The athlon DDR issue...

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Thread: The athlon DDR issue...

  1. #1
    Reef Shark
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    Post The athlon DDR issue...

    The athlon are currently running 100MHz at DDR (200MHz EV6 bus)... And the big hype currently is the transition to the 266MHz EV6 Bus... Requiering new EXPENSIVE (at launch) memory modules...

    Pc100 memory worked well in the Athlon at 200MHz in DDR.. Then why won't the pc133 work at 266??

    Some sick joke or just a way to bleed people of there well earned money??
    (Already got 256 meg of cas2 SDRAM.)

    Answers please!

  2. #2
    Reef Shark ilsie's Avatar
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    Originally posted by ClawViper:
    The athlon are currently running 100MHz at DDR (200MHz EV6 bus)... And the big hype currently is the transition to the 266MHz EV6 Bus... Requiering new EXPENSIVE (at launch) memory modules...

    Pc100 memory worked well in the Athlon at 200MHz in DDR.. Then why won't the pc133 work at 266??

    Some sick joke or just a way to bleed people of there well earned money??
    (Already got 256 meg of cas2 SDRAM.)

    Answers please!
    The way DDR works is by transmitting data on both clock edges. PC100 doesent do that- so it's actually running at only 100MHz. Similarly, they had to design a system, that while based off the same architecture, transfers on both clock edges. It requires different operating voltages, etc., and also does something called a split transaction. This essentially takes the two edge signals and combines/ separates them.

    If you look at anandtech's weekly memory price guide (and probably the one on this site, I havent looked at it) you will see that DDR ram really isnt that expensive.
    2x AMD Athlon-MP 1900+'s
    2x Thermalright AX-7's w/Panaflo-L's
    Tyan Tiger-MPX
    1024MB buffered Samsung PC-2100 DDR
    eVGA GeForce4 Ti4400
    SB Live Platinum 5.1
    Adaptec 29160 SCSI adapter
    Maxtor Atlas 10k 18.4 gig SCSI-160
    Seagate Barracuda III 40 gig ATA-100
    Seagate Barracuda IV 80 gig ATA-100

  3. #3
    Hammerhead Shark
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    Originally posted by ClawViper:
    The athlon are currently running 100MHz at DDR (200MHz EV6 bus)... And the big hype currently is the transition to the 266MHz EV6 Bus... Requiering new EXPENSIVE (at launch) memory modules...

    Pc100 memory worked well in the Athlon at 200MHz in DDR.. Then why won't the pc133 work at 266??

    Some sick joke or just a way to bleed people of there well earned money??
    (Already got 256 meg of cas2 SDRAM.)

    Answers please!
    Because the memory bus is still running at 100MHz on the 200MHz boards. 200MHz is the main system bus, not the memory bus.

    Edit: Also, the new DDR board are only going to run a 133MHz memory bus, it's just going to be double-pumped (to use Intel's termonology)

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    [This message has been edited by Sketch (edited December 01, 2000).]
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  4. #4
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    Ok... Unless i'm misstaken DDR is using both the rise and fall edge of the of the memory bus. The Athlon does this right now with SDRAM..

    Of course the DDR system has to use diffrent methods to reach the 200MHz.. But what i ask is that does this need new designed memory?
    Is the 200MHz DDR so diffrent from the 266MHz DDR?

    REPLY TO: Sketch
    If theres only 100MHz to the memory... Then whats the 200MHz system bus comunicating to??
    The AGP, ISA, IDE, PCI or what? )

    REPLY TO: ilsie
    "two edge signals and combines/ separates them." Fake DDR? If they could fake 100 to 200 then how hard could it be to fake 133 to 266??


  5. #5
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    Now look.. I'm not against new technology...

    It's just that why would i pay an arm and a leg for pure DDR266?? Or DDR2100 as they want to call it.. When they could do DDR200 whith the standard PC100??


    It seems the pc industry is like chasings rabbits... No matter how fast you run, they will always be faster... And you end up paying the price..


  6. #6
    Mako Shark
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    Originally posted by ClawViper:
    Now look.. I'm not against new technology...

    It's just that why would i pay an arm and a leg for pure DDR266?? Or DDR2100 as they want to call it.. When they could do DDR200 whith the standard PC100??

    It seems the pc industry is like chasings rabbits... No matter how fast you run, they will always be faster... And you end up paying the price..
    I think you misunderstand how the processor communicates with memory. In order to get to memory, the processor much go through the chipset. Think of the chipset as a black box... you don't know exactly how it works, but it happens to do what you want it to do.

