PC Power Management Guide

[The_YongGrand]

Hey charge-and-go,

I happened to have the new Celeron 420 - the heatsink is really small, and it's just as cool as cucumber. The heat output - is absolutely minimal!! I touched the heatsink and it's just a little warm.

I don't have any measuring devices for wattage levels of CPU, but I'm pretty sure that it's really 35W...

[Dashken]

Today, we revisit the PC Power Management Guide with some inside information about the AMD Quad Core (Barcelona) Power Management and also some detailed explaination on EIST and C1E.

Have you ever wondered what all those C-state, P-state, S-state terms mean? Sure, you know they are related to power management in your PC, but what exactly do they do?

The PC Power Management Guide is here to answer all your power management questions. If you want to know what those terms mean, this is the guide for you.

Quote from the guide:-

Computer performance have increased at an amazing rate in recent years, and unfortunately so does power consumption. An ultimate gaming system equipped with a quad-core processor, two NVIDIA GeForce 8800 Ultra, 4 sticks of DDR2 memory and a few hard drives can easily consume 500W without doing anything! To reduce power wastage, a few industry standards have been developed to make our computers work more efficiently.

Link : PC Power Management Guide Rev. 2.0

[charge-n-go]

Originally Posted by The_YongGrand

Hey charge-and-go,

I happened to have the new Celeron 420 - the heatsink is really small, and it's just as cool as cucumber. The heat output - is absolutely minimal!! I touched the heatsink and it's just a little warm.

I don't have any measuring devices for wattage levels of CPU, but I'm pretty sure that it's really 35W...

It is actually around 25 - 30W when full load and averaging about 15-20W
I am still waiting for my single core to arrive. Time unknown yet

[The_YongGrand]

Originally Posted by charge-n-go

It is actually around 25 - 30W when full load and averaging about 15-20W
I am still waiting for my single core to arrive. Time unknown yet

You are buying a low-wattage single core too? The Celeron 420 is the best one, for those budget mini-ITX replacements.

I happen to purchase another new Asus P5PE-VM and that will be paired with my Celeron 420.

And I don't have to hunt around for 35W Semprons. I now have a new replacement.

The another Intel board with onboard processor (don't know what model already, something ends with GLY) only drinks up 29W for the processor.

[charge-n-go]

Originally Posted by The_YongGrand

You are buying a low-wattage single core too? The Celeron 420 is the best one, for those budget mini-ITX replacements.

I happen to purchase another new Asus P5PE-VM and that will be paired with my Celeron 420.

And I don't have to hunt around for 35W Semprons. I now have a new replacement.

The another Intel board with onboard processor (don't know what model already, something ends with GLY) only drinks up 29W for the processor.

Yea, Sempron is really cheap, but the performance isn't good. From Tomshardware CPU Power chart, Sempron is godlike in terms of power consumption. Although AMD published 35W, but it will be way lesser, bcoz 35W is its super max load power which we cannot reach in real life.

Yeap, I will be getting a 2.8GHz Celeron (Core 2 Solo?) 1MB version in a few weeks time. Most probably will pair up with Biostar T-force and a low power graphic card. Going to give this to my daddy to replace his old K7 Sempron

[Chai]

Originally Posted by charge-n-go

Thanks dude.

Alrite, here is your answer

EIST -
manages processor P-state in the C0 state only.

C1E -
manages processor P-state in C1 state, using the same logic circuit in EIST.

Cool and Quiet -
manages all the processor power management states, including P-states and C-states. So far it has up to C1E for desktop variant. I don't know how far the Turion's CnQ goes, but i guess it would be at least C2 and above.


I am not sure about Vista, you can try the Windows XP method - change the power scheme to max battery saving.

Are you sure about EIST?

From my experience, EIST manages the same way as C1E. Both will drop voltage and multiplier at 0% load. The only difference that I see is this:
1. EIST requires OS/driver support unlike C1E.
2. EIST drops the voltage of my processor to stock voltage, while C1E drops even more, down to 1.1V, causing stability issue, on my overclocked C2D that is.

