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Real bus speeds of Via 266 chipset and DDR

Discussion in 'AMD Overclocking' started by Jon D, Jul 27, 2005.

  1. Jon D

    Jon D Guest

    I'm posting to get some advice about REAL bus speeds.

    I want to know how much my chipset and processor would benefit from
    different memory. The trouble is that I have become confused by
    "effective bus speed" and "actual bus speed" and "nominal bus speed"
    and so on.

    As you may be tired of hearing (!) I am running a Duron Applebred
    1800 in a Via 266 mobo made by Syntax with 768 KB of 133 SD-RAM. The
    BIOS is by Phoenix. The CPU temp under load is ok at 44 degrees C.

    The manual for the mobo is available at http://tinyurl.com/9rc5d

    My Syntax mobo can run either SD-RAM or DDR. I am thinking that I
    could upgrade the 768MB of 133 SD-RAM to DDR in order to get an
    increase in performnce.

    Then later on this year, I can build a faster PC using all new parts
    except for the DDR which I could take from the existing Snytax mobo.
    (I would put the slower SD-RAM back into the Syntax mobo to create a
    basic PC.) I do not want to spend more money than I have to as I am
    on a budget.

    QUESTION ONE. What speed DIMM memory would work well with my
    Via266/Duron1800 and yet still be good to use with a faster processor
    later this year which will probably be a mid-power socket 939 (and
    some mobo chipset which I haven't decided on yet)? Is PC2700 too

    QUESTION TWO. How fast does the bus on my mobo/cpu actually run
    these devices at:

    (a) the "133/266 MHz FSB" on the cpu
    (b) the bus on 133 MHz SD-RAM
    (c) suitable DDR in Q.1 (PC2700 ??)
    (d) the PCI bus.

    Thank you guys.
    Jon D, Jul 27, 2005
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  2. Jon D

    Alex Fraser Guest

    I don't know what you mean by "nominal" bus speed, but "actual" and
    "effective" are quite straightforward. The "actual" bus speed is simply the
    frequency of the bus clock signal, and the "effective" bus speed is that
    frequency multiplied by the (peak) number of data transfers per clock cycle.
    The logic here is that since a traditional bus can make only one transfer
    per clock cycle, a bus that can make two transfers per clock cycle (that is,
    a Double Data Rate or DDR bus) has the same peak transfer rate as a
    traditional bus operating at twice the frequency.
    I think the increase will be modest (perhaps up to 10% - not normally
    noticeable), but I don't have any figures to hand.
    PC2700 may be usable but if so will limit performance on faster processors;
    it would be better to go for PC3200.
    I'm not sure what you are asking here. The FSB, memory bus and PCI bus are
    all separate. Usually the clock signals for each are derived (via
    dividers/multipliers) from a common source, so it's not strictly true to say
    they are independent.

    Alex Fraser, Jul 27, 2005
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  3. Jon D

    GT Guest

    QUESTION ONE. What speed DIMM memory would work well with my
    Simply for explanation purposes I would add that PC2700 is another name for
    DDR333 and PC3200 is another name for DDR400.
    DDR stands for Double Data Rate, so does 2 transfers per clock tick so...
    DDR333 is guaranteed to be stable on bus frequencies up to 166.666MHz and
    DDR400 can run on buses up to 200MHz. DDR400 memory (200MHz) can be used at
    slower frequencies - the rating is its maximum stable speed.
    GT, Jul 27, 2005
  4. Jon D

    Cuzman Guest

    Jon D wrote:

    " QUESTION ONE. What speed DIMM memory would work well with my
    Via266/Duron1800 and yet still be good to use with a faster processor
    later this year which will probably be a mid-power socket 939 (and some
    mobo chipset which I haven't decided on yet)? Is PC2700 too slow? "

    You need PC3200 for any socket 939 CPU.

