Investigations into Socket 939 Athlon 64 Overclocking
by Jarred Walton on October 3, 2005 4:35 PM EST- Posted in
- CPUs
Power Supply
Despite what manufacturers might want you to believe, power supplies are less about wattage and more about the amount and quality of current that they can supply. In theory, the Watts rating of a PSU can be determined with the current and voltage ratings. Using the equation P = I x V (Power = Current x Voltage), you can come up with a Wattage for each voltage that the PSU provides, add them all together, and you have the rating. Simple enough, right? Unfortunately, there are problems with this method of rating a power supply.
The biggest problem is that PCs don't require equal amounts of power from each voltage, and the wattage rating simply serves to obfuscate the real power levels. The +12V rating is generally the most important rating, and modern ATX2.0 PSUs actually require two +12V rails (i.e. outputs form the PSU). Two 500W PSUs from different manufacturers could actually have wildly different characteristics in the type of power that they provide. In a really bad PSU, reality can be further distorted by providing high output ratings on the -5V and -12V lines. Computers draw very little power from the negative lines, so if a PSU were to rate the -12V line at 3A instead of a more common 1A (or less), they can inflate their wattage by 25W or more. As if that isn't bad enough, there are even more ways to "cheat" the rating.
Temperature plays a role in determining the output capacity of a power supply. You can read about it elsewhere, but the main concept is the following: "The thermal capacity of materials changes slightly with temperature primarily due to changes in density." Part of what allows a power supply to provide current at a specific voltage is the ability to transform the 115V input from the wall (or 230V in other areas of the world) to a different value. Such a change creates heat, and the heat has to be dissipated. Inside a power supply, you will find heat sinks much like what you see on a motherboard, along with a cooling fan or fans. Depending on how the power supply is rated, it might actually provide 450W at 10 degrees C and only 375 W at 30 degrees C. (You'd have to know the specific heat values for the various materials inside a PSU to really be able to calculate how temperature affects the output capacity for a specific PSU.) Nearly all modern computers will have a case temperature in the 30 degrees C or higher range, so a PSU rated using 10-25 degrees C values is far from a realistic representation of the PSU's output capacity.
Lastly, just because a power supply can provide a specific output doesn't mean it can do so well. In the US, power from the wall outlets comes at 115V, but variance is allowed. In fact, the output voltage can fluctuate between 110V and 121V (5%) while still being within spec. That may be fine for some household items like lamps and coffee makers, but computers tend to be a little more demanding in their requirements. A power supply that outputs 3.2V, 4.8V, and 11.5V is still technically within the required range, and there's a good chance that it will work with a typical PC. What really causes problems are fluctuations, which are usually influenced by the use of lower quality components as well as temperature changes. Even though a PSU might work in a regular PC, though, overclocking really pushes things to the limit, and it's far better to have a PSU that can output voltages exactly at spec than a few percent high or low.
One of the easiest ways to determine the quality of a power supply is to simply pick it up. A 500W power supply should weigh quite a bit more than a 350W power supply; if it doesn't, be suspicious. Reading the label on a power supply can be helpful, but that doesn't usually tell you the temperature at which it was tested, and of course, it could always be inaccurate. The saying "you get what you pay for" also applies, so if a PSU costs far less than the rating would suggest, it's likely that the unit isn't really as good as the sticker claims. A better idea is to just go with a respected name, as we suggested with motherboards. Our top picks for PSU manufacturers are Antec, Enermax, Fotron Source, OCZ, and Seasonic. Enermax, OCZ and Seasonic are probably the safest bets, as they don't really have "value" and "performance" parts right now, though the more expensive Antec and Fotron Source units are just as good. If you want a high quality power supply and you're shopping online, here's the fastest test: does it cost less than $75? If so, it's probably a moderate unit, and under $50 is an inexpensive unit. The good power supplies almost always cost $80 or more. If you're not sure, though, ask around! Some times, there are good deals to be had on high quality power supplies.
With all the above talk about getting a quality power supply, we also ran some tests using a cheap PSU that came with an even cheaper case. The case was the MGE and 400W PSU that we recommended in our last Budget Buyer's Guide. The case is flimsy, made of thin aluminum, and the cables for the front USB and Firewire ports were very difficult to work with - they were separated into single-pin connectors rather than a block of pins. It's impossible to say what the long-term reliability of such a case is, but it's been running nearly 24/7 for a couple of months now without any problems. The highest overclocks seemed a bit less stable with the 20-pin power connection, but we did manage to match the overclock of the OCZ PowerStream 600W. Maximum power draw for the test configuration was measured at around 220W, so we never came close to the 400W power rating.
Despite what manufacturers might want you to believe, power supplies are less about wattage and more about the amount and quality of current that they can supply. In theory, the Watts rating of a PSU can be determined with the current and voltage ratings. Using the equation P = I x V (Power = Current x Voltage), you can come up with a Wattage for each voltage that the PSU provides, add them all together, and you have the rating. Simple enough, right? Unfortunately, there are problems with this method of rating a power supply.