[charge-n-go]

Originally Posted by Chai

Are you sure about EIST?

From my experience, EIST manages the same way as C1E. Both will drop voltage and multiplier at 0% load. The only difference that I see is this:
1. EIST requires OS/driver support unlike C1E.
2. EIST drops the voltage of my processor to stock voltage, while C1E drops even more, down to 1.1V, causing stability issue, on my overclocked C2D that is.

Yes I am absolutely sure about EIST.

1. EIST (a.k.a. P-state) requires OS support, I mentioned in the guide.
2. C1E uses EIST circuit to lower down the Vcore to 6x multiplier / 1.1V, because Intel defines C1E must use 6x multi with 1.1V (for certain stepping it is even lower). EIST is OS (Windows) controlled, I have no knowledge on how WinXP implements P-state.

[Chai]

I think you need to read what I've just said.

This is from my personal experience, I can show screenshot as proof. C1E was disabled in the BIOS, only EIST. No power saving was active in Windows until I set the power scheme to Laptop. And both voltage and multiplier dropped. And EIST was only active at C1 state.

[charge-n-go]

Originally Posted by Chai

I think you need to read what I've just said.

This is from my personal experience, I can show screenshot as proof. C1E was disabled in the BIOS, only EIST. No power saving was active in Windows until I set the power scheme to Laptop. And both voltage and multiplier dropped. And EIST was only active at C1 state.

If you are really interested to know how EIST work, I can start from the basic. First of all, EIST is controlled by writing some value to IA32_PERF_CTL register (MSR 0x199) as stated in Intel Manual Volume 3B Appendix B-55. Those values consist of clock ratio and VID that the CPU must run at. So what Windows XP does is to write this register when laptop power scheme is enabled. Microsoft just doesn't like the idea of having desktop PC to use EIST feature by default !!

C1E is a HALT state with lowest P-state enabled. This is a hardware mechanism where the CPU will automatically write the IA32_PERF_CTL register with the lowest possible clock ratio and VID (6x and 1.1V) to force the CPU to the lowest possible clock speed. There is a dedicated piece of hardware (circuit) to read the value in IA32_PERF_CTL register, translate them into the correct voltage and PLL signals and transition the CPU to the specific state. That is why I said C1E and EIST are using the same circuit, and the circuit name is commonly referred as EIST (P-state) circuit because its main function is to control the clock ratio and VID.

It's up to you to believe or not. I have real life of experience in the CPU power management hardware, I m very sure I don't provide misleading info here.

[Chai]

Originally Posted by charge-n-go

If you are really interested to know how EIST work, I can start from the basic. First of all, EIST is controlled by writing some value to IA32_PERF_CTL register (MSR 0x199) as stated in Intel Manual Volume 3B Appendix B-55. Those values consist of clock ratio and VID that the CPU must run at. So what Windows XP does is to write this register when laptop power scheme is enabled. Microsoft just doesn't like the idea of having desktop PC to use EIST feature by default !!

C1E is a HALT state with lowest P-state enabled. This is a hardware mechanism where the CPU will automatically write the IA32_PERF_CTL register with the lowest possible clock ratio and VID (6x and 1.1V) to force the CPU to the lowest possible clock speed. There is a dedicated piece of hardware (circuit) to read the value in IA32_PERF_CTL register, translate them into the correct voltage and PLL signals and transition the CPU to the specific state. That is why I said C1E and EIST are using the same circuit, and the circuit name is commonly referred as EIST (P-state) circuit because its main function is to control the clock ratio and VID.

It's up to you to believe or not. I have real life of experience in the CPU power management hardware, I m very sure I don't provide misleading info here.

Actually, I agree with most of your info except this.

"EIST -
manages processor P-state in the C0 state only."

Are you sure it's C0 state, not C1 state? Because everything you said is right, except that, from my experience anyway. I mean, I see no purpose in having EIST when it's in C0 state. While would you want to throttle the CPU when there's CPU usage?