AMD's SB750: Enabling Higher Phenom Overclocks?
by Gary Key on July 23, 2008 12:00 AM EST- Posted in
- CPUs
Final Words-
Actually, these are not our final words as we have significantly more testing to complete on newly arriving boards with the soon to be introduced SB750 South Bridge. So where do we start?
Let's see, AMD has introduced a new South Bridge that is certainly an upgrade to the long in the tooth SB600 and also addresses one feature flaw in the SB700. That feature flaw is RAID 5 and while we are not proponents of host controller RAID 5, early indications is that AMD's implementation is no worse than NVIDIA's or Intel's current solutions. Marketing can check that one off the feature list now. However, we are still disappointed in the PCIe 1.1 interface to the 790FX/780G and upcoming new NB chipsets.
AMD is probably correct that there is plenty of bandwidth available with the current solution, but we cannot help but wonder why they did not include a PCIe 2.0 interface given the amount of time this chipset has been under development. Also, the lack of a native LAN interface is perplexing, not from a performance viewpoint, but the fact that additional costs are incurred by the motherboard companies and ultimately users for the additional interface components. For a company that is specializing on reduced cost and highly integrated solutions, this one is perplexing. However, in the end, the performance of the SB750 rivals that of its competitors at this time, or comes close enough in current testing that we can overlook our. Speaking of performance, early numbers (just received final chipset drivers and late beta RAID drivers) indicate a slight improvement over SB700 but well within the error of margin in our storage test suite.
Of course, the big news is the new low level interface between the SB750 and the Phenom CPU. Advanced Clock Calibration is its name and overclocking is its game (a bad throwback to days gone by). In all seriousness, ACC works and depending on just how "substandard" your Phenom might be at overclocking, it works extremely well. We have several theories about what this interface does and how AMD is doing it, but without explicit information or conformation from AMD we will have to continue theorizing about it. Our testing continues for the new product launches next week, but we were satisfied enough with the current numbers to publish early results. What we are not satisfied with is the lack of information from AMD, but that is their prerogative.
Our test results confirm AMD's statements that a 100MHz to 300MHz improvement in Phenom core speeds are attainable with ACC. This is not a guarantee and some processors will require significantly more tuning than others to get up to speed, but overall our experiences to date with several processors are very positive. Our otherwise clock challenged 9850BE suddenly started acting like a Tour de France rider on steroids with ACC enabled. Our clock improvements ranged from 200MHz to 410MHz depending upon our settings. What was particularly interesting is the fact that our largest improvements occurred when we tried raising HT ref clock and increasing the multiplier at the same time.
Our 9850BE responded especially well in this case with ACC enabled, so much so that we wondered if maybe our original settings were completely off. They were not as it turns out after a few hundred reboots between setting changes on several boards. We also found it was much easier to sustain a high NB speed with ACC enabled and this lead to several significant improvements in memory performance. Finally, we found leaving the program on auto settings provided the quickest and easiest overclock improvements, at least with our processors. Utilizing AOD was much simpler than making constant changes in the BIOS, but in the end, neither one offered an improvement over the other one in performance.
We purchased a retail processor that seems to have been blessed by the processor Pope before it left the FAB and arrived in the office. As such, we only recognized a 100MHz improvement in core speed with ACC enabled on the Foxconn board. We were able to tune the SB600 equipped ASUS board to the point where the difference was only 50MHz at the top end. What we did not report on today since we are still verifying the test results, is that ACC did make a significant difference in NB speed with this processor in the midrange clocks from 3GHz to 3.2GHz with NB speeds ranging from 2520 to 2600 at these speeds. Compared to the Foxconn board with ACC turned off or the ASUS board, our maximum NB speeds hovered around 2200 to 2400 with slightly more CPU and NB Vid required.
AMD informed us that we should be able to run lower voltages and improved HT ref clock speeds with the Phenoms. We are currently testing these claims but at this point we do see lower voltages being required at a variety of clock speeds but have not noticed any true improvements in HT ref clocks, yet. As always, your mileage will vary depending upon your CPU and motherboard, but we believe most users will see some improvement, maybe not enough to spend additional money on upgrading the motherboard. That said, we feel like this technology will benefit the enthusiast and feel like it is probably a safe purchase at this time for those users who have to have the latest and greatest technology.
The complaints about the Phenom processor not clocking as well under Vista 64 when compared to Vista 32 are for the most part true. We had varying degrees of separation in the final core speed numbers depending upon settings, enough so that we would have to recommend XP Pro or Vista 32 over their 64-bit counterparts for those who need to squeeze the last ounce of performance from their systems. Once again, the differences varied greatly depending on the motherboard, processor, BIOS settings and if ACC was enabled or not. While the final system settings under Vista 64 were acceptable to us, we know for many this will not be the case. We hope to have some answers soon from AMD.
In the end, we know after a good 60 hours of testing, over 600 different settings, 400+ screen shots, and countless reboots that Advanced Clock Calibration works, yet we do not know anymore about the inner-workings of ACC at this point than SpongeBob SquarePants.