The biggest problem is that PCs don't require equal amounts of power from each voltage, and the wattage rating simply serves to obfuscate the real power levels. The +12V rating is generally the most important rating, and modern ATX2.0 PSUs actually require two +12V rails (i.e. outputs form the PSU). Two 500W PSUs from different manufacturers could actually have wildly different characteristics in the type of power that they provide. In a really bad PSU, reality can be further distorted by providing high output ratings on the -5V and -12V lines. Computers draw very little power from the negative lines, so if a PSU were to rate the -12V line at 3A instead of a more common 1A (or less), they can inflate their wattage by 25W or more. As if that isn't bad enough, there are even more ways to "cheat" the rating.
Temperature plays a role in determining the output capacity of a power supply. You can read about it elsewhere, but the main concept is the following: "The thermal capacity of materials changes slightly with temperature primarily due to changes in density." Part of what allows a power supply to provide current at a specific voltage is the ability to transform the 115V input from the wall (or 230V in other areas of the world) to a different value. Such a change creates heat, and the heat has to be dissipated. Inside a power supply, you will find heat sinks much like what you see on a motherboard, along with a cooling fan or fans. Depending on how the power supply is rated, it might actually provide 450W at 10 degrees C and only 375 W at 30 degrees C. (You'd have to know the specific heat values for the various materials inside a PSU to really be able to calculate how temperature affects the output capacity for a specific PSU.) Nearly all modern computers will have a case temperature in the 30 degrees C or higher range, so a PSU rated using 10-25 degrees C values is far from a realistic representation of the PSU's output capacity.
Lastly, just because a power supply can provide a specific output doesn't mean it can do so well. In the US, power from the wall outlets comes at 115V, but variance is allowed. In fact, the output voltage can fluctuate between 110V and 121V (5%) while still being within spec. That may be fine for some household items like lamps and coffee makers, but computers tend to be a little more demanding in their requirements. A power supply that outputs 3.2V, 4.8V, and 11.5V is still technically within the required range, and there's a good chance that it will work with a typical PC. What really causes problems are fluctuations, which are usually influenced by the use of lower quality components as well as temperature changes. Even though a PSU might work in a regular PC, though, overclocking really pushes things to the limit, and it's far better to have a PSU that can output voltages exactly at spec than a few percent high or low.
One of the easiest ways to determine the quality of a power supply is to simply pick it up. A 500W power supply should weigh quite a bit more than a 350W power supply; if it doesn't, be suspicious. Reading the label on a power supply can be helpful, but that doesn't usually tell you the temperature at which it was tested, and of course, it could always be inaccurate. The saying "you get what you pay for" also applies, so if a PSU costs far less than the rating would suggest, it's likely that the unit isn't really as good as the sticker claims. A better idea is to just go with a respected name, as we suggested with motherboards. Our top picks for PSU manufacturers are Antec, Enermax, Fotron Source, OCZ, and Seasonic. Enermax, OCZ and Seasonic are probably the safest bets, as they don't really have "value" and "performance" parts right now, though the more expensive Antec and Fotron Source units are just as good. If you want a high quality power supply and you're shopping online, here's the fastest test: does it cost less than $75? If so, it's probably a moderate unit, and under $50 is an inexpensive unit. The good power supplies almost always cost $80 or more. If you're not sure, though, ask around! Some times, there are good deals to be had on high quality power supplies.
Click to enlarge.
With all the above talk about getting a quality power supply, we also ran some tests using a cheap PSU that came with an even cheaper case. The case was the MGE and 400W PSU that we recommended in our last Budget Buyer's Guide. The case is flimsy, made of thin aluminum, and the cables for the front USB and Firewire ports were very difficult to work with - they were separated into single-pin connectors rather than a block of pins. It's impossible to say what the long-term reliability of such a case is, but it's been running nearly 24/7 for a couple of months now without any problems. The highest overclocks seemed a bit less stable with the 20-pin power connection, but we did manage to match the overclock of the OCZ PowerStream 600W. Maximum power draw for the test configuration was measured at around 220W, so we never came close to the 400W power rating.
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JarredWalton - Wednesday, October 5, 2005 - link
Sorry if I missed this in the article. The reason a 3200+ may be better is the 10X multiplier vs. 9X. Sure, the DFI board used worked pretty well at either setting, but there are many boards that won't handle much above 250 MHz CPU bus stably. Needless to say, there's a reason 2800 MHz was only included at one setting. While it still wasn't stable, it would actually run most benchmarks at 10x280. 9x311 wouldn't even load Windows half the time. The extra $50 for added flexibility is also nice: you can try 9x300, 10x270, PC3200, PC2700, etc. to find the most stable, highest performing option.Bakwetu - Wednesday, October 5, 2005 - link
Thanks for a great article. I haven't been following the development so carefully since I upgraded last time (with one of the last unlocked Barton 2500+), so this article was a most welcome refresher for me, as I will probably get a x2 3800 rig in the near future.Last time I checked using the naked fingertip to smear out the paste was a big no-no. I have always used either a washed razorblade or fingertip in a clean plastic bag. The Arctic silver once sold without silver was a faked, copied product as far as I know. The real stuff in its many forms over the years has definitely shown that it is a good product.
javalino - Wednesday, October 5, 2005 - link
Frist , great article, Jarred.Second, i m an anand fan since i remember (1999-2000).
