not using an opteron(which would warrant getting something faster than 3500perhaps incase it started overclocking to a ridiculous speed)
     
  19. man_from_uncle

    Wise Guy

    Joined: 9 Jan 2006

    Posts: 1,345

    Actually Peetee a good combination of FSB and timings is good for any overclock, even a really big one. Any half decent overclocking motherboard will have enough divider options to allow you to reach your maximum overclock regardless of ram frequency. The only limiting factor on reaching the chips limit will be temperatures, voltages and motherboard HHT limits (or CPU mulipliers depending on which way you look at it). As long as those limits are high you can reach your maximum ghz overclock regardless of what ram you are using.

    However the difference between 2.7ghz with a loose timings and a low memory speed and 2.7ghz with tight timings and a high speed is quite a lot (maybe up to even 20%). Therefore the best ram for any overclock will always be the one with the best sweet spot. So far I don't think anyone has absolutely worked out how to determine what the best sweet spot is (except through trial and error), but in my opinion the low frequency-low latency ram has better sweet spots than the high frequency-high latency ram.
     
  20. peetee

    Soldato

    Joined: 18 Aug 2004

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    hmm, well iv got a shuttle sn95g5v2, its hardly an overclocking motherboard is it, iv got a newcastle core 3500 and 2x512 pc3200 geil value ram, i tried lowering timings and upping fsb slightly but i dont actually think its done it.. cpuz says for 166 its the lower timings but for 200 its the normal ones, whats your opinion?