A64 Guide to Overclocking, Part I

By YellowC4S · 5 replies
Feb 4, 2006
  1. A64 Guide to Overclocking, Part I & II

    I'm not familiar with what is controllable on your particular board so I'm going to give it to you generic. You can find a lot more information on this at;

    Critical Overclocking Programs you’ll need:

    CPU-Z: General System Monitor and report.
    Memtest86: You'll need to run this from a Floppy or Bootable CD. This basic program is still considered the best for testing your RAM
    SuperPi: Intensive mathematical program that stresses CPU/Memory pretty extensively. I like this program because it gives you a good indication of your overclock in under a minute’s time.

    Critical Components for a Quality Overclock

    Power Supplies are missed so often when it comes to figure out why your system isnt overclockig the way it should. DONT SKIMP HERE! Get yourself a quality Power Supply and you'll never regret it. The Power Supply that comes with most cases is garbage. If budget is tight, Go with an ANTEC or ENERMAX case. These usually come with a pretty decent supply.

    There are several more factors that go into a quality and Stable A64 Overclock, a few of the factors we need to take into Consideration are

    CPU Multiplier
    CPU Voltage
    HTT Frequency
    HTT Multiplier
    Memory Divider (There is ALWAYS a memory Divider with a A64 system)
    Memory Voltage
    Ram Timings
    Chipset Voltage
    AGP/PCI Lock

    Finding the right combination of these settings is the only way to get the most out of your A64

    CPU Multiplier
    All A64s are at least Half Locked. This means that you can set the CPU Multiplier Lower than stock, but not Higher. This is a Good thing. Very rarely with A64's would you ever need to raise the CPU Multiplier over the Factory setting. The exception to this are the FX chips, they are fully unlocked.

    CPU Voltage
    Most A64s have a default voltage of 1.4v to 1.6V. A64s are extremely efficient and usually can only take about 1.7v before they just start producing excess heat. I've run my Mobile up to 1.9v but found it did NOT help my overclocks and simply caused the CPU to produce enormous amounts of heat. These are NOT XP-M chips! While I doubt that running voltages between 1.75 and 1.9 will cause any permanent damage, it certainly has not shown to be beneficial in any tests I’ve seen so far.

    HTT Frequency
    A64s don’t use a traditional Front system Bus. Instead they use a HyperTransport. I can only assume its abbreviated "HTT" to differentiate between Intel’s "HT" and Hyper-Threading Technology. They are VERY different.

    The HyperTransport is what controls the base frequency for communications and CPU speed in our A64 System. The CPU Speed is controlled by the HTT Multiplied by the CPU Multiplier, The HyperTransport or Memory controller is controlled by the HTT Multiplied by the HTT Multiplier, and Memory speed is controlled by the HTT Frequency, Multiplied by the CPU Multiplier and then DIVIDED by the Memory Divider. That’s a bit confusing for most folks. And it took me a while to grasp the concept as well.

    HTT Multiplier
    Most AMD Motherboards are designed to handle an 800-1000 MHz Hyper Transport bus. Factory Default on 754 CPUs is 800 MHz (A 4X Multiplier) and 1Ghz (5x) on 939 CPU's this is a Critical part of Overclocking an A64 to the Max. Pushing the HyperTransport past 1Ghz can cause all kinds of system instability that is commonly misconceived as "I maxed out my CPU" or "My Ram is holding me back"

    Memory Divider
    This is one of the most Confusing aspects of A64 Overclocking. There is ALWAYS a memory divider. Setting the Memory to 1:1 means that the HTT bus is multiplied by the CPU Multiplier and then Divided by the CPU Multiplier to set the Memory speed. This means that it is OK to run your Memory at its peak efficiency and still go higher with your HTT bus if your CPU can take it. Take note that I said its "OK" not advisable. There are still sufficient tests out there showing that running a 1:1 ratio will garner you the best overall performance. I plan on adding a few test results in the next week or so showing the difference in performance using a higher memory divider than CPU Multiplier.

    Since A64's use an On chip memory controller, the Ratio must be calculated a bit differently than old. 5:6 is NOT always 5:6.

    Memory Voltage
    Most motherboards offer a degree of memory voltage options. The memory of choice lately has been Samsung TCCD Based modules with Brainpower PCB's. These Modules run at 2.6v stock voltage, and can usually do no better with voltage up to about 2.8-2.9 volts. There have been a few reports of better settings with voltages over 3v, but these seem to be pretty rare

    Most other memory can benefit from having additional voltage run through it. The king of this is the elusive Winbond BH-5 based memory modules. If you’re lucky enough to have some of these, you may want to invest in an OCZ Memory Voltage Booster if your motherboard is compatible as these can run some very impressive timings with a lot of voltage....
    Speaking of Timings...