    " QUESTION TWO. How fast does the bus on my mobo/cpu actually run
    these devices at:
    (a) the "133/266 MHz FSB" on the cpu
    (b) the bus on 133 MHz SD-RAM
    (c) suitable DDR in Q.1 (PC2700 ??)
    (d) the PCI bus. "

    These two articles explain all the relevant frequencies:

    The FSB of your CPU, chipset and SDRAM is 133.33r MHz. PC2100 DDR SDRAM
    has the same bus rate as PC133 SDRAM, but is called DDR266 because it
    can transfer data on both the rising and falling edge of the clock
    cycle. It doesn't actually double the effective bus rate of 133.33r
    MHz, and the claims of it operating at 266.66r MHz are arguably just
    marketing speak.

    The PCI and AGP bus work on dividers of the motherboard chipset bus.
    When operating a chipset bus of 133.33r MHz, your PCI bus will work on a
    divider of 1/4, equalling 33.33r MHz. Your chipset bus can also operate
    at 100 MHz with slower processors, from which the PCI bus will operate
    on a divider of 1/3, also equalling 33.33r MHz. Your motherboard's AGP
    bus can operate at AGP4x, four times the speed of the PCI bus, thus
    equalling the chipset bus of 133.33r MHz.
    Cuzman, Jul 27, 2005
  5. Jon D

    Mike Walsh Guest

    PC2100 memory will run at 266 Mhz, but if you plan on using it in a newer system you should get at least pc2700, preferably faster.
    The FSB and memory bus run at 133 Mhz. With DDR the effective speed is double because there are two data transfers per clock cycle.
    PC2700 memory will run at up to 333 Mhz. It will also work with your slower bus.
    A standard PCI bus runs at 33 Mhz.
    Mike Walsh, Jul 27, 2005
  6. Jon D

    kony Guest

    Almost none except in less common apps that have very high
    memory bandwidth needs. In such cases it might be upwards
    of 20% or so but usually under 5%.

    Then just ignore ALL of those terms, as none are technically
    based and all just nonsense.

    For any bus you have 3 parameters:

    Clock generator derived frequency.
    Bus Multiplier (multiplies the clock)
    Data rate

    So for an example, given a Duron 1.8GHz you'd have a FSB
    with 133MHz clock generator, 2x bus multiplier (hence the
    term "DDR", Double Data Rate), and a data rate of (in this
    case) 2 X 133 = DDR266. It should not be called 266MHz
    because the whole purpose of the "DDR" term is to
    distinguish between clock generator rate and data rate.

    Not worthwhile.
    Youi'd get more gain by buying an nForce2 motherboard and
    slightly overclocking (or even NOT overclocking), but then
    you still need the DDR memory. KT266 chipset is simply
    slower per the same data rate, clock speeds, etc, than
    nForce2. This is ignoring the difference the memory makes
    BUT when considering the benefit of the memory one must also
    look at the rest of the bottlenecks, particularly when the
    memory isn't such a large difference.

    Howver, the biggest performance boost from a singular
    purchase would be the CPU. Again your board is a limitation
    since it only has DDR266 FSB support.

    Frankly, there's no point in upgrading that system at all
    then. You'd be better off waiting till you had the new
    motherboard/etc so you can be sure the memory works properly
    with it. I don't mean to be offensive but rather factual
    when I note that- The parts are low-end stuff, as always
    it's expected that it'll be more problematic and expensive
    to upgrade them.

    Yes, PC3200 CAS2.5 at a minimum.

    133MHz clock, DDR266

    133MHz clock, Single Data Rate 133 ( 1 X, not 2 X)
    133 clock, Double Data Rate

    The thing is, often memory isn't a major bottleneck, not as
    much as CPU, hard drive, video card, all depending on the
    33MHz. That is standard and has little to do with what
    board you choose unless you try to overclock.