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Maroon - Thursday, July 24, 2008 - link
"We can't help but wonder if it is because AMD is going a little too far in the sacrifices it's willing to make in the quest for higher clock speeds." Hello? This is the one thing that keeps the latest generation AMD procs from being competitive with Intel's. Are we sacrificing stability that you're not telling us?And then the bitching about the integrated LAN...please? Sounds like you guys are just pissed that AMD won't tell you the new SB works.
ughtas - Thursday, July 24, 2008 - link
I remember from months ago, that the L2/L3 cache performance was changed to support larger cache sizes. Is it possible that the tweaks that ACC makes to the processor timing improve the cycle time or allow better lookahead?nubie - Thursday, July 24, 2008 - link
I for one am glad to see an AMD processor at 3.4ghz, if this is a new trend I am all for it.I want to know what kind of clock-for-clock performance this has compared to an Intel, just for kicks.
I had a chat with a knowledgable IT guy, he claims that Intel systems boot faster to a usable desktop than AMD, and he has side by side bench tested them.
I didn't think to ask if he had done tests with comparable level 2 cache, an area that I think may be causing problems, AMD has no processors with 1M level 2 cache except a few older 90nm cores. They are just giving up in this area to Intel.
I applaud them for making neat server processors, but 512k level 2 cache is not cutting it these days.
I have been running on a Core2 "solo" Celeron 430 @2.4ghz for the last several months, and I must say while it is pretty damn fast there are times when it seems to "lock" or "micro-freeze" when it is doing a lot of multitasking.
Xray1 - Thursday, July 24, 2008 - link
Na, the L2 cache is pretty unimportant for AMD processors, as the on chip memory controller is very fast. For example, the difference between 1M L2 and 512k L2 K8 processors at otherwise same speed is for most apps somewhere in the range of 0-5%.Your single core Celeron locks in multitasking, because its single core.....single core is completely obsolete these days.
As to the boot speed: This heavily depends on the system config, bios etc. Plus: How often do you boot? I do that once a day and don't really care if it takes 30 sek more or less.
Xray1 - Thursday, July 24, 2008 - link
One reason for the proprietary 6pin connection between SB and CPU could be: It's simply a hardware dongle to ensure the best possible oc results can only be found on AMD chipset mainboards......It is very hard to believe AMD could not have made the same thing possible by MSR programming in the CPU.If AMD does not get more specific on this, we need true hardware nerds to sniff on these 6 lines and try to reverse engineer what's happening on them.
pmonti80 - Thursday, July 24, 2008 - link
Not so fast my friend.Just look here:
http://www.overclockers.com/tips01369">http://www.overclockers.com/tips01369
Now we have a more plausible explanation that does not involve strange "black magic".
ACC is just another form of CPU skew.
No big deal for anyone, end of the story.
ZootyGray - Friday, July 25, 2008 - link
Your linked source is not saying what you are saying. It's a guess. and conclusions are stated as being based on the assumption that the guesses and assumtions are true.Your attitude overrides that - NOT END OF STORY. And the results reported here stand untouched by your opinion based on what someone else said is assumption and guess. (right or wrong).
Additionally the author of your referenced article is very gracious in excusing himself if his guesses and assumptions are incorrect. And yet he ungraciously comes down pretty heavy in ending his article. And that is what has triggered your own feigned knowledgeable statement.
Maybe it is true - and maybe not. But oclokrs must live in perpetual embarrassment if it is true - and you embarrass yourself in the face of hard testing and accurate reporting of results of that testing. If I wanted speculative guessing and assumption and self agrandisement based on possibly erroneous opinion, I would go read bullshit at toms bubblegum guide. You might enjoy that more since you are apparently so inclined.
You put 60 hours work behind your statement and you might understand a cheap slap.
pmonti80 - Friday, July 25, 2008 - link
You are right on my attitude about last post. Sorry about that.But still I think the analysis of what could be happening here (based on both articles) is probably more in the line of CPU skew or some similar thing. It seems way easier to do with just 6 pins (4 or 5 really usable for ACC).
ZootyGray - Friday, July 25, 2008 - link
I agree with you. And it seems plausible (at least) that skew is quite probably it. The report however is about facts and not /guess /assumption /opinion - and therein is it's value.I fully expect that some will hack into this secret - much like was done before with AMD cpu's when they used the graphite pencil trix - it was all great.
Perhaps I owe an apology to you. I am a little overzealous since I have been seeking a factual, scientific review/testing site for some time. I like what's happening here. I hope I did not come down too heavily on you and the useful info that you presented. (altho the 'embarrass' part in that info,is merely abuse and useless shaming - essentially the stuff of flamewar, ego and fear (which reflects on the author).
Your point is taken and thank you for your (this) reply.
Xray1 - Friday, July 25, 2008 - link
The possibility that it is all about cpu skew/timings does not contradict what I have said. Why do you need a 6 pin connection from a southbridge to the CPU to change these settings? You can do that with simple register programming (MSRs). That's just like what has been done in the past (especially in timing settings of the AthlonXP FSB).So for me the big secret 6pin connection still looks like a big hardware dongle to allow for AMDs overclocking tool to only work on AMD chipset mainboards. They wanted to make it 100% non-software accessible, so there would be no way of doing it on non-AMD chipset boards. That's all I said. And yes, it's also speculation. But as long as they keep it cloed source, it's a non-accessible feature for other chipset makers.