AMD's SB750: Enabling Higher Phenom Overclocks?
by Gary Key on July 23, 2008 12:00 AM EST- Posted in
- CPUs
Higher Overclocks in Vista 32-bit vs. 64-bit?
In preparation for this article we also wanted to test one more theory: that Phenom overclocks better under 32-bit Vista than 64-bit Vista. The basis for this theory is that the number of active registers increase in 64-bit mode, which creates additional workload routines that leads to increased transistor switching that ends up increasing thermals and loads on the IMC. Well, you get the picture, not exactly a cycle of events that would lead one to believe an already clock starved core design has a chance when moving to a 64-bit environment, well at least Vista 64-bit. In case you're wondering, Intel CPUs seem to overclock the same regardless of OS but just for kicks we tried our 9850 under the two OSes to see how things differed:
| Phenom 9850BE - Highest Core Speed / HT Ref Clock Vista 64 versus Vista 32 |
||||||
| Core Speed | HT Ref Clock | HT Link Speed | North Bridge Speed | Memory Speed | CPU VID | |
| Foxconn A79A-S ACC On - Vista 32 | 3382 | 205 | 2050 | 2255 | 1093 | 1.4750V |
| Foxconn A79A-S ACC On - Vista 64 | 3280 | 205 | 2050 | 2050 | 1093 | 1.4625V |
| . | ||||||
Strangely enough, our highest HT overclock with the 9850BE was bested by 102MHz in core clock speed and a 205MHz improvement in NB speed under 32-bit Vista. It's not a huge advantage, but something we were definitely able to identify and confirm on a variety of settings with several different processors.
| Phenom 9850BE - Highest Core Speed / HT Ref Clock Vista 64 versus Vista 32 |
||||||
| Core Speed | HT Ref Clock | HT Link Speed | North Bridge Speed | Memory Speed | CPU VID | |
| Foxconn A79A-S ACC On - Vista 64 | 3000 | 200 | 2000 | 2200 | 1066 | 1.3500V |
| Foxconn A79A-S ACC On - Vista 32 | 3150 | 210 | 2100 | 2520 | 1120 | 1.3500V |
| . | ||||||
The biggest difference we noticed between the two operating systems and overclocking occurred when we significantly raised our NB speeds and trying to increase HT ref clock with this particular CPU. We just could not run high NB speeds under Vista 64 in the sweet spot for this processor, which is around 3.0GHz at fairly reasonable voltages. We are still testing this phenomenon (pun not intended) as our 9950BE clocks at nearly the same rates under each OS.
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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.