Third, Since yours conclusion focus on a dilema about overclock, why spend to much in an overclock symtem(or on a powerfull system) if you target is at games ? (wich is a GPU limited). An 125 bucks , like you said, will be more usefull in a video card.
My idea is an article, about "Benefits, Costs, and Lessons Learned" about build a system for games. How much will be a performance gain from systems running high end cards ,at high resoltion and configurations ( like 1600 x 1200, and with an extra 4xAA 16XAF), with differents system . A FX VS 64(overclock) VS P4 (over) VS P-M VS AMD XP (over of course), for example. The conclusion will be, how much is "needed" to pay for a decent game machine wich is possible to play all current games(and maybe future) with great image quality and performance.
Maybe the answer is obvious, go with the best FPS/price option possible, or maybe not.
AtaStrumf - Tuesday, October 4, 2005 - link
Great article Jarred!!! I really like your choice of value parts and how you criticaly assesed the results based on the bang-for-the-buck. And finally you did away with pages and pages of bar charts, and combined them into line-scaling charts. How long have I been asking for something like that??? Now we can finally see the REAL difference (or lack of it), and analyse results properly, without having to go back and forth between tens of bar charts. Tell Anand to upgrade your graphing engine ASAP.I am a little worried about those voltages though. This sure looks like a bad chip to me (OC wise). WAY too high voltages. I would not go over 1,45 - 1,50 V or else you risk screwing up the chip. You see the memory controller on the chip doesn't like too high voltages and though it will still work, the chip will get slower eventually. Hard to explain really but I know my new 2,2 GHz A64 is faster and much cooler than my old 2,4 GHz A64 (same core - Newcastle, same cooer, same RPM, same case, same ...), which I bought from some crazy overclocker (last time BTW). The 2,4 GHz one gave me really shitty results in FAH for weeks. That's the only explanation a have so far anyway. Maybe you can do an investigaion into this -- burn in one A64 Venice at say 1,6V 24/7 for a few weeks and let's see what happens. I just don't have the $$$ and time to take the risk. I'd be very happy to hear from other forum members on this as well.
Anyway, glad to see at least part of AT is back to the high quality standards we were used to.
AtaStrumf - Tuesday, October 4, 2005 - link
Or maybe it's the SOI process that is to blame for not taking high voltages too kindly, or maybe both, don't know yet, but I would definitely advice caution goint over 1,5V (default for 0,13 mikron SOI chips). Just think about it, that's already a 15% increase. +10% is usualy max that is still considered safe.You just posted that this chip seems to have changed it's behavior (better OC). That may have something to do with the high voltages and it may not be all good. I'd suggest testing it again in a few benchmarks and comparing the results.
JarredWalton - Wednesday, October 5, 2005 - link
Working on it. I think I ended up benching at 1.850V for the 10x280 setting and then not dropping voltages as much as I was supposed to. I'm a little skeptical that a CPU would get slower, though. Usually, they work or they fail. We'll see.My thought on the "safe limit" though: what voltage does the FX-57 run at? Whatever it is, at 10 to 15% to that and you're probably still okay. Good cooling will also help; on the stock HSF, I'd be a lot more nervous going over 1.550V.
OvErHeAtInG - Tuesday, October 4, 2005 - link
Very useful article - thorough yet concise. And I would like to toss in another request: Add to the test a ULi-based motherboard (such as the recently reviewed ASRock 939Dual-SATA2). How do these Venices overclock when you can only feed them +.05v? As I recall the standard AT Clawhammer was used in that review.That would be hugely useful to a lot of us wanting to transition to A64. While the thing to do is probably just get a DFI or other top-end oc'er, what to do for those of us who are not yet ready to upgrade GPUs? On second thought: you could simulate the ASRock motherboard by simply setting the Venices to the lower voltage, on the DFI board, and testing for the max overclock on that. I think that would vary quite a bit from chip to chip, but just to get an idea - how much of a disadvantage is being limited in your voltage? Food for thought.
JarredWalton - Tuesday, October 4, 2005 - link
I played around with voltages a bit more last night. It seems like I can hit about 2.40 GHz with only increasing the CPU voltage to 1.40V, though I didn't run all of the benchmarks to fully test that config. I'm not sure if the CPU has changed behavior over the past month, or if I was just too liberal with the voltages initially.For the ASRock, that Wes managed to get a 500 MHz OC even with the minimal voltage adjustments is promising. Truth be told, the DFI Infinity seems to undervolt the CPU slightly, so 1.500V actually shows up as closer to 1.455V. If the ASRock is exact with the voltages, or even a bit high, I think a 2.4+ GHz overclock is a reasonably safe bet.
OvErHeAtInG - Wednesday, October 5, 2005 - link
Thanks for the info, Jarred. I'm sure there's a thread on this somewhere.... :)araczynski - Tuesday, October 4, 2005 - link
i haven't seen a better argument for not wasting money on the 'better' memory in ages.with those kinds of 'gains' i congratulate the companies for milking everyone with their markups for the 'higher end' components.