AMD's SB750: Enabling Higher Phenom Overclocks?
by Gary Key on July 23, 2008 12:00 AM EST- Posted in
- CPUs
Testing the Theory - Does it Overclock Any Better?
We started by getting a reference overclock out of one of our Phenom processors, in this case a Phenom X4 9850BE. We picked this processor as it has difficulties clocking past 3.1GHz. In fact, this processor seemed to hit a wall around 3.0GHz and changing the HT Ref Clock past 200 just made matters worse as attainable clock speeds would actually decrease. Even then, we had to tune just about every setting in the BIOS to have a stable platform in the 3.0GHz range. Our initial results with this CPU matched the profile that AMD told us would probably benefit the most from ACC.
We will also provide results with our newly arrived Phenom X4 9950BE that seems to be the pick of the retail lot in early testing. For those of you with the earlier B2 stepping 9600BE, we hope to have results shortly. While ACC should provide benefits such as higher clocks or lower voltages, we were skeptical as to any benefits we would gain with a processor that does not seem to need any tuning. As it turned out, our intuition was almost on the money. We ended up with a 100MHz higher core speed but that was about it. Although not shown, the biggest improvement with ACC came in the 2.6GHz to 3.0GHz range where we could set NB speed to 2.6GHz with absolute stability. With ACC switched off, our NB speed dropped to 2.4GHz and processor voltage at 3.0GHz increased to 1.35V compared to the stock 1.304V.
| Phenom 9850BE - Highest Core Speed / Stock Voltages | ||||||
| Vista 32 | Core Speed | HT Ref Clock | HT Link Speed | North Bridge Speed | Memory Speed | CPU VID |
| Foxconn A79A-S ACC On | 3000 | 200 | 2000 | 2000 | 1066 | 1.312V |
| Foxconn A79A-S ACC Off | 2800 | 200 | 2000 | 2000 | 1066 | 1.312V |
| ASUS M3A32-MVP No ACC | 2800 | 200 | 2000 | 2200 | 1066 | 1.312V |
| . | ||||||
At stock voltages and stock HT/NB speeds, the highest our 9850BE sample would reach was 2.80GHz. This was true on both the ASUS M3A32-MVP as well as the Foxconn A79A-S. Turning on ACC let us hit 3.0GHz without adjusting the CPU's voltage at all. So far, so good.
| Phenom 9850BE - Highest Core Speed / HT Ref Clock | ||||||
| Vista 32 | Core Speed | HT Ref Clock | HT Link Speed | North Bridge Speed | Memory Speed | CPU VID |
| Foxconn A79A-S ACC Off | 3280 | 205 | 2050 | 2255 | 1093 | 1.4250V |
| Foxconn A79A-S ACC Off | 2870 | 205 | 2050 | 2255 | 1093 | 1.4125V |
| ASUS M3A32-MVP No ACC | 2970 | 205 | 2050 | 2255 | 1093 | 1.4000V |
| . | ||||||
This particular CPU acts really strange when trying to increase the HT frequency, anything over 205MHz usually meant decreasing clocks in a hurry, no matter voltages, NB speeds, or HT settings. We found it amazing that turning on ACC all of a sudden allowed a 410MHz increase on the Foxconn board and 310 compared to the SB600 board..all with a minimal increase in CPU voltage.
The CPU would not even post past 2970 on the Foxconn board, regardless of using the BIOS or AOD for clocking, we had to drop to 2870 for stability. On the ASUS board it was fine at 2970 but going over 3GHz meant locks or non-POST situation. There is a wall with this particular CPU and ACC does something for it... that was the one test that just amazed us.. the rest are semi-interesting.
| Phenom 9850BE - Highest Core Speed | ||||||
| Vista 32 | Core Speed | HT Ref Clock | HT Link Speed | North Bridge Speed | Memory Speed | CPU VID |
| Foxconn A79A-S ACC On | 3400 | 200 | 2000 | 2200 | 1066 | 1.4750V |
| Foxconn A79A-S ACC Off | 3100 | 200 | 2000 | 2200 | 1066 | 1.4375V |
| ASUS M3A32-MVP No ACC | 3100 | 200 | 2000 | 2200 | 1066 | 1.4250V |
| . | ||||||
If we simply push for highest core speed, ACC makes a 300MHz difference. Our 9850 could hit 3.1GHz on the two reference configurations, but 3.4GHz was possible on the A79A-S with ACC enabled.
Next we tried a retail Phenom 9950 BE:
| Phenom 9950BE - Highest Core Speed | ||||||
| Vista 32 | Core Speed | HT Ref Clock | HT Link Speed | North Bridge Speed | Memory Speed | CPU VID |
| Foxconn A79A-S ACC On | 3500 | 200 | 2000 | 2400 | 1066 | 1.4750V |
| Foxconn A79A-S ACC Off | 3400 | 200 | 2000 | 2400 | 1066 | 1.4750V |
| ASUS M3A32-MVP No ACC | 3400 | 200 | 2000 | 2200 | 1066 | 1.4675V |
| . | ||||||
Our latest retail Phenom X4 9950 Black Edition overclocks quite well, 3.4GHz isn't a problem. Here ACC doesn't make much of a difference at all, 100MHz is all we get.
We have included performance result screen shots in the following gallery.
