Athlon Dual Core: Overclocking the 4200+ The official introduction of the Dual-Core or X2 Athlon 64 happened at Computex the first of this month. As you saw on AnandTech in the performance of the AMD Dual-Core desktop was stellar.
The pricing, however, was a little hard to swallow with the range from just over $500 for the lowest-priced 4200+ to around $1000 for the top-line 4800+. To refresh your memory, there are really very few differences between processors in the X2 line: There are really just two speeds - 2.2GHz and 2.4Ghz - and either 512KB cache on each CPU or 1MB cache on each CPU. In addition nearly any Socket 939 motherboard can in theory run the new Dual-Core Athlons, as all that is required is a BIOS update. Now that the Dual-Core AMD processors are starting to appear in the market, we have received many emails asking which X2 is the best value. With prices so high that is a very fair question. To shed some light on the answer we decided to take the X2 entry level $500 4200+ to the limit on our DFI nForce4 platform to see what we could really achieve with basic air cooling of the 4200+.
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Friday, June 24, 2005 - #42 & #35 - To bring the news to you first, our ONLY choice is manufacturer-supplied samples. When we test there is usually nothing available in the retail channel. In this case we had one one Retail 4200+ and one manufacturer-supplied 4200+. They performed within 5MHz of each other in overclocking, which is equal performance. Our performance with both processors is lower than sites that publish a screen capture of an OC speed and don't run any benches, so we stand by our results on air cooling. The 'Conspiracy' theory sounds good, and is usually spouted by the manufacturers who didn't do well in a roundup.
In a truly competitive world like computer components there is no point to providing 'cherry' parts to reviewers. If people buy a product due to a review that shows x performance and their part won't do the same they RMA the part. RMA's cost manufacturers lots of money. A high RMA rate will quickly kill any profits on a product. Even memory - a business based on binning or hand-picking of parts for performance - has settled down on cherry parts.
Manufacturers who tried that got burned on RMAs and came back the second time with representative parts. There is always variation in overclocking results, but huge variation from reported results are someone who doesn't know how to overclock, a change in parts used (which is why overclockers are big on production weeks), or a change in binning (selection criteria). Specializing in certain review areas, as we do at AnandTech, makes you a lot less stupid and easily duped than you might imagine.
T HOSE OF YOU WHO REGULARLY PERUSE the news here at TR probably saw about the Athlon XP-M 2500+ and its recently discovered overclocking potential. The chips have become so popular so quickly that their street price has jumped 33% in recent days. Of course, given the accounts of overclocking to 2700MHz 'on air' (using only a heatsink/fan) it's no wonder they're so popular. Needless to say, we couldn't sit this one out, so last week we ordered up an Athlon XP-M 2500+, and have spent the last 24 hours or so putting it through its paces.
Amd Athlon Overclocking Software
Read on to find out more about this overclocking wonder, and see how our particular chip fared. XP-M: It's not just for notebooks anymore The first question in many people's minds is: What's up with putting a mobile chip in a desktop system? Well, there are a couple of important factors that make the XP-M such a desirable chip from an overclocking standpoint. The first is the default voltage of the chip. Desktop Athlon XP 2500+ chips run at a frequency of 1.8GHz using a default voltage of 1.65V. That's fine for desktop systems that don't have to worry about power consumption or battery life, but it's a different story for mobile systems. Because voltage relates directly to power consumption, one way to cut down on the amount of power used in a mobile application would be to lower the core voltage of the processor.
Of course, it's not quite that simple. Some 2500+ chips may continue to run properly at 1.8GHz if their core voltage is set below 1.65V, but others may become unstable or crash outright at anything below 1.65V. Every chip is different in this regard, and you won't know until you try.
AMD does in fact use this method for the Athlon XP-M. Basically, they test their chips and determine which 2500+ chips can maintain their 1.8GHz clock speed properly with only 1.45V of core voltage instead of 1.65V.
Chips that pass this test can then be set to a default voltage of 1.45V and sold as Athlon XP-Ms. Essentially, the XP-M 2500+ is the cream of the crop within its speed grade. Not only can it do 1.8GHz, it can do it with one hand tied behind its back, so to speak. Up close: our Athlon XP-M 2500+ Typically, overclocking is a crapshoot because you never know how fast a particular chip is going to go. There are many tales of people taking Pentium 4 2.4Cs and overclocking them to 3.2GHz or higher with ease, but we have an example in our labs that refuses to go any higher than 2.6GHz. Overclocking a processor is like a box of chocolates.
In the case of the Athlon XP-M, however, AMD has basically created a part consisting of cherry-picked processors. After all, if a 1.8GHz chip is good enough to stay at 1.8GHz even when undervolted by 0.2V, how much higher than 1.8GHz might it go at default voltage? This is one big reason for the XP-Ms popularity with overclockers; grab an XP-M, and you know you're getting something good. The only question is: how good? The second important mark in the XP-M's favor is what's missing: a multiplier lock. AMD mobile systems use the PowerNow!
Power management feature to conserve battery life. Unlike a desktop system, where bus speed times processor multiplier equals processor speed, things in a PowerNow! System are much more fluid. The processor has a minimum and maximum speed, and the system is constantly adjusting CPU speed based on processor load. If your system isn't working very hard (you've gone to lunch, or you're working on a Word document) the processor will limp along at 800MHz.
Fire up a game, and it may jump up to 1500MHz and stay there until you quit. The speed is constantly updated relative to system load, and can be set to any number of intermediate speeds between the minimum and maximum. One of the ways that the system works this magic is by manipulating the multiplier on the processor. Thus, in order for PowerNow!
To work, the processor's multiplier must be unlocked. Since PowerNow!
Is an important part of AMD's mobile strategy, all Athlon XP-M chips are factory unlocked. Add these two factors together, and you wind up with a guaranteed high-quality, unlocked Athlon XP core for only $25 more (at the time of this writing) than a 'regular' Athlon XP 2500+. Whatta bargain!
Putting theory into practice So now that we've looked at why the XP-M should be a good overclocker, let's see if our hypothesis holds up to the test. Our subject is an Athlon XP-M 2500+, manufactured in week 49 of 2003, with a stepping code of IQZFA.
The markings on each chip betray its origins We started out on an Asus A7N8X motherboard, and quickly got the CPU up to 2.4GHz@1.8V on a 200MHz front-side bus with little drama. Any attempts to push harder, however, were met with failure, possibly because the A7N8X refused to crank the voltage any higher than 1.825V.
At that point, we switched over to Abit's new nForce 2 Ultra 400 board, the AN7 (review forthcoming). The AN7 had no qualms about pushing the voltage up to and past our own comfort level. In the end, though, it didn't make much difference with this chip.
We managed to get 2.5GHz@1.96V (yes, 1.96, that's one of the settings on the AN7), but it wasn't stable enough to complete our benchmark suite, so we decided to back down to 2.4GHz at 1.8V and run our benchmarks there. Our open-air test bench with Abit AN7 motherboard and bone-stock air cooling Abit's uGuru utils kept us aware of our temps, shown here at 2.4GHz and 1.8V Although we didn't hit the 2.7GHz+ levels that some others have apparently reached, let's not lose sight of what we did accomplish. This is a 33% overclock resulting in a 200MHz advantage over an Athlon XP 3200+ (currently going for $195), from a chip that cost $98. We decided against experimenting with bus overclocking, because our intent was to test the processor's capabilities, and bus overclocking would've thrown too many other variables into the equation, such as non-standard PCI and AGP clock speeds.
We said it before, but it bears repeating: One of the big advantages of the XP-M is its unlocked multiplier, which allows for substantial performance gains without having to resort to bus overclocking.