    Memory Timings
    There are 5 Numbers in our Timings that we need to worry about a lot. Personally, I would like to learn more about the other numbers, but as of this writing, I'm pretty much in the dark there.

    What we do need to worry about are CAS Latency, RAS to CAS Delay, RAS Precharge, and Cycle Time(Tras), and CPC (command Per Clock)
    Ideally, we want these timings to be 2-2-2-5 1T. Most TCCD based module does this at 200 MHz (DDR400) and can usually go up to 215-220 with a Bump in Voltage to 2.7, and then we need to loosen them to go higher. 2.5-3-3-7 is still considered reasonable memory timings for an A64 system, and some people even go out to 3-4-4-8, but I would personally advise against using timings that high with an A64 System. We ALWAYS want to use CPC (1T) this means the Command per Clock interface is enabled. 2T performs extremely poorly on A64 systems. But since our memory controller is on the CPU, the Double Sided memory problem that plagues XP Motherboards is not evident. Give AMD a WOOT for that one.....

    Chipset Voltage
    Usually just a small bump in Chipset Voltage will stabilize a flakey HTT bus. 1.6 is Stock on most motherboards, but 1.7 to 1.8 is acceptable as long as you have decent cooling on your Northbridge chip. Many A64 Motherboards use Passive heatsinks on these chips so before you install your dandy new A64 system, take off your NB Cooler and replace the Factory thermal past with some AS-5. This is usually enough to keep the MB Cool enough to run the extra voltage. Placing Ram Sinks on your Southbridge and any other heat producing chip is never a bad idea either.

    AGP/PCI Lock

    The AGP and PCI Bus' are tied together on all motherboards that I know of. They are also derived from the FSB (Or HTT in the case of AMD) frequency by a divider. NVidia NForce chipsets have whats called a PCI/AGP Lock. This keeps your PCI and AGP Bus at a constant speed no matter what your HTT bus is. This is CRITICAL. If y our PCI bus is too fast, you WILL corrupt hard drive data. If your AGP Bus is too fast, you WILL have Video problems. Via Chipsts have been known to have Faulty PCI locks. This appears to be corrected in the KT800 Pro Chipset, but KT800 and below SHOW a PCI Lock in most bios's but it doesnt do much... This is a Primary reason why overclockers stay away from these boards.

    On your Nforce or Via KT800Pro board you want this setting at 33Mhz if its listed as a PCI lock, or 66-67Mhz if its listed as a AGP Lock. Pushing this offers absolutely no benefit as the bandwidth provided by these frequencies is more than todays Hard Drives or AGP Video cards can use.

    Disable this. This is a feature that will automatically UNDERCLOCK your system if it feels it doesnt need to run so fast.... WHo are "They" to tell us how fast out CPU should run?

    Now.... What do we do with all this Information??? Start Overclocking of course.....

    First Thing First... Let’s see how fast our Processor can go.

    Set your Memory Divider at its lowest setting. (Usually 100 or 133) This will give us a LOT of headroom to push out CPU.

    Next, Drop your HTT Multiplier to 3x and your CPU Multiplier 1 Notch (If you have a 2 GHz CPU, drop your Multiplier down to 9x)

    With these settings most AMD systems will boot and run at a 230HTT so go there first. Once you get into Windows, Run a 1Million run of SuperPi, and then a Prim95 Max heat test for about 10 Minutes. If it passes both of those, its time to go further.
    Go 5 MHz at a Time and Repeat. During this we'll want to raise the VCore of our Processor to maintain stability. Once SuperPi and/or Prime95 fail, raise your VCore .05 Volts and Try again. SEE CPU Voltages Ademdum at the end of this guide for processor specific Voltage recomendations.
    This is a Slow Time Consuming process, so have a few Mountain Dews and some chocolate bars handy.

    Once your push your HTT bus back over 800 MHz (267HTT Bus) raise your Chipset Voltage up to 1.7

    with any luck, you'll hit 260-280HTT Depending on your CPU.