    Frankly you should just put the money aside and upgrade
    everything at once, a little sooner if you're really itching
    for more performance. For many uses you might not even be
    able to perceive a difference with the DDR instead of SDR
    memory. System might feel a tiny bit snappier but it should
    easily be fast enough at typical tasks already, with the
    more demanding tasks benefitting more from a faster CPU (and
    one with more L2 cache).
    kony, Jul 27, 2005
  7. Jon D

    chris Guest

    Simply for explanation purposes I would add that PC2700 is another name
    You might also want to mention that if you use DDR400 with rating of CAS3,
    the memory will run at lower CAS when using it at DDR333 or lower. For
    instance, I have DDR400 CAS3 and is running at DDR333 CAS2.5. I'm not sure
    that this is true for all brands of memory so, the BIOS should be set to
    speed detect...to make sure you don't experience any problems.
    chris, Jul 27, 2005
  8. Jon D

    Wes Newell Guest

    See the Real Front Side Bus in link in sig line.
    Most normal people are.:)
    If buying today, you should buy the fastest reasonably priced ram. I'd say
    that's PC3200 which is rated for a 200MHz bus (DDR400). However, you can
    use ram as slow as PC2100 (133MHz DDR266) in both your current board and
    most/some A64 boards. Buying the ram today won't help your current system
    much at all. Your delima is what will ram prices be later on when you
    actually need the DDR ram. Ram is cheap now, but will it be cheaper later????
    133MHz clock. DDR266.
    133MHz clock
    133MHz clock DDR266, but don't think that will improve performance by a
    big margin. It won't. Approximately 90% of CPU data request are serviced
    by the CPU cache and the speed of the external ram has very little to do
    with it. At most I would guess you'd get a 5% overall performance increase
    over standard sdram. You also need to remember that the ram controller is
    in the chipset and all the ram data must share the FSB path to the CPU,
    which is DDR even with SDR ram.
    It should be 33MHz on any board, but it will go higher if you overclock
    the FSB and your MB doesn't have a PCI lock. And yours doesn't.
    Wes Newell, Jul 27, 2005
  9. Jon D

    Wes Newell Guest

    While PC3200 or faster would be preferred, it's certainly not a
    requirement. The system will run fine on PC2700. I'm not sure what the
    bottom limit is but PC2100 should also work, maybe. It will in my 754
    system. From the AMD product brief...

    An integrated memory controller with peak memory bandwidth of up to 6.4
    GB/sec, supporting PC3200, PC2700, PC2100, or PC1600 DDR SDRAM
    Wes Newell, Jul 27, 2005
  10. Jon D

    Wes Newell Guest

    Nope. It's actual bus clock is 133MHz (DDR266), but not 266MHz.
    Wes Newell, Jul 27, 2005
  11. Jon D

    Sleepy Guest

    I have the same board and the bus speed is 133mhz. Some sockets on the
    board run on a locked ratio of that bus speed - for example the PCI slots
    run at 33mhz or 1/4 and memory runs at 133mhz like your SDRAM does.
    Some components on that board can run at 266mhz such as the CPU
    which runs internally at double the bus speed and DDR if you install it
    will run at double the bus speed.

    If you put in PC3200/DDR400 it will only run at the stock speed of 133mhz
    (x2 is 266mhz which is the speed of PC2100/DDR266) but you could
    overclock the FSB a little if you put in that RAM - you do it in the Bios
    and if you put it up to say 140mhz your CPU would perform like a 1900
    or 2000. Every component connected to that board would run a little faster
    and of course a little hotter so make sure your case has decent cooling if
    do that.

    Your overclocking potential is limited on that board because you can only
    raise the CPU core
    voltage by up to .75v - a real overclockers board would allow about 3x that

    I went from SDRAM to DDR on this board and it made a noticeable differance -
    I never benchmarked
    it but most ppl say the differance is 10% - it just felt quicker. Going from
    512mb to 1gb made the biggest
    differance - playing any modern game (HL2, Doom3, Far Cry etc on WinXP) with
    less than 1gb and you
    are bound to get plenty of Hard Disk access and stuttering. But playing
    those games on a Duron 1800 isnt
    that great either. But Im not sure you have a Duron - theres no such chip as
    an Applebred - if you mean
    Thoroughbred then thats a Athlon XP1800 you have. Use this program to check
    http://www.cpuid.org/cpuz.php - it'll also diagnose your RAM and tell you
    its CAS speed.

