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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Deathcharge - Saturday, October 15, 2005 - link
also what do you think of opteron 144 or 146? the 144 are very cheap and they OC quite well apprentlypmorcos - Thursday, October 13, 2005 - link
Before I comment, you should know that I have been overclocking for 8 years now and literally overclocked all but one of the chips you mentioned in the beginning of this very good article. The HT multiplier was new to me with my most recent DFI NF4-SLI-DR board so I found that extremely useful and plan to see if I can up my speeds...but I digress.I think it would be extremely valuable to TRY to put in words the order with which an overclocker should approach making changes to settings. In other words, which is likely to be the most limiting/critical aspect(s) and from there tweak the others to max the system out.
It would be interesting to say, for example, that you start with a "safe" power settings (which is pretty obviously the limiting factor). For example, let's say your CPU and memory are rated at 1.3 and 2.8 V respectively. Why not go straight to "safe" settings for the two and tweak from there? It seems that the most useful piece of information that is NOT provided by anandtech or anyone else for that matter is a voltage and temp graph of stability/viability for these chips. It would be simple to take 3 samples (at a cost) of each chip and run the test with "average" cooling and find out what is "safe". For example if running all stock settings but upping voltages to say 2.4/3.6 V in the example above, you might see stability up to 1.65 / 3.1 V with the parts catching fire at say 1.8/3.3 V or stable at temp readings for cpu/memory of 44/47C but unstable above that. Once armed with these two graphs of information averaged from 3 chips tested the rest is very straight forward.
You simply set the cpu volts to 1.65 and memory to 3.1 V (the safe settings; check real voltages vis bios monitoring) and now you up your fsb and tweak your memory timings and in a few minutes you are running max.
Why do I think this is more valuable that showing us a graph of your results? Because like many I'm squeemish about upping the voltage on my processor and memory. I'm worried much more about the power-on affects than I am the "long-term" effects.
In computers, there are no long-terms for an overclocker. An overclocker's comp is 60% hardware and 40% software. Their greatest joy is in posting results on their favorite forum. I want to know that when I hit the power button...that the 1.7V setting does NOT have a 10% chance of blowing my processor.
My ramblings. Thanks again for another great article from by far the VERY BEST place in the world to find out how computer parts work.
JarredWalton - Thursday, October 13, 2005 - link
Thanks pmorcos.I'm working on the X2 3800+ OC followup, and I've gone back and done further testing of temperatures and voltages. Chips differ, so the real advice I have on that subject is to test your own chip extensively. I've heard of people doing 2.8 GHz on 1.500V with the Venice chips, but mine won't even POST at those settings. I think 1.65 or 1.70V was required to POST, and even then I couldn't run stable benchmarks without more voltage.
I will also be trying to cover a bit more of the "how to" process in the next one. Consider this the foundation, and the next article will refine the approach a bit. Your comments on what you'd like to see more of are definitely welcome, though, and I'll try to address the order and approach I take next.
Concerning another comment: "I want to know that when I hit the power button...that the 1.7V setting does NOT have a 10% chance of blowing my processor." I'm not quite sure I understand the concern or know how to test that. Are you saying that the power on process has more voltage fluctuations and may therefore toast the CPU in the first second? (I haven't had that happen over the past several months of testing this chip and others in overclocked setups.) I must admit that I'm extremely nervous about the 1.850V I used for running at 2.80 GHz, but even then the chip continued to function (for now - heheh).
Cheers!
Jarred Walton
WhipperSnapper - Thursday, October 13, 2005 - link
That was one of the best computer enthusiast website articles that I've read in a long time, but perhaps I don't get around too much. I'd like to hear more about the problems that spilled over to other components, such as the SATA hard drive (mentioned in the Final Thoughts) and whether or not the overclocking can be isolated to the CPU and RAM. I also wondered if there was a reason why you guys used a SATA hard drive and not an IDE drive and whether overclocking requires a SATA hard drive. (I don't see why it would.)
Also, have you guys tried to do any tests using memory stick heatsinks? Do they actually do anything? That subject might make for a worthwhile article on its own--RAM cooling.
aptinio - Saturday, October 8, 2005 - link
bravo! great article. very informative but not too bloated. can't wait to finally upgrade my amd k6-II with 1mb l3 cache on the motherboard! lol!Kougar7 - Thursday, October 6, 2005 - link
Thank you for the excellent, comprehensive, and very thorough article! :-) It must have taken a massive amount of work and time to complete. It’s answered my recent musings about my own Crucial value ram, which looks much nicer now! It’s also solved a question about OCing with recent AMD 64 chips, amongst also correcting a few personal misconceptions I’ve had.I just wish to ask if you plan to include a similar article on OCing with P4s? I personally run a 2.8C (Northwood) @ 3.4 rock solid at the 3.4C’s default voltage, but am now wondering exactly what performance hits, if any, that I’ve taken from having to use a 5:4 CPU:DRAM ratio instead of the previous 1:1, even though I’ve kept it at DDR390 and the timings better than specs.
I’m planning to bench the differences from a 1:1 ratio, a 3:2 ratio at highest speed I can get (sub-DDR333), my current setup, and finally one other setting where I got the value memory to run 2-2-2-6 timings, to get a more solid idea on which performs best with some solid figures.
Although the core and the platform itself both have both changed, I’d still be interested in a Intel processor based test! Perhaps instead of a P4, maybe a Pentium “D” OCing article similar to what you have planned with the X2 3800+? ;-)
I’m very much looking forward to your X2 3800+ OCing review!! You rock :-D Thanks in advance for it!
JarredWalton - Thursday, October 6, 2005 - link
I'm trying to get a socket 775 motherboard that will overclock well with Pentium D 820. Once I get that, I can give it a go. I've also got a Pentium 4 505 and a 540 that I want to run some similar tests on. First, though, I need an appropriate motherboard.clue22 - Thursday, October 6, 2005 - link
so basically what the everybody is saying about the value RAM vs. low latency more expensive RAM is that for the athlon 64 it is basically a waste of money (i.e. you only get about 5% performance gain), but usually spend 100% or more money to get the "better" RAM. i have to build a couple of systems pretty soon and now i believe that my money would be better spent on 2GB of value RAM vs. 1GB of the more expensive stuff. does anyone know of a test that has been run with 2.5-3-3-8-1t vs. 2-2-2-5-1t? also why does every mid-range/gaming/hot-rod price guide ever recommend the either the samsung tccd (or tcc5) or winbond bh5/ch5 based memory if it has so little effect on performance. finally is it even important anymore (if it ever was) to get matched pairs of memory that are bundled together (supposedly manufactured at the same time)? i was looking at some corsair (had good experience with them in the past) xms3200xl RAM but now i think i should get more of their value select memory instead.thanks
RupertS - Wednesday, October 26, 2005 - link
so basically what the everybody is saying about the value RAM vs. low latency more expensive RAM is that for the athlon 64 it is basically a waste of moneyThis may not be a general rule.
It may just be that at this stage of development for GPU's, CPU's and memory, memory has more than enough capacity - it is not the choke point. If GPU and CPU speed were to improve while memory speed stayed the same, you might reach the point where increasing GPU and CPU speed was non-productive for games, while overclocking memory provided large performance improvements.
rabbit fighter - Wednesday, October 5, 2005 - link
Where was this explained? He said the 3200 was better in the first paragraph and that he would explain later, but I can't find the later explanation!