    Write this info down and then we move on to testing out Memory.
    As stated above, A64s are VERY efficient, there have been reports of outrageous overclocks using the stock AMD Heatsink. But I would still recommend a high quality Swiftech or Thermalright Unit. (Dee DavidHammocks HSF Guide for specifics)

    Anyway, Standard Desktop chips should be kept under 55c in ALL cases. It should NOT be hard to keep then under 45-48c with good quality cooling. Running higher than that is a good indication that you have misapplied your HSF and/or AS-5 Remount.
    Mobile chips are rated a bit higher, but there is still no reason to ever see temps higher than 55c. The lack of an IHS provides better contact with the Heatsink and it’s very possible to keep temps at 45 and lower with quality cooling. Even with high overclocks.
  2. YellowC4S

    YellowC4S TS Rookie Topic Starter Posts: 107

    Part II

    Torture your Memory Next
    Memory is usually the Culprit in holding back overclocks. Finding out the capabilities of what our memory can do is critical.

    Drop your HTT bus back down to 200, and reset your Memory Divider to 1:1 (Usually "AUTO") Leave your CPU Multiplier at 9x (For a 10 Stock Multi) and let start out at 215 at Stock Timings, Bump VDimm up to 2.7v(Or +.1Volt)

    The 2 tests you want to do here are SuperPi 1 Million and Memtest86 You'll need a Floppy disc or Bootable CD to run Memtest86 (Or if you have a DFI UT, there is a Modded BIOS available with Memtest built in)

    Run 5 Passes of Memtest86, then boot into Windows and Run SuperPi. You won’t be fast, but SuperPi 1Million runs a LOT of numbers through your Memory. If all goes well, go up 5 MHz at a time until one starts to error.
    That’s where we need to start loosening the timings.
    Go up .5 on Cast Latency, 1 on RAS to CAS Delay, 1 on RAS Precharge, and 2 on Cycle Time (Tras) and Repeat these tests. Depending on your memory,
    you may want to loosen them more, but I would suggest keeping them under 3-4-4-11 if at all possible. If you’re using Memory Other than TCCD based, don’t be afraid to bump your Memory voltage more. Most modules will take 2.9-3.0 Volts just fine and BH-5 has been known to go as high as 3.3 to 3.5v!

    Once you've found your Memory’s max speed, this is where we need to do some math. Most likely there’s a sizeable gap between what your CPU can do and what your Memory can do. That’s OK.... That’s why we went down a Notch or 2 on our CPU Multiplier testing.

    Lets say your CPU went to 260 Stable with a 1x drop in your Multi, Not bad.... a 340Mhz O/C on a stock 2Ghz chip... but your memory only went to 230 before you had to go to slow in your Timings. That’s OK.... Drop the HTT down to 230 and bring your Multiplier back to stock speed (10 xs in our example) you should have a Rock Solid 300Mhz overclock on your hands.

    If the Gap between your Memory and CPU is so high, you can’t get to your Max CPU Speed with your Stock Multiplier, we may need to run a higher Divider on our Memory.
    If we're talking 30+ MHz base difference.... You should probably drop your Memory Divider down to 166 and use your Max CPU Speed we figured out. Less than 30 MHz and you'll probably get better performance running 1:1 at your Memory speed. I say this because we'll be losing memory speed at our best settings at that point. Only use a Higher Divider IF your CPU speed will bring your Memory speed to within 2-5 MHz of your MAX Memory Speed. 240HTT X10 = 2400Mhz, Divided By 11 (166) brings out Memory down to 218Mhz If out MAX speed as 236, we're Giving away Memory bandwidth for no reason. However, if your Max CPU bus is 260, then we get this 260x10 = 2600 /11 = 236.
    See how that works? Now out Memory is maxed AND out CPU is maxed....

    Hope this helps.
  3. YellowC4S

    YellowC4S TS Rookie Topic Starter Posts: 107

    don't forget this
  4. wolfram

    wolfram TechSpot Paladin Posts: 1,967   +9

    This is an excellent guide.
  5. MetalX

    MetalX TechSpot Chancellor Posts: 1,388

    Maybe it's not because it exists on another website as well. I'll bet it won't be a sticky unless there is some proof that YellowC4S is the person who wrote the original guide on the other website and didn't just copy and paste it onto here. The guide seems to have come from here:


    It is pretty much an exact copy of what Yellow posted... I assume you ARE the author or that original guide Yellow?
  6. wolfram

    wolfram TechSpot Paladin Posts: 1,967   +9

    That's correct MetalX. It was a copy & paste job. Still nice guide though....
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