Two kind-of-connected questions in one here (sorry, I'm lazy :-)).
1. Most CPU reviews/guides look at overclocking with respect to the stock voltage. However, do definitive values exist for a given CPU, or is this stock really specific to the mobo (and it's this that people report on in reviews)?
Having a look through all AMD's official tech sheets (for a Phenom II X3 720BE in my case), they only seem to give the voltage range: the "AMD Family 10h Desktop Processor Power and Thermal Data Sheet" gives 1.15 - 1.425V for P0 at 2800MHz.
I have understood that mobo manufacturers sometimes set the VCore high (for guaranteed stability, presumably) e.g. Asus: on my M3N78 Pro, it's reported as 1.4V in the BIOS, though reviews of this CPU suggest it's supposed to be 1.325V.
So do definitive values exist and where are they officially listed if so??
2. On this note, I've been using Phenom MSR Tweaker (PMT from now on...) since, on my board, CnQ turns off if I overclock the FSB (but, strangely, only on Win7 and not Vista). CPU-Z (and Asus PC Probe II) both match in giving a voltage of around 1.4V in the P0 state, yet I need to set the V in PMT at 1.325V to get CPU-Z to show this c. 1.4V voltage.
Any ideas why this is? My guess is that 1.325V is the official stock (still don't know how I find this out though!), which PMT sets via some given Windows BIOSy interface, and the Asus BIOS applies its own adjustment to this, as it does in the vanilla state. Just a guess but is this likely? I know that CPU-Z / HWMonitor can sometimes report wrong voltages depending on the monitoring chip, but the 1.4V matches what the BIOS HW Monitor says (from which, I also presume that it boots into the P0 state).
Sorry, ended up longer than I intended but any advice/info. appreciated.
Yes, the v core is a set value for a given CPU, I believe most of the phenom II's are 1.325 V.
Its possible for a motherboard (or software) to set the voltage higher, esp if you are using a board tweeking utility instead of simple bios overclocking. This is why many OC experts prefer to do manual BIOS overclocking, they want to have control over every aspect of their overclock.
I would set everything to manual in the bios and set your voltages and clocks to your own preferences.
OK, thanks buzznut. The 1.4V is what the BIOS hardware monitor reports at boot (so must boot into P0) and at the standard 200MHz FSB.
What I'm really trying to understand though is where this stuff's published. Presumably AMD provides some reference curve of voltage vs. frequency (or multiplier), which mobo manufacturers then take and may tweak according to their own testing and the specifics of their mobo hardware/BIOS.
So when reviews talk about "the 1.325V stock for a Phenom II X3 720", are they just going on what the mobo BIOS outputs at the default settings (as I said, it appears that Asus at least sets the voltages high, which I've seen other posts about, but maybe most others use reference values)? Or are they going on AMD's reference values? (But where do you get these?; couldn't find them anywhere in AMD's technical docs for download, only voltage ranges.)
Which shows an even wider range from .850-1.425V.
The wider range encompasses the lowered voltages for cool and quiet.
In this case I would say nominal voltage MAY be motherboard determinate, but it is likely that nominal or ideal voltage is ~1.3V at standard clock rates.
So why does it seem that ASUS is setting the voltages so high? Well, I haven't seen this personally except for a setting in the BIOS for "high performance" which may be ram related (or not, depending on your board). Setting it to high performance will cause the board to automatically raise voltages for stability. This is a setting that would be beneficial to a noob to overclocking, but for the rest of us it is best to keep all settings at auto or manual. Preferably manual if available.
Yes, it's strange; this is just with voltage on Auto and no high performance equivalent (I think my board calls these Ai Overclock settings....).
Reviews of other Asus boards with an X3 720 show a stock voltage of 1.325V, so maybe it's just poor BIOS on this particular board. Haven't got the absolutely latest version but all changes since mine are just for new CPUs.
I relooked at this because I was running fine with a manual 1.325V setting and a mild overclock (FSB 220). Worked fine for many months but recently had intermittent POST failures (just hangs and never beeps), which seem to have gone now I've restored Auto voltages (and hence 1.4V; I could obviously experiment manually with something in between but had zero stability problems with 1.325V *once in Windows* including various long stress test runs, heavy gaming, etc.)