    I have a XP2400 (the fastest CPU that board can support) with 1gb DDR
    running at the stock 133mhz
    like PC2100 even though its PC2700 and a Radeon 9700. I can play HL2 at
    1024x768 High settings
    and its smooth. Doom 3 I use 800x600 medium settings and Far Cry 1024
    med/high settings works great.
    I never worry about resolutions higher than 1024 since I use an old CRT
    monitor - a Sony Trinitron tube
    with flat screen that looks just fine.

    When I had just 512mb of RAM I was getting plenty of Hard Disk access during
    games that causes that
    stuttering effect and a cheap option that helped a lot was putting an old
    Hard Drive back in my system.
    I had a 120gb new drive with everything on including the pagefile. I put the
    old drive in as a slave drive
    or D - formatted it - and put the pagefile on that instead of the C drive -
    at a fixed size of 2gb.
    That way when my RAM was used up and virtual RAM was being used there were 2
    drive heads handling
    the movement of data instead of just one and that reduced the stuttering
    effect noticeably. Maybe this is an option
    you can consider?

    Hope this helps.

    Sleepy, Jul 28, 2005
  12. Jon D

    Jon D Guest

    Definitely an Applebred. See


    "The Applebred is the new revision of the Duron series from AMD. It
    is a tuned down Thoroughbred B CPU"
    Jon D, Jul 28, 2005
  13. Jon D

    Jon D Guest

    On Wed 27 Jul 2005 14:55:22, Cuzman wrote:
    Nice links. Thank you. From reading your links and also Wes
    Newell's page ("The Real FSB") I think I can see where I was just not
    getting started off on a proper understanding.

    I had seen the spec for the FSB of some AMD cpu stated in some places
    as 100 MHz (or 133 MHz or whatever) and then I had seen the specs for
    the same chip but with double the FSB value - ie 200 (or 266 or

    The single/lower value seems to be the actual clock speed of the FSb
    but the double/larger value is the Data Rate. And that term is
    nominal because, so it seems, in the original designation there was
    no reference by AMD to MHz. Other (later?) AMD documents seem to
    contain the term MHz, for example http://tinyurl.com/ytjqq

    I guess it's all a bit like the Athlon model numbers with the plus
    sign after them: the cpu does not run at that speed but was
    originally a guideline of the cpu's claimed speed when comparing
    Intel chips.

    What you say is almost the same as I just wrote exept that the AMD
    document I link to above claims the Duron's FSB is the higher/double
    rate but that is pretty misleading if SD-RAM is used which IIRC is
    all that was available for the early Duron.

    Useful. Thanks.
    Jon D, Jul 28, 2005
  14. Jon D

    Jon D Guest

    -- trimmed --

    On Wed 27 Jul 2005 21:21:36, Wes Newell wrote:
    Good article of yours. Thank you!

    -- snip --

    Wes. how do you know my mobo doesn't have a PCI lock? :) Are
    you referring to the BIOS setting "Auto Detect DIMM/PCI Clk"?

    So how do I use this setting to my advantage?

    Do I need to disable the auto detect in that setting (i.e. say no
    to that setting) and then vary the "CPU Host Clock" value?

    I am sure I have got noticeable improvements from varying the "CPU
    Host Clock" value but leave the DIMM/PCI Clock setting on AUTO.
    Could this have been possible?
    Jon D, Jul 28, 2005
  15. Jon D

    Jon D Guest

    On Thu 28 Jul 2005 09:03:51, Sleepy wrote:

    Ben/Sleepy, thank you very much for helping me further with this.
    You make some valuable points. The thing I am not so sure about is
    the query I raised with Wes in this same thread in my message:
    Maybe you know the answer to what I ask from your own experience.
    Wes observed that I didn't have a PCI Lock and I asked:

    Are you referring to the BIOS setting "Auto Detect DIMM/PCI Clk"

    If so then how do I use that setting to my advantage?

