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Front Side Bus Questions

By iCE · 17 replies
Nov 19, 2002
  1. I am currently designing a new system for myslef and I am a little confused about the FSB. Since an AMD Athlon XP 2600+ uses a FSB of 266 MHz, would running 400 MHz DDR RAM with this CPU (on an ASUS A7V8X) be a waste of money if I don't plan on overclocking the FSB? I believe this creates a bottleneck and if you aren’t going to overclock the FSB you are better off with 266 MHz DDR RAM - am I correct? :confused:
  2. conradguerrero

    conradguerrero TS Rookie Posts: 310

    I don't think you can overclock the fsb.
  3. Arris

    Arris TS Evangelist Posts: 4,686   +350

    You would be better going with the 333fsb version of the 2600+ which is now available and pairing it with some PC2700 (333 DDR) memory. A lot of motherboards are now allowing the memory and CPU to run synchronously so that you get a performance gain. 400 DDR has not been proven to provide a performance increase over 333 DDR. Your best bet for a new Athlon system would be nForce2 board with Dual Channel DDR and 333 fsb support for newer XP CPUs. And most boards also now support fsb adjustment, the only problem is that sometimes the dividers used to calculate the clock speeds for the AGP and PCI don't support higher fsb values or separate clocks, so when you overclock the fsb, the AGP and PCI clocks get overclocked too.
    And no, there isn't much point to having faster memory as the fsb would cause a bottleneck between the memory and the cpu.

    I'm currently running an 2100+ @ 140fsb which results in a faster CPU clock (2200+ speed 1820Mhz) and also a gain in performance due to the rest of the memory subsystem also being slightly overclocked by this.
  4. Th3M1ghtyD8

    Th3M1ghtyD8 TechSpot Paladin Posts: 664

    Some motherboards support separate memory and FSB settings, i.e. asynchronous operation, so memory accesses are slightly faster for example for DMA devices (which transfer to memory without CPU intervention), but the FSB will still limit performance of memory to some degree.
  5. Arris

    Arris TS Evangelist Posts: 4,686   +350

    Well pointed out. Still the 400 DDR isn't worth it. Still better off opting for the 333 fsb Athlon 2600+ and getting 333 DDR memory and running it synchronously. Would you agree Th3M1ghtyD8?
  6. SilentNoise

    SilentNoise TS Rookie Posts: 22

    On most chipsets, running the memory at 200 ( 400mhz or PC3200 ) will result in less aggressive memory timings so you don't really get much performance above PC2700 even if the cpu has a fast enough FSB.
  7. Rick

    Rick TechSpot Staff Posts: 4,572   +65

    400Mhz DDR might not be a total waste of money, because when it comes time to upgrade, you can still hold on to your memory. CPUs are probably turning to 333Mhz as a new standard, so PC2100 and 1600 are quickly becoming outdated.

    But yes, you will not see the performance increase in terms of bandwidth. It may be more possible overclock this memory though and also set it to lower latency settings than slower memory. This could result in a reasonable performance boost.
  8. Didou

    Didou Bowtie extraordinair! Posts: 4,274

    It doesn't seem like PC3200 will ever have a JEDEC ratified standard so I think companies are waiting for DDR-2 for 200+ mhz speeds.

    It's always a good idea to get the fastest out there, but I wouldn't touch PC3200 DDR-1 modules with a 10 foot pole.;)

    Dual DDR at PC2700 on the other hand.:cool:
  9. iCE

    iCE TS Rookie Topic Starter Posts: 25

    I didn't even know there was a 333 MHz FSB version of the Athlon XP 2600+. I thought the first 333MHz FSB Athlon XP was the Athlon XP 2800+?!
  10. Arris

    Arris TS Evangelist Posts: 4,686   +350

    UK Online store with 2600+ 333fsb for sale

    But they might have gotten it wrong since on the AMD site they only seem to list 2700+ and 2800+ with 333fsb. In that case you would be better putting the extra cash from buying 400 DDR to the processor and getting a 2700+ and 333 DDR ram.
  11. Th3M1ghtyD8

    Th3M1ghtyD8 TechSpot Paladin Posts: 664

    I heard there was going to be a 2600+ with a 333Mhz Bus as well, as a lower-end 333 chip. There is another thing that I have noticed, retailers stating incorrect actual clock speeds for 2400+ and 2600+s, stating 2.0Ghz instead of 2.06 for the 2400 and 2.06 instead of 2.13 for the 2600.

