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RAM for A64 939

Discussion in 'Hardware' started by Ligoman17, 9 Dec 2004.

  1. Ligoman17

    Ligoman17 New Member

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    Hey all,

    I've been on the Intel side of the fence for a couple of years now. I think enough time has passed since my bad AMD experience for me to try them again. (Last AMD cpu i bought was a K6!)

    I'm looking at building an new machine on the 939 socket and have a question on RAM. Basically, which is better for AMD, high clock or low latency? I am stuck between two choices. I can either get PC3200 with 2-2-2-6 or PC4000 with 2.5-4-4-8 timings.

    With intel you basically wanted to match your ddr frequency to your fsb, which was easy to figure. But I am not very familiar with AMD and their hypertransport bus so any input would be appreciated. So again my choice is 3200 @ 2-2-2-6 or 4000 @ 2.5-4-4-8 on a 939 A64 (1GHz HT)

    Thanks!
     
  2. Zephyr

    Zephyr Go V-Boy, Go!

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    imo, the hypertransport of AMD doesnt do very much help at all, around 50 3dmark03 marks for me...with AMD, the RAM bus speed is the same as the cpu, but you can change the ratio's. i would get the PC4000 if you're extremely into overclocking, because then you can get a decent wc system and oc your cpu to its max, without the RAM holding you back. if you arent very into overclocking, i would get the PC3200. with my HyperX, i can get 2-2-2-7 timings with a s754 setup, and my bus speed at 230. hope this helped, and didnt just confuse you more :thumb:
     
  3. TMM

    TMM Modder

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    it depends if your overclocking or not. If your not overclocking, then it would be foolish to get pc4000 ram as it would only be running at pc3200 speeds.
    pc4000 would be handy is you were overclocking, as all Athlon64 cpus (except the FX's) are multiplier locked upwards. So to increase the cpu speeds, you going to have to increase your FSB(yeah its called HTT, but im going to call it the fsb since its easier to understand ;)). Even 250fsb (read: pc4000 speeds) should be fairly easy work for a good A64 mobo, considering the memory controller is the the cpu itself!
    Im not sure how much timings affect the performance, but it should be very little. You'd rather have 250fsb at cas3 then 200fsb at cas 2.

    While im on the topic, check out memory with Samsung TCCD chips, they can do quite good fsb with lowish timings :).

    btw: you always want to run the FSB:mem at 1:1, unless you are memory limited and can't get your multiplier higher.
     
  4. Austin

    Austin Active Member

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    :thumb: TMM has summed it all up, PC3200 ideally with low latences if stock or faster rated RAM if you wish to o/c. I'd just add that lower latency is pretty beneficial for AMD64 from what I've heard/read, so you would want to keep the latency low whilst still keeping it synced with 'FSB'. You may find something inbetween such as PC3500/2700 may be of use for this. Also consider that some mobos are much more o/c'ing friendly than others, one example would be the ability to drop the 'HT multiplier' down so you could use 250x4=1000mhz instead of the 939 norm of 200x5=1000mhz, this should avoid potential problems that 5x250=1250mhz could cause.
     
  5. Ligoman17

    Ligoman17 New Member

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    So what is the "fsb" of the 939 processors? at what speed will my ram be synched to the fsb?
     
  6. Austin

    Austin Active Member

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    :cooldude: HT (like a FSB) effectively runs at 200mhz but for the true speed you factor in the HT multiplier, generally 4x200=800mhz for Skt754 and 5x200=1000mhz for Skt939. Your RAM is synced with HT pre-multiplier, hence 200mhz. 200mhz DDR is DDR400-PC3200 (200mhz with 2 signals per clock is DDR400). When you o/c for best perf you keep the RAM synced with HT so at 220mhz HT (10% CPU o/c) your RAM would need to run at DDR440-PC3500 speed ... while at 250mhz HT (25% CPU o/c) your RAM would need to run at DDR500-PC4000 speed. You can run the RAM async (eg DDR400-PC3200 @ 250mhz HT) and much like the P4 the perf hit isn't huge, but it certainly isn't ideal.
     
  7. Kameleon

    Kameleon is watching you...

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    I assume that's memory with TCCD chips (Crucial Ballistix, Corsair XL, OCZ EL rev. 3 etc) - this stuff is your best choice all around as it will do ~200 at 2-2-2 and up to 250 and further at 2.5-3-3. You can just keep relaxing the timings and getting more and more speed out of the chips without raising the voltage much. Whether you're overclocking or not, it's the best choice for RAM at the moment, unless you can still find BH-5 (and want to stick silly amounts of voltage through it)
     
  8. Ligoman17

    Ligoman17 New Member

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    Kameleon:

    Yes, the RAM i want to get is the Crucial Ballistix. They come in two flavors which I listed above. Just wasn't sure which was best for s939 but now it sounds like I should get the ddr400

    Austion:

    Thanks for the hypertransport explanation. That was exactly the information I was looking for. :thumb:
     
  9. Kameleon

    Kameleon is watching you...

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    OK, to be honest I don't know what the difference between their PC3200 and PC4000 is. The PC3200 should do 250 at 2.5-4-4, but of course that's guaranteed with the PC4000, and the PC4000 should do 200 at 2-2-2, but again that's only guaranteed with the PC3200. I'll have another look into it, but I think that's the only difference.
     
  10. JuMpErFLY

    JuMpErFLY Member

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    What he said really, I think both versions are basically the same, so the pc4000 should run at 2-2-2 timings at pc3200 speeds.

    And to go off topic, the ballistix doesn't use tccd chips
     
  11. Kameleon

    Kameleon is watching you...

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    You're right actually, whoops :blush: That'd be why it doesn't perform as well as TCCD-based memory then :p It's still excellent memory though.
     
  12. Ligoman17

    Ligoman17 New Member

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    So there is a possibility that the 4000 is the 3200 with higher clock and higher latency? Do they come from the same chips that were "binned" for either low latency or high clock speed?
     
  13. ric449

    ric449 New Member

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    As far as I know, Hypertransport doesn't even connect to memory.

    The Athlon 64's have a built in memory controller, but it still only runs at 400MHz like the last Athlon XP's. So, get PC3200 if you aren't overclocking.

    Of course, get the lowest latencies you can buy. Although, since a lot of latency is avoided over conventional systems because of the on die memory controller, they aren't as influential as they are over Intel systems.
     
  14. mrbungle

    mrbungle Undercooked chicken giver

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    depends if ur clocking really

    the 3200 looks good and theres a chance it would hit the pc4000 speeds at the crappy timings anyway so id get the 3200.

    However my ballistix pc4000 can do pc3200 speeds at 2-2-2-5 or pc4000 speeds at 2.5-2-2-5 :rock:
     
  15. Ligoman17

    Ligoman17 New Member

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    Thanks guys. Well, I'm getting closer to choosing between the two. It really sounds like their isn't much difference, but... I have watercooling and I would like to try overclocking so maybe I'll go for the 4000. Then when I am not overclocked I can run it at 3200 at tight timings hopefully. What do you guys think?
     
  16. lcdguy

    lcdguy Active Member

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    again what is stated here if your going to OC the chip get PC-4000 so you have the head room oif your not planing on OC then get the low latency. I know on my rig i got Cas 2.5 memory pc3200 and i love it.

    Corsair XMS C2 is the memory i got i would also look at the Corsair XMS LL series.
     

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