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bbqchickenrobot - Monday, August 11, 2008 - link
This article claims the PCIe slots are 1.x when they are in fact 2.0 as stated in the manual, website and other sources.Just wanted to make everyone aware of this. There are four total PCIe 2.0 that can run 2x PCIe 2.0 cards at x16/x16 or 4x PCIe 2.0 cards at x8/x8/x8/x8
To get around this, get an X2 version of the Radeon HD 3870 or 4870 and then crossfire with another one or drop down to a standard 3870/4870
MikeODanyurs - Wednesday, August 6, 2008 - link
Anyone see AMD OverDrive 2.1.2 available for download yet? It's Wednesday the 6th, official release day of 790GX+SB750.CZroe - Monday, July 28, 2008 - link
"it's unclear whether or not whatever AMD is doing here can even work on K8 if they tried."Nope. I've been waiting for a board/BIOS maker to expose this chipset setting since the Athlon XP Mobile Barton CPUs first made me aware of it. My Mobile Barton Athlon XP was basically a completely unlocked bin-sorted Athlon XP 3200+ that was stable at lower voltages expected to be run at much-lower voltages and clock speeds.
With it, I discovered that there was clearly a chipset setting not exposed when my Mobile Barton failed to reach 200/400FSB in an nForce2 Ultra400 board (the Shuttle board inside my SN45G XPC... the FN45-whatever IIRC) while the same CPU could easily do 450+FSB in an Asus A7N8X-E Deluxe and an Abit NF7-S. The solution? Drop a thin wire inside the socket to make this completely unlocked CPU *DEFAULT* to 400FSB and it runs perfectly fine and can even go higher (the L12 trick/mod).
With the default FSB being the only difference (all settings/frequencies, including the FSB, were the same), it was very clear that it was related to a calibration setting that was automatically applied by the chipset based on the default FSB (100MHZ/200FSB for this unlocked CPU). Previously, I could only get to 333FSB before Memtest 86+ would start giving errors. There were some reports of even the overclocking boards (mentioned earlier) getting higher with the L12 trick and later many had BIOS updates and board revisions that seemingly integrated the trick. Regardless, the setting was still not exposed and was likely not even something the board/BIOS makers could expose (though they could spoof the default FSB I'd assume). It looks like AMD, having full control of chipset and board-level options here, has finally let the cat out of the bag.
Although the FSB has become the HT bus, the behavior is the same. Changing the calibration setting allows for higher clocks while actually becoming unstable at lower clocks. Ever accidentally erased the OSCAL calibration value on a PIC microcontroller and had to find a working value through trial and error? I'm guessing that this is why it was automatic before.
initialised - Sunday, July 27, 2008 - link
Leads me to suspect that ACC is a means of adjusting the substrate potential to provide a bias to the bottom of the SOI stack to control the threshold voltage of the transistors.SirYes - Friday, July 25, 2008 - link
To spread the word: http://ubuntu-virginia.ubuntuforums.org/showthread...| To be honest I find it hard to believe that they have a campaign
| against Linux. There would be nothing to gain and would have
| a zero fiscal gain.
|
| I think it is a bug you have found
After looking through the disassembled BIOS for the last several hours, rebooting it, and tweaking it more, I'd say this is very intentional, I've found redundant checks to make sure it's really running on Windows, regardless what the OS tells it it is, and then of course fatal errors that will kernel panic FreeBSD or Linux, scattered all over the place, even in the table path for Windows 9x, NT, 2000, XP, and Vista, and had to correct them (Well, at least divert them off into a segment of RAM I hope to god I'm sure about)
No, this looks extremely calculated, it's like they knew someone would probably go tearing it apart eventually and so tried to scatter landmines out so as to where you'd probably hit one eventually.
So if it is a mistake, or incompetence, then it's the most meticulous, targeted, and dare I say, anal retentive incompetence I've seen.
Will14 - Friday, July 25, 2008 - link
I've never had much faith in Windows OC tools.However if this one actually works and AMD can up their speeds a little then I may switch back for my next system.
I must say my 6400-8400(cheated got an e3110 with 20% discount when first released and they were all $280 or OOS for $170). Upgrade path was seamless and I feel bad going from 1950Pro to 8800GT 512 but I follow my wallet not the company I root for.
A cheap system built off cheap Black Box edition(OC'd easily with their tool) and 4870x2 would be pretty sweet come this December if the new cores are kicking and the utils work(a lot of ifs). Not that I need a new system though, but if one did. I don't see nehalems being affordable anytime soon(unless new AMD core rocks(another if)), although my mobo would support. I like the $200 mark for processors $100 for HDD's $200 for gpu's plus generally only needing 1-4 new parts for a yearly $400ish upgrade which is cheaper and allows better performance than the $1-2k some people build.
Zisyncmon - Friday, July 25, 2008 - link
Does anyone know when they will release more info? Gary? Any estimates of when to expect another article? Or will we have to be in suspense all weekend.geok1ng - Thursday, July 24, 2008 - link
I am really hoping that AMD can make some competition on CPU market as they did on the IGP (man i am really looking forward to the next IGP offer from AMD, the 780G is the king, the next chip will be a market consolidating move for sure)and VGA markets but i am not joking when i ask:Will a 3.1Ghz ultraoverclocked quad core Phenom beat a $80 E2180@3,1Ghz in gaming and common day tasks?
As i remember the C2Ds are 15%-25% faster clock per clock, and the AMD CPUs consume MORE power for the same tasks , because they take LONGER to do the same task of a C2D.
jslusser - Thursday, July 24, 2008 - link
So does this ACC on the SB750 do anything for vanilla Phenom's? Will it unlock the multiplier on the non-black Phenoms or just make them more stable with the HT and memory over clocks?I'd like to see where the 9150e/9350e can get to with ACC and the power usage, since the voltage, etc doesn't change. So many questions...
HazaroudsSmoker - Friday, July 25, 2008 - link
First, you can't unlock the multiplier on the non Black Edition Phenoms. They are locked at the factory during manufacturing and can not be altered.Sounds like there will be an advantage still to having the SB750 with Vanilla Phenoms.
Can't wait for Benchmarks.