    I would buy the 333Mhz RAM even if you only get a 266Mhz Bus chip, that way you also have the option of unlocking your processor, lowering the multiplier and running it on a faster bus, for the same speed. (Assuming your board supports this).
    This was my original intention with my new rig, I have 2x 2400+ (266Bus) and some 333Mhz, but so far I am still very impressed with my rig and have no need to overclock it yet.

    If you get a 333Mhz Bus Chip then I would recommend getting some Decent branded 333 or even some 400+ Mhz RAM, just so that you could run the 400Mhz@333 but at a lower CAS setting, and so boost performance. As for buying 400 RAM just for future proofing, forget it, DDR-II will be out soon for PCs I expect and that will be clocked at 1Ghz+, so 400 will be well obsolete.

    Dual Channel DDR is well worth the money from what I've heard if you have a mobo that supports it.
  12. Didou

    Didou Bowtie extraordinair! Posts: 4,274

    Well, now that a 200mhz ( 400 ) FSB has been announced for the Barton, the plot thickens.;)

    So far, the nForce2 platform is the only one validated to run the 200 FSB Barton.

    It is also rumored that the kt400a will have dual channel DDR. Whether or not it has better performance then the nForce2 platform remains to be seen, & there are also no known release dates for it.

    On another note, a 200mhz FSB for an AthlonXp would be able to adress 3.2GB/s so wouldn't a Dual Channel PC2100 ( 2.1 GB/s ) be sufficient to saturate it ?
  13. Didou

    Didou Bowtie extraordinair! Posts: 4,274


    Here's an article where they test a 166mhz ( 333 -> 2.7 GB/s ) FSB AthlonXP & run the Dual Channel memory at 133mhz, 166mhz & 200mhz thus achieving 4.2 GB/s, 5.4 GB/s & 6.4 GB/s.

    Even though the 4.2 GB/s provided by Dual Channel PC2100 is much higher then the Athlon's 2.7 GB/s, there is still a noticeable performance loss.

    Looking at these figures, I can't help but think that Dual Channel DDR platforms aren't very mature yet. Even the Granite bay is far from achieving the 4.2 GB/s that 2.PC2100 is capable of ( in theory ) & that's with the P4 FSB at 133 ( 533 -> 4.2 GB/s ).
  14. Arris

    Arris TS Evangelist Posts: 4,686   +350

    Just to let you know Didou ;)
  15. Didou

    Didou Bowtie extraordinair! Posts: 4,274

    15% more is always a good thing but it's not reaching the maximum theorical potential. I want more, more, MORE !!!:evil:

    OK, I'm getting palpitations now. I think I better lie down.:dead:
  16. Didou

    Didou Bowtie extraordinair! Posts: 4,274

    X-Bit has confirmed that the KT400a will be a Single-channel DDR solution. DDR 400 should be supported as well as 166 FSB. No word on the 200 FSB that AMD is considering for the Barton during 2003.

    Does this remind anyone of the KT266 / KT266a era ? ;)
  17. Arris

    Arris TS Evangelist Posts: 4,686   +350

    Can I borrow that Ten foot Pole from you Didou so I can touch the OCZ PC3500 ram that I just received ;)

    I'm planning on getting as much of an overclock as possible so the ram which has been tested at 434Mhz DDR should give me a big enough leeway memory wise.
  18. nebulus

    nebulus TS Rookie Posts: 32

    DDR400 might not be a very wise choice for his board (A7V 8X) in terms of upgrading, unless you want to be limited to the maximum chip of 1 Ghz (that is if you can actually afford the very expensive 1GB Chip of DDR400). This is because the motherboard in question has the snag of only being able to support up to 1Ghz DDR400 in one of its 3 DIMM Slots. It supports 2 Sticks of DDR333 up to 2Ghz, and all three DIMMS in the lower Clock Speed Modules up to 3Ghz.

    I have the same board and have settled on using PC2700/DDR333 option, but im sure this arrangement of being only limited to the two slots will be a hinderence for me in the future (unless i upgrade my board).
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