Voltage questions

[Tim]

I have an e8400, I'm running it at stock speeds atm.
I set voltage to 1.1225 or something like that in the bios.

CPU-z shows the voltage as 1.088
CPUID shows the voltage as 1.09
nVidia System Monitor shows the voltage as 1.119

Why are all of these numbers different, which one is the correct one?
Whats the stock voltage for the e8400 supposed to be in the first place?
Also, what's the best way to test to make sure my voltage that I set is stable?

 

[Tim]

... or not

 

[Tempered81]

i would trust cpu-z. Theres going to be vdroop. Your 1.12 in bios could equal 1.08 in cpuz and 1.065 when under heavy load.

 

[Mondoman]

The stock voltage for your specific CPU is encoded in the chip -- it's called the "VID" voltage. You can find it, for example, on the main data page of CoreTemp near the bottom. The range of VID's for a CPU model can be found by looking up the model's SSPEC at http://processorfinder.intel.com/
The reported voltage is lower than the set voltage because in the real world, adding a load normally lowers the voltage a bit. The spec sheet for the CPU shows how much the voltage is supposed to droop under different loads (shown as amps of current drawn by the CPU). Thus, you should see the reported voltage even lower under heavy load than at idle.

 

[Tim]

Unfortunately, CoreTemp doesn't play nice with my 64-bit vista ultimate.
The intel link you provided above shows the specs for my e8400 to be 0.85 to 1.3625.
So my goal since I plan on running this stock most of the time should be to get low as possible with my voltage I'd imagine. Is running orthos and Super-Pi enough to see if it's stable?

 

[imported_wired247]

I just used prime 95 (multi core) and small FFTs for 20+ hrs as was recommended on AT and it worked fine for me... no crashes since then, stable for days and days and days on end under folding@home

CPU-z is probably the closest to the "real" voltage as you can get, so don't pay that much attention to the mobo setting.

 

[Big Lar]

IMHO, The ONLY way to get the true voltage is to get a meter and take it off the board, for instance, Core Temp; supposed to be giving the correct Vid hard wired.. in the chip. Not true. I have on my board run 3 different versions of bios, and Core Temp shows 2 Different vids between them, ie; 10/17 bios is shown as 1.0375,12/24 and 02/13 show 1.125v. Draw your own conclusions from that.

Larry

 

[cpemma]

Originally posted by: thepladfad
I set voltage to 1.1225 or something like that in the bios.

CPU-z shows the voltage as 1.088
CPUID shows the voltage as 1.09
nVidia System Monitor shows the voltage as 1.119

CPUID (and Speedfan) round the voltage they measure to two decimal places, CPU-Z shows three, but all three are taking the same raw data and doing the same calculation, and they both show the figure at the CPU (after droop). There's also a thing called "spurious accuracy" very common with digital readouts, more digits =! more accurate.

Your nVidia SM is starting from a different data source so you're comparing apples and pears with that one. Just to add to the confusion, CoreTemp shows VID, which is the spec voltage for the CPU, not what it's being given - with everything on auto, the motherboard sets its output to VID for that CPU. *

I set 1.400 in BIOS and get 1.34 in Speedfan, 1.344 in CPUID, but that's overclocked 2G->2.9G so Vdroop is higher, plus some motherboards (eg, my Gigabyte) tend to have higher Vdroop than others. Vdroop is part of the Intel design scheme, so at the end of the day system stability is the only thing that matters.

( edit: * At least that's how it looks on my system, Big Lar has different evidence. But I'm taking the CoreTemp author's word. )

 

[Tim]

would just be nice if apples were apples and oranges were oranges

 

[lenjack]

Your 3 readings differ by only 0.031 volts. Not enought to worry about.

 

[Drsignguy]

Update on core temp. Go here, Text to get the hack for X64. When you do get it, make sure you disable your antivirus first, then start the "coretemp-startup" to load the driver then start core temp. Works very well after you do this. This will give you proper readings. Just an FYI.

 

[Tim]

Originally posted by: lenjack
Your 3 readings differ by only 0.031 volts. Not enought to worry about.

I never stated that I was worried, I simply wanted to know the reason for the offset.

 

[Tim]

Originally posted by: Drsignguy
Update on core temp. Go here, Text to get the hack for X64. When you do get it, make sure you disable your antivirus first, then start the "coretemp-startup" to load the driver then start core temp. Works very well after you do this. This will give you proper readings. Just an FYI.

Thanks, CoreTemp works now.

The stock voltage for your specific CPU is encoded in the chip -- it's called the "VID" voltage. You can find it, for example, on the main data page of CoreTemp near the bottom. The range of VID's for a CPU model can be found by looking up the model's SSPEC at http://processorfinder.intel.com/
The reported voltage is lower than the set voltage because in the real world, adding a load normally lowers the voltage a bit. The spec sheet for the CPU shows how much the voltage is supposed to droop under different loads (shown as amps of current drawn by the CPU). Thus, you should see the reported voltage even lower under heavy load than at idle.

Although coretemp works now with my vista 64bit, the "revision" feild and the "VID" feild are greyed out and no information is displayed. Any idea what that's all about?

I seem to be stable at 1.064v for now, I'll be testing lower tomorrow.
Accoriding to coretemp,At that voltage my idle is 26C, and load under Prime95 and SuperPi is around 36C. I'm assuming I can possible shave a degree or two with lower voltage? (assuming It will stay stable)

 

[Tim]

After a lot of testing, it seems my e8400 is happy running at these settings,
Bios, 1.0815v, Cpuz shows 1.056v idle, down to 1.040 during load (running prime 95) without errors.