    You should consider that the chipset sends and receives data from memory and the processor separately. There are buffers that lie in between, and data sometimes sits in those buffers until either the processor or memory is ready to use it.

    On an Athlon system, the processor to chipset bus runs at 200MHz. This is a double-pumped 100MHz bus, but all transactions actually run at double speed.

    The chipset to memory bus runs at 100MHz or 133MHz on SDR systems. On DDR systems, the memory speed must match the processor speed, so you will need 266Mhz Athlons to use PC2100 memory (which don't exist yet). PC2100 memory is actually 133MHz. Data, however, can be processed on both edges of the clock, so data can go twice as fast.

    The main point you should realize is that data gets processed by the chipset, which is a complicated piece of logic that sits between the processor and memory. The processor never directly accesses memory. It only accesses the chipset, which in turn will forward requests to the memory according to its logic.

    Hope that helps... sorry it's kind of a complicated topic, but hopefully you understood.

  7. #7
    Reef Shark Marsolin's Avatar
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    Originally posted by ClawViper:
    Now look.. I'm not against new technology...

    It's just that why would i pay an arm and a leg for pure DDR266?? Or DDR2100 as they want to call it.. When they could do DDR200 whith the standard PC100??


    It seems the pc industry is like chasings rabbits... No matter how fast you run, they will always be faster... And you end up paying the price..

    Another note that may be of interest. PC100 and PC133 DIMMs are not pin compatible with DDR. They only have 168 pins and have two keys (notches). DDR has 184 pins and only one key.

    One reason for the additional pins stems from the clocks. SDR SDRAM uses what's known as common clocking. DDR SDRAM uses source synchronous differential clocking. Diffential cloocking has better signal quality, but it also means each clock is actually 2 clocks instead of one. Each clock is 180 degrees out of phase.

    Because of this there is now way to make current memory compatible with DDR systems.


  8. #8
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    Your front side bus is 100MHz but its double pumped (DDR) to make it effectivly 200MHz. The plain fact is it is still 100MHz, but because it is DDR it is "simulating" a 200MHz FSB. That is why PC100 memory works with Athlon's 100MHz FSB DDR = 200MHz FSB because in actuality your FSB is 100MHz and so is your memory.

    This rule also applies to memory. DDR SDRAM is also double pumped to make it simulate a data transfer at 266MHz for example. But it is really running at 133MHz. In order to do this though you need a new system that will comply to DDR standards and thus the 184pin DDR SDRAM, the new memory. Your current memory is SDR so 100MHz = 100MHz plain and simple.

    To answer your original post, PC133 memory wont work with the new 266MHz bus because they designed it to work with DDR SDRAM. Not SDR SDRAM two compeletely different kinds of memory, DDR SDRAM being the newer and giving you double the performance. Now ask yourself this question:

    If you were AMD, why would you hold back the true potential of your 266MHz EV6 Bus with older PC133 SDR SDRAM if there is DDR SDRAM that will theoretically give you double the performance?

    They could probabaly give us 266MHz EV6 MB that support older SDR SDRAM, and maybe they will, but considering the small price difference between SDR SDRAM and DDR SDRAM, I dont blame them for pushing the new technology. One thing is for certain though, DDR SDRAM kicks RDRAM a@#!
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    You should know that the Ali chipset allows for the use of SDRAM and DDRAM (but the mobo must impliment this capability). I don't know about the 760 chipset. The Ali should perform pretty good (maybe a little slower than the 760 (3-percent?)- maybe equal), they have a better record WRT memory transfer rate v.s VIA. I'm not optimistic about the quality of VIA's DDR chipset - hopefully VIA will surprise me.

  10. #10
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    KT133 chipsets using PC100/133 SDRAM communicate asynchronously!

    with DDR SDRAM, that's no longer possible.
    133DDR MHz Front Side Bus are necessary to take advantage of 133DDR memory, otherwise u would create a bottleneck in the chipset.

    besides, there is a DDR100 brand of memory (PC1600) which is able to use CPUs with today's FSB of 100DDR, so u only need 133DDR FSB for the faster PC2100 brand.

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  11. #11
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    Originally posted by ClawViper:
    Ok... Unless i'm misstaken DDR is using both the rise and fall edge of the of the memory bus. The Athlon does this right now with SDRAM..

    Of course the DDR system has to use diffrent methods to reach the 200MHz.. But what i ask is that does this need new designed memory?
    Is the 200MHz DDR so diffrent from the 266MHz DDR?