    Do I need to disable the auto detect in that setting (i.e. say no
    to that setting) and then vary the "CPU Host Clock" value?

    I'm sure I have got noticeable improvements from varying the "CPU
    Host Clock" value but leave the DIMM/PCI Clock setting on AUTO.
    Could this have been possible?
    Jon D, Jul 28, 2005
  16. Jon D

    Wes Newell Guest

    Hogwash. It's just a Tbred A or B core with the cache size set for 64k.
    Reference AMD doc Processor Model 8 Data Sheet, 25848.pdf

    Calling it Applebred or wheat bread won't change those facts. New cores
    ALWAYS have new CPUID's. Now what I heard was that the Applebred was a
    Barton core with only 64K cache enabled. So take your pick. In any case,
    it is not a new core, just a new nickname, and if you get an older Tbred A
    core, you won't be able to overclock it much either.
    Wes Newell, Jul 28, 2005
  17. Jon D

    kony Guest

    Not having a PCI lock merely means that if you choose to
    overclock by raising the FSB, the resulting PCI bus speed
    will be divided by 4. For example, if you manually set your
    board to use 155MHz FSB (if the bios even allows that), then
    the resulting PCI bus speed would be: 155/4 = 38.75MHz.
    That's usually too high a PCI bus speed and would be

    No that setting has no effect on the (lack of) PCI lock.
    Instead it causes the board to read and use the memory SPD
    programmed values on your memory modules, then use
    bios-contained logic to automatically set the memory bus
    frequency and timings. It's meant to be an "automatic" way
    of setting the system parameters without the users needing
    to know how to set it themselves. The alternative to "auto"
    (automatic) setting is manually setting it. Do that if you
    know what the settings should be. It should be same speed
    as the FSB, and the correct memory timings that your memory
    is spec'd to be able to use. Then you would need to
    extensively test memory stability.

    It's really not worth changing all these settings, at most
    it would get you a very tiny performance increase, but also
    has the potential to make system slower if set incorrectly.
    Any kinds of changes made are a very minor impact on system
    performance compared to something as simply as switching
    from a Duron to Athlon CPU.

    Being "auto" is how you should leave it. These settings
    should not be changed unless you know they need changed,
    which you do not.

    If you were to download and run "CPU-Z", it will show you
    what your programmed memory timings are and also the
    actually-used memory timings. You can compare these to see
    if your memory is being ran at optimal timings. As far as
    oveclocking, that is a try-it-and-see scenario, you would
    have to make guesstimations about how fast the memory might
    run. It's not worth the risks on that system.

    You do not "need" to do anything if the system is running
    stabily. Test it with memtest86. You could try increasing
    the CPU host clock value but it seems (based on your
    question) that you need a more basic understanding of
    overclocking before making such changes. There are various
    tutorials on the 'net, Google search for some.

    It's possible. That doesn't mean it's true. Benchmarks
    would be needed to demonstrate the effect of any settings
    kony, Jul 28, 2005
  18. Jon D

    Sleepy Guest

    Yep - just alter the CPU Host/ PCI Clock setting from 133mhz to 140mhz. Boot
    up and you should see the CPU noted as running faster in the initial boot up
    screen. Use that program I mentioned (CPU-Z) in Windows and it'll confirm
    the higher CPU and RAM speeds. With one of my sticks of RAM I managed 148mhz
    which made my XP2400 perform like an XP2600 (or maybe higher) but the other
    stick was unstable cause I couldnt run the TRAS setting low enough. If its
    unstable at 140mhz then raise the Core Voltage Regulator setting on the same
    Bios page. Use a temperature monitoring program like Via hardware Monitor or
    Motherboard Monitor and remember 40s are good - 50s are okay but if you hit
    60c forget it and run at normal speeds.
    Sleepy, Jul 28, 2005
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