    REPLY TO: Sketch
    If theres only 100MHz to the memory... Then whats the 200MHz system bus comunicating to??
    The AGP, ISA, IDE, PCI or what? )

    REPLY TO: ilsie
    "two edge signals and combines/ separates them." Fake DDR? If they could fake 100 to 200 then how hard could it be to fake 133 to 266??

    To reiterate what Arcadian said, the memory talks to the chipset at 100 MHz (or 133) and the chipset sends that to the processor, and the fact that the chipset and processor talk at twice the speed of the memory, that means that it can send stuff from the PCI, ISA, USB, and other busses at the same time as the memory, using the same bus. DDR means that during memory transfers, it's going to use the entire FSB for memory transfers.

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  12. #12
    Reef Shark Marsolin's Avatar
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    Originally posted by gaffo:
    You should know that the Ali chipset allows for the use of SDRAM and DDRAM (but the mobo must impliment this capability). I don't know about the 760 chipset. The Ali should perform pretty good (maybe a little slower than the 760 (3-percent?)- maybe equal), they have a better record WRT memory transfer rate v.s VIA. I'm not optimistic about the quality of VIA's DDR chipset - hopefully VIA will surprise me.
    I've heard that the 760 also supports both types of memory.

  13. #13
    Sushi
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    Originally posted by ClawViper:
    The athlon are currently running 100MHz at DDR (200MHz EV6 bus)... And the big hype currently is the transition to the 266MHz EV6 Bus... Requiering new EXPENSIVE (at launch) memory modules...

    Pc100 memory worked well in the Athlon at 200MHz in DDR.. Then why won't the pc133 work at 266??

    Some sick joke or just a way to bleed people of there well earned money??
    (Already got 256 meg of cas2 SDRAM.)

    Answers please!

  14. #14
    Great White Shark Moridin's Avatar
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    Originally posted by ClawViper:
    The athlon are currently running 100MHz at DDR (200MHz EV6 bus)... And the big hype currently is the transition to the 266MHz EV6 Bus... Requiering new EXPENSIVE (at launch) memory modules...

    Pc100 memory worked well in the Athlon at 200MHz in DDR.. Then why won't the pc133 work at 266??

    Some sick joke or just a way to bleed people of there well earned money??
    (Already got 256 meg of cas2 SDRAM.)

    Answers please!
    Others have already touched on much of this, but I will try to explain anyway. The CPU doesn’t communicate with any of the buses (memory, PCI, AGP) in a system directly, instead it communicates with the chipset which routes data to the appropriate location.

    When data goes to the CPU from memory or from memory to the CPU it always goes through the chipset. Up until the 760 chipset all Athlon systems had an unbalanced setup. That is, they had more bandwidth between the chipset and CPU then the chipset and memory. The Athlon bus was 100 MHz DDR (100 *2*8=1600MB/sec) while the memory was 133 MHz (or 100 MHz) (133*8=1066MB/sec). This meant that although the Athlon FSB could communicate at 1600MB/sec, the CPU never communicated with memory faster then 1066MB/sec.

    The different clock speeds of the two busses also introduced another problem. There can't be any fixed relationship between the time data arrives at the chipset from memory and the time it is sent to the CPU. In other words the chipset must operate asynchronously. If you want to transfer data from the memory bus to the CPU bus you have to hold it in the chipset for one clock cycle. This increases the memory latency.

    I understand the 760 is a synchronous chipset. This means that the CPU bus and the memory bus use the same clock (sort of). This allows it to eliminate the one cycle latency penalty for asynchronous operation but it means that you can no longer have the FSB and memory bus operating at different speeds. If you want to use PC2100 memory (133 MHz DDR) you need to have a 133 MHz DDR FSB (or something equivalent)

    I think VIA is producing an asynchronous DDR chipset. That means you could mix FSB speeds and memory speeds but you would have a performance penalty due to the additional latency.

    You would not get much extra performance from a 133 MHz DDR FSB if you were only using PC 1600 memory. In fact it would likely have lower performance then a synchronous chipset using a 133 MHz DDR FSB and PC 1600 memory.

    You could also have 133 MHz DDR FSB with PC133 Ram, but it would not perform anywhere near as well as the 760 with a 100 MHz DDR FSB and PC1600 memory. In most cases there is almost no point in using a faster FSB on the Athlon without speeding up the memory.

    I hope this is the information you were looking for and that I have presented it in a clear way.

  15. #15
    Hammerhead Shark
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    looks like the ali chipset is better than i hoped - fast - link at jc's site. www.jc-com/pc

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